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This information is produced and provided by the National Cancer Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via the Internet web site at http://cancer.gov or call 1-800-4-CANCER.
Cancer patients often have comorbid medical problems in addition to their underlying malignant disorders. In fact, patients older than 65 years bear a disproportionate burden of cancer as well as increased prevalence of medical problems such as chronic obstructive pulmonary disease, heart disease, diabetes, and hypertension. Whether patients are seen in primary care or cancer care settings, unexplained symptoms often frustrate physicians and patients. Because many advanced cancers spread to the thorax, symptoms such as dyspnea, cough, chest pain, or palpitations often present a challenge in sorting out the likely cause of the problem and developing appropriate interventions. Evidence-based recommendations have been published describing various approaches to the problems of cancer-related fatigue, anorexia, depression, and dyspnea. Cancer patients are often also at higher risk for pulmonary infections.
Clinicians caring for cancer patients should be familiar with the assessment and treatment of common conditions that manifest as chest symptoms. In addition, these clinicians need to be familiar with some cancer-specific aspects of chest symptoms and syndromes. Dyspnea is a common symptom of certain cancers such as lung cancer and is also common in patients with numerous advanced cancers. It is often multifactorial. Optimal treatment requires an understanding of contributing etiologies and pathophysiologies to direct therapeutic interventions as clinically appropriate. Important cardiopulmonary syndromes include malignant pleural effusion, malignant pericardial effusion, superior vena cava syndrome, and lymphangitic carcinomatosis.
In this summary, unless otherwise stated, evidence and practice issues as they relate to adults are discussed. The evidence and application to practice related to children may differ significantly from information related to adults. When specific information about the care of children is available, it is summarized under its own heading.
Dyspnea is defined as an uncomfortable awareness of breathing. It is a subjective experience involving many factors that modulate the quality and intensity of its perception. Patients with comparable degrees of functional lung impairment and disease burden may describe varying intensities of dyspnea. Patients use a host of different words and phrases to describe the sensation of breathlessness. Terms such as tightness and suffocating are sometimes used.
Reports on the frequency of dyspnea also vary, depending on the setting and the extent of disease. In one study, 49% of a general cancer population reported breathlessness, and 20% rated their breathlessness as moderate to severe. Patients with advanced cancer experience this symptom more frequently and more intensely than do patients with limited disease. One study found that 75 of 135 patients with advanced cancer reporting to an outpatient palliative care clinic were experiencing moderate-to-severe dyspnea. Breathlessness was a complaint at presentation in 60% of 289 patients with lung cancer. Results of a large study showed that 70% of patients suffered from dyspnea in the last 6 weeks of life. About one-third of patients who could report the intensity of their dyspnea rated it as moderate to severe. Another study revealed that half of patients with advanced cancer scored their dyspnea as moderate to severe.
Pathophysiology and Etiology
The pathophysiological mechanisms of breathlessness are numerous and complex. Peripheral and central mechanisms as well as mechanical and chemical pathways are involved with a variety of sensory afferent sources.[9,10,11]
The qualities of dyspnea can be appreciated as work/effort, tightness, and air hunger. The experience of excess work and effort is caused by sensory-perceptual mechanisms similar to those involved in muscles exercising. Tightness is caused by stimulation of airway receptors with bronchoconstriction. Intensity of air hunger and unsatisfied inspiration is caused by imbalances of respiratory drive, outgoing signals from the brain, and feedback from afferents in the respiratory system.
The direct causes of dyspnea in patients with advanced cancer are numerous; categorizing them can assist in the etiologic work-up. One approach is to divide direct causes into the following four groups:
One study found that in patients experiencing dyspnea from advanced cancer, a median of five different abnormalities could have contributed to their shortness of breath. Spirometry was abnormal in 93% of 100 patients examined, with 5% having obstructive patterns, 41% restrictive patterns, and 47% mixed patterns; 49% of patients had lung cancer, 91% had abnormal chest radiographs, and 65% had parenchymal or pleural involvement. These results indicate that a subset of patients will experience shortness of breath without any apparent lung involvement. The potentially correctable causes of dyspnea included hypoxia (40%), anemia (20%), and bronchospasm (52%). No significant association between the type of respiratory impairment and the degree of dyspnea was found. Most of these patients were current or former smokers. Most patients also had a significant lowering of their maximum inspiratory pressures, suggesting severe respiratory muscle dysfunction. This finding was duplicated in another study. Of patients admitted to hospice care, 34% had histories of cardiac disease and 24% had histories of respiratory disease. Only 39% of terminally ill patients who reported dyspnea had lung or pleural involvement. The etiology of dyspnea could not be clearly identified in approximately one-quarter of patients. Another study found that 49% of lung cancer patients presented with airflow obstruction.[7,13]
Respiratory muscle dysfunction is an underrecognized factor contributing to dyspnea. Causes of respiratory muscle dysfunction include neuromuscular disease, malnutrition, and deficiencies of potassium, magnesium, and inorganic phosphate. Poor oxygenation, muscle fatigue, abnormal cortisol and catecholamine levels, and circulating cytokines are also implicated.
Although it is commonly believed that anxiety is associated with breathlessness, researchers found that anxiety and shortness of breath do not invariably go together. One study demonstrated that the involvement of the lungs by cancer, anxiety, and poor maximal inspiratory pressures were correlates of the intensity of dyspnea in patients with advanced cancer.
The multidimensional nature of dyspnea must be noted in the complicated assessment of this symptom. Patient-reported outcome is the gold standard for assessment of dyspnea. There is no consensus on what constitutes the best instrument for assessing dyspnea. Visual analog and numerical rating scales appear to be useful and are commonly utilized.[8,15,16,17] The Borg Scale is occasionally utilized. The Cancer Dyspnea Scale is a multidimensional instrument, initially developed in Japan for patients with lung cancer and later translated into Swedish. This scale has been shown to be valid and reliable in patients with advanced lung cancer. The subscales measure sense of effort (physical dimension), sense of anxiety (psychological dimension), and sense of discomfort. These tools are limited, however, because they are unidimensional and do not account for the relative contribution of different factors to a patient's perception of breathlessness. Assessment should include the impact of dyspnea on the patient's functional status and appreciation of the dynamic component of dyspnea—namely, exertional dyspnea.
Objective signs such as tachypnea or the use of accessory breathing muscles frequently do not match a patient's perception of dyspnea and the degree of functional impairment it causes. Numerous factors, including psychosocial issues, may affect a patient's experience of dyspnea. Pulmonary function tests, with few exceptions, play a limited role in the assessment of this syndrome. Lack of a clear understanding of the pathophysiological mechanisms underlying dyspnea hampers the clinician's overall ability to effectively manage it.[8,15]
A comprehensive history and examination are essential to an accurate assessment of dyspnea.[8,15] The temporal onset, qualities of the symptom, associated symptoms, precipitating and relieving events or activities, and responses to medications should be reviewed. Sudden onset may herald a pulmonary embolism or infection, whereas gradual onset may suggest the development of a pleural effusion. A history of obstructive airways or cardiac disease can shed some light on possible underlying causes. Investigations such as measuring oxygen saturation can be useful in determining whether a patient is hypoxic. In the setting of advanced, incurable cancer, arterial blood gasses play a limited role.
Diagnostic tests that may help to determine the etiology of dyspnea include chest imaging by radiography, computer-assisted tomography, complete blood counts, oxygen saturation at rest and with exercise and, to a much lesser extent, pulmonary function tests. Maximal inspiratory pressure (MIP) measurements may be helpful, particularly if no apparent cause can be found. MIP is a reliable functional test of the strength of the diaphragm and other respiratory muscles. Functional assessments such as the 6-minute walk test and exercise ergometry may also provide valuable information about the severity and impact of dyspnea.[19,20]
Management of Dyspnea
Management of underlying causes
As with all symptoms, it is essential to identify and treat the underlying cause(s) of dyspnea if possible and when appropriate. Examples of specific underlying causes (some of them potentially reversible) and their treatments include the following:
Symptomatic management of dyspnea is based primarily on oxygen therapy, opioids for palliation of dyspnea, and treatment of underlying causes (e.g., superimposed infection) when appropriate.
Opioids represent an extremely effective treatment for dyspnea in cancer patients. Fear of side effects should not prevent the appropriate use of opioids in this setting. Most authorities believe that, if used appropriately, opioids do not hasten death in dyspneic cancer patients; rather, they reduce physical and psychological distress and exhaustion, and early use improves quality of life.[15,22] Clinically significant hypoventilation following opioid therapy depends largely on the history of previous exposure to opioids and the rate of increase of the opioid dose. As with opioid use in pain management, the principles of starting at a regular low dose in opioid-naïve patients followed by appropriate dose titration applies. Opioid therapy for dyspnea is administered similarly to, and often concurrent with, opioid therapy for pain control. Most of the available evidence supports the role of opioids in relieving dyspnea in malignant and nonmalignant conditions.[23,24][Level of evidence: I];[25,26,27][Level of evidence: II]
Anecdotal and experimental evidence suggest a role for nebulized opioid administration in the treatment of dyspnea.[28,29,30] Opioid receptors are present on sensory nerve endings in the airways; however, nebulization is an inefficient way of administering drugs. Pharmacokinetic studies suggest that the systemic bioavailability of nebulized morphine is extremely poor and erratic, varying from 4% to 8%. Some patients may experience claustrophobia. Available evidence does not support the clinical use of nebulized opioids. More clinical trials are needed to better determine the role of this mode of treatment.
Patients who are hypoxic on room air are likely to benefit from oxygen therapy, probably through a decrease in the chemoreceptor input to the respiratory center and the brain cortex. In two controlled trials, cancer patients with dyspnea who were randomly assigned in a crossover design showed significant improvement in their dyspnea.[32,33][Level of evidence: I] The role of supplemental oxygen has also been examined in patients without hypoxemia in a large randomized controlled trial. Supplemental oxygen given at 2 L/min did not significantly improve dyspnea, compared with supplemental air. Therefore, supplemental oxygen is recommended for cancer patients with hypoxemia but not for those who are nonhypoxemic.
Other investigators have examined the effect of other oxygen delivery modalities on dyspnea in cancer patients, such as high-flow oxygen and noninvasive ventilation with bilevel positive airway pressure (BiPAP). High-flow oxygen devices deliver up to 40 L of humidified and heated oxygen per minute, and may reduce the intensity of dyspnea in patients who do not respond to low-flow oxygen. BiPAP has also been shown in several randomized controlled trials to alleviate dyspnea among hospitalized cancer patients,[35,36] particularly in patients with hypoventilation. These interventions may be reasonable options for patients with hypoxemia and refractory dyspnea despite the use of low-flow supplemental oxygen.
Other options suggested for symptomatic treatment include methylxanthines, sedatives, tranquilizers, nebulized local anesthetics, and antiprostaglandins. The role of methylxanthines in cancer-related dyspnea has not been clarified. Chlorpromazine and promethazine have been shown to decrease dyspnea without affecting ventilation in noncancer patients, but their role in cancer-related dyspnea is unclear. Four out of five randomized controlled trials failed to demonstrate any benefit for using benzodiazepines in cancer patients.;[Level of evidence: I] One randomized single-blind study suggests that the combination of two scheduled medications (subcutaneous morphine and subcutaneous midazolam) and one as needed (subcutaneous morphine) for episodes of breakthrough dyspnea is more effective than the other evaluated combinations for controlling breakthrough dyspnea and requires further study.[Level of evidence: I] The role of benzodiazepines appears to be limited to treatment of dyspnea that is considered a somatic manifestation of a panic disorder or use when a patient has concurrent severe anxiety. No evidence supports the use of nebulized local anesthetics for the treatment of breathlessness.
General support measures
In addition to adequate pharmacological therapies, a number of nonpharmacological measures are suggested. These include pursed-lip breathing, diaphragmatic breathing and muscle training, cold air directed across the cheek, meditation, relaxation training, biofeedback techniques, and psychotherapy. The effectiveness of these measures in relieving breathlessness appears to be variable.
Current Clinical Trials
Check NCI's list of cancer clinical trials for U.S. supportive and palliative care trials about dyspnea that are now accepting participants. The list of trials can be further narrowed by location, drug, intervention, and other criteria.
General information about clinical trials is also available from the NCI Web site.
In some patients, chronic coughing may be the source of major suffering. Chronic cough can cause pain, interfere with sleep, aggravate dyspnea, and worsen fatigue. The causes of cough can be classified much like the causes of dyspnea.
One approach to chronic cough in palliative care patients is to consider the differential diagnoses summarized below:
The optimal therapy for chronic cough is treatment of the underlying disorder, such as:
Cough-suppressing agents such as opioids are commonly utilized. Anecdotal evidence suggests a role for inhaled local anesthetics, which should be utilized judiciously and sparingly; they are unpleasant to the taste and obtund the gag reflex, and anaphylactic reactions to preservatives in these solutions have been documented. Opioid and nonopioid antitussives, such as dextromethorphan, may act synergistically, but further studies are required to confirm this hypothesis. Gabapentin was found to be efficacious compared with placebo for chronic refractory cough, although this study did not specifically include cancer patients.
In cases of increased sputum production, expectorants and mucolytics have been employed, but the effects have not been well evaluated. Inhaled sodium cromoglycate has shown promise as a safe method of controlling chronic coughing related to lung cancer.
Malignant pleural effusions are a common complication of malignancy, and malignancy is a common cause of pleural effusions in general. Malignancy accounts for roughly 40% of symptomatic pleural effusions, with congestive heart failure and infection being the other leading causes. Lung cancer, breast cancer, lymphoma, and leukemia account for approximately 75% of all malignancy-associated effusions. Significant use of health care resources is attributable to malignant effusions, with approximately 100,000 cases per year being diagnosed in the United States and 43 cases being detected per 100,000 hospital admissions.
The normal pleural fluid space is occupied with approximately 10 cc of fluid with 2 g/dL protein. A pleural effusion is an accumulation of an abnormal amount of fluid between the visceral and parietal pleura of the chest. Normally, pleural fluid is absorbed by pulmonary venous capillaries (80%–90%), with some of it also absorbed by pleural lymphatics. Malignant effusions are usually exudative rather than transudative. Exudative effusions exhibit any one of the following characteristics:
These exudative malignant effusions are generally caused by pleural metastases, disruption of pulmonary capillary endothelium, or malignant obstruction of pleural lymphatics. Paramalignant effusions may result from chemotherapy, radiation therapy, atelectasis, or lymph node involvement.
Common symptoms associated with malignant pleural effusions include dyspnea, cough, and chest discomfort. About 20% of patients may experience weight loss and malaise. A chest x-ray is most commonly used for radiographic assessment. About 175 cc of pleural fluid will cause a blunted costophrenic angle discernible on chest radiography. A chest computerized tomography scan is more sensitive than a simple chest x-ray and is often used for assessment of loculated effusions because, in some instances, up to 500 cc of loculated fluid can be obscured behind the dome of the diaphragm.
Not all pleural effusions detected in cancer patients will turn out to be malignant effusions. Cancer patients are prone to developing conditions such as congestive heart failure, pneumonia, pulmonary embolism, malnutrition, and associated low serum albumin, each of which may cause a symptomatic effusion for which the clinical management would substantially differ from the management of a malignant effusion. For this reason, cytologic assessment is important. Pleural fluid cytology requires a minimum sample of 250 cc. The morphology of cells obtained from the pleural space can be difficult to assess because of mesothelial and macrophage abnormalities. The diagnostic sensitivity of pleural fluid cytology is approximately 65%, with a specificity of 97%. Flow cytometry can be applied to these specimens and is often useful, especially for assessment of lymphomas. Thoracoscopy and pleural biopsy are rarely needed for definitive diagnosis, but these techniques may be useful when routine pleural fluid collection and assessment are difficult because of loculation of the effusion. Thoracoscopy-guided biopsy is generally performed under local anesthesia and has a yield of more than 80%, with a lower risk of complications than thoracotomy.
Management of Malignant Pleural Effusions
To treat or not to treat
Pleural effusions are generally markers of advanced, unresectable disease or disease progression. The median survival for patients with malignant pleural effusions is around 3 to 4 months.[4,5] Because a paramalignant effusion resulting from pneumonia or atelectasis may be present, the cytology should be confirmed before major treatment decisions are made. Once the cytology has been confirmed, the management strategy depends on the underlying primary malignancy and the number and type of previous therapies. For example, patients with newly diagnosed small cell carcinoma or malignant lymphoma are very likely to respond to systemic chemotherapy; however, patients who have already failed several lines of chemotherapy for gastric or ovarian cancer are unlikely to obtain significant palliation with systemic therapy.
About three-quarters of patients exhibit symptoms such as cough, dyspnea, and chest discomfort. Such patients may benefit from efforts to reduce the fluid burden, depending on their performance status, expected survival, and preference for risks versus benefits. The literature on the efficacy of treatment for pleural effusions is difficult to interpret because of the paucity of randomized trials, and the wide variability in the response criteria and the timing and duration of follow-up in uncontrolled trials.[6,7] Generally, the goal of therapy is palliation of symptoms. Measures of success may include complete drainage of the effusion, lung re-expansion, lack of fluid reaccumulation (i.e., duration of response), and subjective report of symptom relief. The choice of treatment depends on patient prognosis, functional status, and goals of care.
Thoracentesis involves percutaneous insertion of a needle for drainage of the effusion. Thoracentesis is not expected to permanently resolve the problem but rather to alleviate symptoms that are acute and severe. The use of thoracentesis is also appropriate as a therapeutic trial to determine whether fluid drainage is beneficial when the relationship between symptoms and effusion is unclear.
Most effusions will reaccumulate a few days after thoracentesis. The reaccumulation rate is approximately 98% by day 30. Repeated thoracenteses carry the potential risks of bleeding, infection, and pneumothorax. Other potential complications of thoracentesis include noncardiogenic pulmonary edema from rapid lung re-expansion (usually with the rapid removal of >1,500 cc) and pleural shock caused by an excessive vagal response to penetration of the parietal pleura. Any of these complications may be lethal, especially for the cancer patient with poor cardiopulmonary reserve.
Chronic long-term indwelling tunneled pleural catheters
Indwelling pleural catheters (IPCs) represent an alternative to pleurodesis for patients with malignant pleural effusion whose dyspnea has responded to thoracentesis. IPCs are relatively contraindicated in patients with a short life expectancy, pleural infections, multiloculated collections, and chylothorax. The insertion of chronic long-term indwelling tunneled pleural catheters is useful against recurrent and symptomatic malignant pleural effusions, including for patients with trapped lung. These tunneled pleural catheters allow up to 96% of patients to achieve symptom improvement, with spontaneous pleurodesis occurring in up to 44% of patients. Published results indicate significantly shorter hospital stays (1 day) for patients with IPCs versus the doxycycline pleurodesis group (6 days). In the IPC group, spontaneous pleurodesis was achieved in 42 of 91 patients. Both the IPC group and doxycycline pleurodesis group reported modest improvement in quality of life and dyspnea. A randomized controlled trial comparing IPC and talc pleurodesis showed similar reduction of dyspnea (24 mm of 100 mm) and similar quality of life. IPC use was associated with a shorter initial hospitalization and lower rates of re-treatment, with a spontaneous pleurodesis rate of 51%. However, there were also higher rates of adverse effects, such as infections and catheter blockage. The choice between IPC and pleurodesis should be based on patient preference and local resource availability.
Use of pleural sclerosing agents after chest tube drainage
Chemical sclerosants may be administered through a chest tube to create inflammation and subsequent fusion of the parietal and visceral pleura so that fluid cannot reaccumulate in this potential space. This kind of fusion is called pleurodesis. Numerous chemical agents can cause the irritation necessary to produce pleurodesis. The ideal agent would produce effective pleurodesis with minimal cost and minimal side effects. Agents that have been studied include chemotherapeutic agents (bleomycin, cisplatin, etoposide, doxorubicin, mitomycin-C, fluorouracil), antibiotics (doxycycline, minocycline, tetracycline), infectious agents (Corynebacterium parvum), biological agents (interferon beta, interleukin-2), bovine dermal collagen,[Level of evidence: II] and other agents (talc, methylprednisolone). Several uncontrolled trials and case series report the efficacy of pleurodesis,;[14,15][Level of evidence: II];[16,17] as do numerous randomized trials.[18,19,20,21,22,23,24][Level of evidence: I] A meta-analysis of pleurodesis studies that were reported between 1966 and 1992 indicates that about two-thirds of patients respond to pleurodesis and that tetracyclines (or tetracycline replacement agents, such as doxycycline and minocycline), bleomycin, and talc appear to be the most effective agents. A prospective, randomized study of video-assisted thoracoscopic pleurodesis with talc versus doxycycline in 33 patients with malignant pleural effusion suggests that talc provides superior short-term and long-term results.[Level of evidence: I] Talc appears to be the least expensive agent, at least when given as a slurry rather than by video-assisted thoracoscopic talc insufflation.[Level of evidence: I] Bleomycin, however, is the only agent approved by the U.S. Food and Drug Administration for the prevention of recurrent pleural effusions. An observational cohort study investigated the use of intrapleural urokinase in 48 patients with loculated pleural effusions or trapped lungs. Lung reexpansion and resolution of dyspnea occurred in approximately 60% of patients, suggesting that intrapleural urokinase may be useful in treating loculated pleural effusions or trapped lungs in medically inoperable cancer patients. Most responders successfully maintained pleurodesis when urokinase was followed by minocycline pleurodesis.[Level of evidence: II]
For rare patients, standard management of the malignant effusion is unsuccessful and aggressive treatment remains appropriate. Pleuroperitoneal shunting can be considered for these patients. This procedure involves implantation of a shunt with one-way valves that allow the transfer of fluid from the pleural space to the peritoneal space, in which the fluid creates less hazard and is more easily removed. Another option is surgical pleurectomy, but this procedure requires general anesthesia. The risks of significant acute and chronic pain as well as other morbidity approaches 20% to 25%, and the risk of 1-month mortality is 5% to 10%.
Check NCI's list of cancer clinical trials for U.S. supportive and palliative care trials about malignant pleural effusion that are now accepting participants. The list of trials can be further narrowed by location, drug, intervention, and other criteria.
Malignant pericardial effusions occur in up to 21% of cancer patients [1,2,3] and are frequently not suspected until clinical signs or symptoms of pericardial tamponade develop. Two-thirds of patients have subclinical pericardial effusions with no overt cardiovascular signs or symptoms.[5,6] One-half of cases of pericardial effusion initially present with symptoms of cardiac tamponade. In 50% of cases, pericardial effusion is the first sign of malignant disease. Symptoms of pericardial effusion are often attributed to the underlying cancer. Dyspnea, fatigue, or asthenia may be the initial symptoms. Symptomatic pericardial effusions are often a preterminal event; however, significant symptom palliation can be achieved by prompt diagnosis and management.
Of patients with malignant pericardial effusions, 50% will have concomitant pleural effusions, and one-third will have pulmonary parenchymal disease.
One-third of patients with pericardial metastases will eventually die from pericardial tamponade. Pericardial involvement contributed to the cause of death in 85% of patients in a series reported in 1962 but in only 46% of patients in a recent study. Improvements in diagnostic and therapeutic options account for the decrease in mortality over the past 40 years.
Incidence and Prevalence
Malignant pericardial effusion occurs in up to 21% of autopsy cases in patients with common malignancies.[4,7] Of patients with lung cancer, 33% have pericardial metastases at autopsy, and one-third of cases of pericardial metastases are caused by lung cancer. Breast cancer causes 25% of pericardial effusions, and about 25% of patients with breast cancer have pericardial effusion. Hematological malignancies (leukemia, Hodgkin disease, non-Hodgkin lymphoma) cause 15% of cases of malignant pericardial effusions.
A retrospective review of 23,592 effusions over a 24-year period revealed 65 malignant effusions (17%) out of 375 pericardial effusions. Lung cancer was the most common cancer found among the malignant pericardial effusions in males, and breast cancer was the most common in females. In 43% of cases, pericardial effusion was the first detected sign of cancer. Of patients diagnosed with malignant pericardial effusions, 86% died within 1 year of diagnosis, with nearly one-third dying within the first month.
In a study of 31 patients with both cancer and pericardial effusions, malignant pericardial effusion accounted for 58% of the effusions, 32% were caused by benign idiopathic pericarditis, and radiation pericarditis caused 10% of cases.[11,12]
Malignant involvement of the pericardium is the most common reason for development of pericardial effusions, which result from blockage of venous and lymphatic circulation of pericardial fluid. Such blockage may be caused by primary malignancy of the pericardium, as with pericardial mesothelioma, or by tumors arising in the myocardium, including angiosarcoma, rhabdomyosarcoma, and malignant fibrous histiocytosis. Malignancies can also involve the pericardium through direct extension from carcinomas of the lung or esophagus, thymoma, or lymphoma. Lymphatic or hematogenous metastasis to the pericardium occurs most commonly with carcinomas of the breast and lung, leukemia, lymphoma, and melanoma. Primary tumors of the pleura or pericardium have recently been termed primary intrathoracic malignant effusions.
Nonmalignant causes of pericardial effusion include pericarditis, myocardial infarction, uremia, hypothyroidism, systemic lupus erythematosus, trauma, postsurgical pericardiotomy syndrome, and intrapericardial hematomas.[14,15,16] AIDS may also cause pericardial effusion with pericarditis. Radiation therapy or chemotherapy drugs can cause pericarditis without metastatic involvement of the pericardium. Radiation pericarditis is usually associated with radiation doses to the cardiac window exceeding 30 Gy  and occurs most frequently in patients who have received mediastinal radiation for Hodgkin disease or breast cancer. Doxorubicin and cyclophosphamide have been associated with the development of acute pericarditis with effusions.[11,12] Other drugs that may cause acute pericarditis include procainamide, hydralazine, isoniazid, methysergide, phenytoin, and anticoagulants.
Pericardial tamponade results from progressive fluid accumulation in the pericardial sac, causing elevated intrapericardial pressure, diminished stroke volume, decreased cardiac output, progressive decrease in cardiac diastolic filling, and hemodynamic compromise resulting in death if not treated. Hemodynamic compromise occurs when the normal amount of pericardial fluid (approximately 15–50 cc) increases to 200 cc to 1,800 cc.[15,18] When fluid accumulates rapidly, as little as 250 cc of fluid can result in tamponade.[11,19]
Dyspnea occurs in 93% of patients with pericardial effusions. Cough, chest pain, and orthopnea (discomfort with breathing while lying flat) are common symptoms. Other symptoms of pericardial effusion include upper abdominal distention or pressure caused by downward hepatic distention, hiccups resulting from pressure on the diaphragm, or pleuritic pain caused by stretching of the pericardium (especially when lying flat). Signs of effusion include Kussmaul's sign (increased distention of jugular veins with inspiration), Freidreich's sign (rapid diastolic descent of the venous pulse), and pulsus paradoxus (decrease of more than 10 mm Hg in the diastolic pressure on inspiration). Pericardial friction rubs and fever are more commonly associated with nonmalignant causes of pericardial effusions than malignant etiologies.
Signs of pericardial tamponade include tachycardia, pulsus paradoxus, elevated jugular venous pressure, and hypotension; however, some patients may develop tamponade without this clinical pattern.
A chest x-ray may show widening of the cardiac silhouette  if the amount of pericardial fluid collection exceeds 250 cc; however, a chest x-ray cannot determine the degree of cardiac dysfunction or tamponade. Loculated pericardial effusions may not be apparent on standard posterior/anterior or lateral chest radiographic views.
Transthoracic echocardiography using apical, subxiphoid, and parasternal views can evaluate the presence, quantity, and quality of suspected pericardial effusions as well as associated pericardial masses and inflammation. Moderate effusions on echocardiography show an echo-free space of 10 mm to 20 mm during diastole in M-mode or 2-dimensional echocardiography, whereas severe effusions have an echo-free space exceeding 20 mm.[21,22] Echocardiography can also determine right and left ventricular function and the possibility of right ventricular or atrial diastolic collapse. Left ventricular collapse caused by large pleural effusion without clinically significant pericardial effusions has been reported;[4,16,23,24] however, transesophageal echocardiography may be useful for loculated effusions resulting from adhesions adjacent to the atria, where the thinness of the atrial wall may not be well visualized on transthoracic echocardiography.[4,16]
Echocardiography in pericardial effusion with tamponade shows right atrial or right ventricular compression, or left atrial compression, decreased left ventricular dimension, and absence of collapse of the inferior vena cava on deep inspiration.[6,25] Echocardiography findings predictive of pericardial tamponade have been reported. Right atrial collapse has a sensitivity of 55% to 60% and a specificity of 50% to 68%. Right ventricular diastolic collapse has a lower sensitivity of 38% to 48% but a higher specificity ranging from 84% to 100%. Because neither finding provides 100% sensitivity and specificity, patients who are clinically symptomatic should have a diagnostic pericardiocentesis, even in the absence of definitive findings on echocardiography.[4,27] One study found right atrial collapse present in only 42% of patients and right ventricular collapse in 62%. Nonetheless, 80% of patients with malignant pericardial effusions had symptomatic relief following pericardiocentesis.
The most definitive test for the diagnosis of cardiac tamponade is equalization of diastolic pressures between all cardiac chambers on right-heart cardiac catheterization. This invasive technique, however, is not necessary to diagnose tamponade.
Electrocardiograms in patients with pericardial effusions typically show diminished QRS amplitude in all leads. A classic but uncommonly seen finding in large effusions with pericardial tamponade is variation in the amplitude of the P wave and QRS complex in successive beats on EKG, referred to as electrical alternans. This finding results from movement of the heart within the pericardial sac. Electrocardiography is not sufficiently sensitive to diagnose pericardial effusions.
Pericardial fluid cytology has an accuracy of 80% to 90% in diagnosing malignant pericardial effusion.[6,28] Lymphomas and mesothelioma have higher false-negative detection rates on cytology evaluation.[6,29] Pericardial fluid cytology has a specificity of up to 100%, but sensitivity ranges from 57% to 100% [Level of evidence: II] in patients with a known cancer diagnosis and pericardial fluid. Because nonmalignant causes of pericardial effusion can occur in 42% to 62% of patients with cancer and pericardial fluid, a negative cytology examination of pericardial fluid does not help distinguish malignant from nonmalignant causes. The use of more than one cytological preparation (such as concentrating the sample via cytospin, using special markers, or analyzing DNA content) increases the yield over a single preparation; however, multiple samples using the same technique did not significantly increase the diagnostic yield in a retrospective study of 215 patients. In a survey of 80 samples, measurement of DNA index via flow cytometry of pericardial fluid has a sensitivity of 94.8% and a specificity of 100%, compared with routine cytology with a sensitivity of 98.5% and a specificity of 92.3%.[Level of evidence: II] Pericardial biopsy may increase the sensitivity of diagnosing pericardial effusions of malignant origin. Because pericardial effusions usually occur in advanced disease and portend a shorter survival than do other sites of metastatic involvement, however, the relief of symptoms rather than diagnosis should be the overriding factor in determining the extent of the evaluation and the course of treatment. Two studies failed to show a difference in survival in cancer patients with pericardial effusion dependent on the results of fluid cytology.[10,32]
No large controlled, randomized, prospective clinical trials demonstrate the optimal management of malignant pericardial effusions or tamponade. Treatment should therefore be individualized to maximize symptom relief with minimal impact on quality of life. Treatment options include percutaneous pericardiocentesis, percutaneous balloon pericardiotomy, pericardial sclerosis, subxiphoid pericardial window, pericardiectomy, or pericardiotomy by thoracotomy or video-assisted thoracoscopy. Considerations in the choice of therapeutic option should include relief of tamponade, minimal invasiveness, cost, morbidity, safety, shortened hospitalization for patients with advanced disease, and the patient's prognosis.[Level of evidence: III]
Large, symptomatic, malignant pericardial effusions are managed by draining the fluid, unless the goals of therapy dictate a less invasive, conservative approach with concomitant shorter survival that should be balanced against quality-of-life concerns. If treatment is indicated for management of tamponade, percutaneous subxiphoid pericardiocentesis is the treatment of choice in the acute setting. Echocardiography is recommended for catheter guidance.[6,34] Catheter drainage is recommended for large effusions to prevent rapid reaccumulation of fluid and subsequent tamponade and for the anticipated survival of the patient.
Recurrent pericardial effusion occurs in 21%  to 50% [33,34] of patients following pericardiocentesis. Limited case series suggest rates of pericardial fluid reaccumulation at 30 days ranging from 5% to 33% after pericardial drainage followed by intrapericardial treatment with sclerosing agents or phosphorus-colloid versus more than 50% of those treated with pericardial drainage alone.[33,34] Treatment options to prevent reaccumulation include intrapericardial sclerosis to obliterate the space within the pericardial sac, or pericardiotomy to increase the quantity of fluid drained from the pericardium. The most effective sclerosing agent for malignant pericardial effusions had been tetracycline, with success rates of up to 80%; however, this agent is no longer available as an intravenous drug in the United States. Alternative sclerosants that have been used include doxycycline, bleomycin, thiotepa,;[Level of evidence: II] carboplatin,[Level of evidence: II] mitoxantrone, docetaxel, and radionuclide chromic phosphate. Most cases may require three or more treatments to achieve adequate sclerosis. Significant pain is reported by 16% of patients undergoing pericardial sclerosis. Consideration must be given to the side effects of various sclerosing agents, e.g., chest pain and arrhythmias. Of patients undergoing pericardial sclerotherapy, 70% to 80% have no fluid reaccumulation within 30 days of the procedure.
A retrospective comparison of pericardiocentesis with sclerotherapy to open surgical drainage among 60 patients showed similar rates for treatment complications, incidence of recurrent effusion, and survival following treatment in both treatment groups. A retrospective review of 59 patients also found similar success rates, whether patients were managed with surgical subxiphoid pericardial window or by pericardiocentesis with or without sclerosis. Patients who underwent pericardiocentesis followed by pericardial window had the longest survival, with a median of 6 months; however, selection bias toward patients with better performance status undergoing more aggressive surgical techniques may contribute to the reported survival advantage. The surgical procedure group had significantly higher average costs of $4,830 compared with $1,625 for patients managed with pericardiocentesis. Other studies have reported mortality, recurrence, and survival rates for sclerosis that are similar to or slightly lower than those for subxiphoid window or video-assisted thoracoscopy.[40,41];[Level of evidence: II][Level of evidence: III] Pericardiocentesis with or without sclerotherapy should be considered instead of more invasive procedures in patients with advanced disease or poor functional status.
Transcutaneous balloon pericardiostomy is another technique that is less invasive than open surgical approaches, which include subxiphoid pericardial windows, thoracotomy with pericardiopleural window formation, and thoracotomy with pericardectomy.
Video pericardioscopy has a diagnostic sensitivity of 97% for detecting malignant effusions. Pericardioscopy also is useful for drainage of loculated effusions.[Level of evidence: II] Video-assisted thoracoscopy is preferable to more invasive surgical management and should be considered for patients requiring repeated pericardiocentesis for control of symptomatic effusions.
Check NCI's list of cancer clinical trials for U.S. supportive and palliative care trials about malignant pericardial effusion that are now accepting participants. The list of trials can be further narrowed by location, drug, intervention, and other criteria.
Superior vena cava syndrome (SVCS) is an array of symptoms caused by the impairment of blood flow through the superior vena cava (SVC) to the right atrium. Symptoms that prompt suspicion of this syndrome include dyspnea, coughing, and swelling of the face, neck, upper trunk, and extremities. In rare instances, patients may complain of hoarseness, chest pain, dysphagia, and hemoptysis. Physical signs that may be noted on presentation are neck vein distention, thoracic vein distention, edema of the face or upper extremities, plethora, and tachypnea. Rarely, cyanosis, Horner syndrome, and a paralyzed vocal cord may also be present.
SVCS is usually a sign of locally advanced bronchogenic carcinoma. Survival depends on the status of the patient's disease. When small cell bronchogenic carcinoma is treated with chemotherapy, the median survival times with or without SVCS are almost identical (42 weeks or 40 weeks, respectively). The 24-month survival rate is 9% in patients without SVCS and 3% in those with the syndrome. When the malignancy is treated with radiation therapy, 46% of patients who have non-small cell lung cancer experience relief of symptoms compared with 62% of patients who have small cell bronchogenic carcinoma. The 2-year survival rate of 5% is almost the same for both groups.
Most non-Hodgkin lymphoma patients with SVCS respond to appropriate chemotherapy or to combined modality regimens.
Etiology and Physiology
Since SVCS was first described by William Hunter in 1757, the spectrum of underlying conditions associated with it has shifted from tuberculosis and syphilitic aneurysms of the ascending aorta to malignant disorders. Almost 95% of SVCS cases described in published modern series result from cancer; the most common cause is small cell bronchogenic carcinoma, followed by squamous cell carcinoma of the lung, adenocarcinoma of the lung, non-Hodgkin lymphoma, and large cell carcinoma of the lung. A nonmalignant cause of SVCS in cancer patients is thrombosis that is associated with intracaval catheters or pacemaker wires. A rare cause of SVCS is fibrosing mediastinitis, either idiopathic or associated with histoplasmosis. Additional rare causes of SVCS include metastatic germ cell neoplasms, metastatic breast cancer, colon cancer, Kaposi sarcoma, esophageal carcinoma, fibrous mesothelioma, Behçet syndrome, thymoma, substernal thyroid goiter, Hodgkin lymphoma, and sarcoidosis.
Knowledge of the anatomy of the SVC and its relationship to the surrounding lymph nodes is essential to understanding the development of the syndrome. The SVC is formed by the junction of the left and right brachiocephalic veins in the mid third of the mediastinum. The SVC extends caudally for 6 to 8 cm, coursing anterior to the right mainstem bronchus and terminating in the superior right atrium, and extends anteriorly to the right mainstem bronchus. The SVC is joined posteriorly by the azygos vein as it loops over the right mainstem bronchus and lies posterior to and to the right of the ascending aorta. The mediastinal parietal pleura is lateral to the SVC, creating a confined space, and the SVC is adjacent to the right paratracheal, azygous, right hilar, and subcarinal lymph node groups. The vessel itself is thin-walled, and the blood flowing therein is under low pressure. Thus, when the nodes or ascending aorta enlarge, the SVC is compressed, blood flow slows, and complete occlusion may occur.
The severity of the syndrome depends on the rapidity of onset of the obstruction and its location. The more rapid the onset, the more severe the symptoms because the collateral veins do not have time to distend to accommodate an increased blood flow. If the obstruction is above the entry of the azygos vein, the syndrome is less pronounced because the azygous venous system can readily distend to accommodate the shunted blood with less venous pressure developing in the head, arms, and upper thorax. If the obstruction is below the entry of the azygos vein, more florid symptoms and signs are seen because the blood must be returned to the heart via the upper abdominal veins and the inferior vena cava, which requires higher venous pressure.
One study suggested that the general recruitment of venous collaterals over time may lead to remission of the syndrome, although the SVC remains obstructed.
Assessment and Diagnosis
Once SVCS is recognized, prompt clinical attention is important. For the following reasons, a diagnosis should be established before therapy is initiated:
In the absence of tracheal obstruction, SVCS is unlikely to be a life-threatening oncologic emergency, and treatment prior to definitive diagnosis is not justified.
The initial evaluation of the patient should include a chest x-ray to look for mediastinal masses and associated findings, such as pleural effusion, lobar collapse, or cardiomegaly. Computed tomography (CT) scanning of the thorax yields the most useful diagnostic information and can define the anatomy of the involved mediastinal nodes. Venous patency and the presence of thrombi are assessed by using contrast and rapid scanning techniques. Depending on local expertise, contrast or nuclear venography, magnetic resonance imaging, and ultrasound may be valuable in assessing the site and nature of the obstruction.
If bronchogenic carcinoma is suspected, a sputum specimen should be obtained. If the sputum specimen is negative, a biopsy specimen should be taken from the most accessible site that is clinically involved with disease. The biopsy approach depends on the working diagnosis, the location of the tumor, the physiologic status of the patient, and the expertise available at the facility. It may include bronchoscopy, biopsy of palpable cervical or supraclavicular lymph nodes, needle biopsy of a lung mass or mediastinal nodes using either CT or ultrasound guidance, mediastinoscopy, mediastinotomy, median sternotomy, video-assisted thoracoscopy, and conventional thoracotomy. The biopsy findings will help the clinician plan appropriate treatment.
The treatment of SVCS depends on the etiology of the obstruction, the severity of the symptoms, the prognosis of the patient, and patient preferences and goals for therapy. Radiation therapy or chemotherapy should be withheld until the etiology of the obstruction is clear. The treatments discussed here focus on SVC obstruction caused by a malignant tumor. Because the treatment of malignant obstruction may depend on tumor histology, a histologic diagnosis—if not made earlier—should be made before treatment is initiated. Unless there is airway obstruction or cerebral edema, there appears to be no detriment in outcome when treatment is delayed for the assessment.[1,11,12,13,14,15] The following treatment approaches can be used for SVCS.
A patient with sufficient collateral blood flow and minimal symptoms may not need treatment. If the lesion is above the azygous vein or if the onset of SVC occlusion is slow enough to allow sufficient collateral circulation, the symptoms and signs may stabilize, and the patient may be comfortable enough to forego further therapy. Short-term palliation of a symptomatic patient who does not want aggressive treatment may be achieved by elevating the head and using corticosteroids and diuresis. There are no definitive studies that prove the effectiveness of steroids, although steroids are potentially useful to treat respiratory compromise. Diuretics may give symptomatic relief of edema but can ultimately cause systemic complications, such as dehydration.[9,16]
If the obstruction of the SVC is caused by a tumor that is not sensitive to chemotherapy, radiation therapy should be given. Treatment with larger fractions of radiation is thought to be beneficial in developing a rapid response. One study shows, however, that there is no obvious need for large radiation fraction sizes for the first few radiation treatments as was previously believed. Many fractionation schemes have been used, with doses ranging from 30 Gy in 10 fractions to 50 Gy in 25 fractions. Relief of symptoms in small cell lung cancer is reported to be 62% to 80%, whereas in non-small cell lung cancer, approximately 46% of the patients experienced symptomatic relief.[2,18] In one study, more than 90% of the patients achieved a partial or complete response with a 3-week regimen of 8 Gy given once a week for a total dose of 24 Gy.
Chemotherapy is the treatment of choice for sensitive tumors such as lymphoma or small cell lung cancer. SVCS does not appear to be an independent prognostic factor, and its presence should not change the treatment approach. Rapid initiation of chemotherapy can result in complete and partial response rates of the SVCS of more than 80% in small cell lung cancer patients.[2,18]
It has been suggested that SVCS arises when a thrombus forms in a partially occluded vein. In patients with a documented thrombus in the SVC, treatment may include thrombectomy, with or without tissue plasminogen activator or other thrombolytic agents such as streptokinase or urokinase.
There have been numerous small studies using an intravascular expandable stent to reopen the occluded SVC; however, no prospectively designed comparative studies have been published. The reported response rates have been about 90% or greater.[Level of evidence: II] There is no agreement on the need for anticoagulant therapy after stent placement. In one series that used anticoagulant therapy for patients as part of the treatment protocol, there were reports of reocclusion after this therapy was stopped.[Level of evidence: II] However, in another study, 17 cancer patients who were treated with stents and who did not have anticoagulant therapy had no occlusions.[Level of evidence: II]
Surgical bypass of an obstructed SVC is more appropriate for patients with a benign obstruction than with a malignant obstruction, although surgical bypass has also been used for patients with malignant obstructions.
Patients and family members are often frightened and anxious because of the symptoms produced by SVCS, particularly swelling, dysphagia, coughing, and hoarseness. Information about the cause of the symptoms and about short-term measures for palliation is needed by patients and family members, especially during the diagnostic period. When aggressive treatment is declined because of the terminal nature of the underlying disease, symptom management approaches may need to be taught to patients and family members.
Because most adult patients who develop SVCS have lung cancer, the treatment and psychologic support approaches that are developed for SVCS should take into account the patient's prognosis and psychologic condition, goals of care, and other symptoms caused by the malignancy.
As described in other sections of this summary, SVCS refers to the symptoms associated with the compression or obstruction of the SVC; the compression of the trachea is termed superior mediastinal syndrome (SMS). Because SMS and the resulting respiratory compromise frequently occur in children with SVCS, the two syndromes have become almost synonymous in pediatric practice.[26,27] In adults, the trachea and the right mainstem bronchus are relatively rigid structures compared with the vena cava, but in children these structures are more susceptible to compression. In addition, the relatively smaller intraluminal diameters of a child's trachea and bronchus can tolerate little edema before respiratory symptoms occur. Because of this accompanying respiratory component, SVCS in children differs from the adult syndrome and constitutes a serious medical emergency.
The most common symptoms of SVCS in children are similar to those in adults and include coughing, hoarseness, dyspnea, orthopnea, and chest pain. Symptoms that are less common but more serious are anxiety, confusion, lethargy, headache, distorted vision, a sense of fullness in the ears, and, especially, syncope.
SVCS is rare in children and appears at presentation in 12% of pediatric patients with malignant mediastinal tumors.[28,29] The etiology, diagnosis, and treatment of SVCS in children differs from that in adults. Whereas the most frequent cause of SVCS in adults is bronchogenic carcinoma, in children the most frequent malignant cause of the syndrome is non-Hodgkin lymphoma. As in adults, a frequent nonmalignant cause is thrombosis from catheterization for venous access.
A physical examination, chest radiograph, and the medical history of the patient are usually sufficient to establish a diagnosis of SVCS. If lymphoma or other malignant disease is suspected, it is desirable to obtain a tissue sample for diagnosis. However, the procedure to obtain the specimen may involve significant risk and may not be clinically feasible. Children with SVCS have a poor tolerance for the necessary general anesthesia because the accompanying cardiovascular and pulmonary changes aggravate the SVCS, often making intubation impossible. Also, extubation may be difficult or impossible, thus requiring prolonged airway provision (intubation). A CT scan of the chest to determine tracheal size, upright and supine echocardiography, and a flow volume loop may help evaluate anesthetic risk. Because anesthesia use is a serious risk, the diagnosis should be made with the least invasive means possible. Published reports suggest a stepwise approach to diagnosis.
When a malignant mass is the cause of the SVCS, the situation may be a medical emergency with no opportunity to establish a tissue diagnosis. In these cases, the most appropriate course may be to initiate empiric therapy prior to biopsy. The traditional empiric therapy is irradiation, with the daily dose governed by the presumed radiosensitivity of the tumor. After irradiation, respiratory deterioration from the apparent tracheal swelling may occur because of the inability of narrow lumens in children to accommodate edema and because of the greater degree of edema at onset, which is the result of the rapid speed at which tumors grow in children. In these situations, a course of prednisone at 10 mg/m2 of body surface area 4 times per day may be necessary.
In addition to radiation, empiric therapy of SVCS has included chemotherapeutic agents incorporating steroids, cyclophosphamide, or both in combination with an anthracycline and vincristine. If the tumor fails to respond, it may be a benign lesion.
If surgery becomes necessary, it should be performed with the patient in the semi-Fowler's position, allowing the surgeon the ability to rapidly change the patient's position to lateral or prone. Cardiopulmonary bypass facilities and a rigid bronchoscope should be available in a standby capacity.
The PDQ cancer information summaries are reviewed regularly and updated as new information becomes available. This section describes the latest changes made to this summary as of the date above.
Dyspnea in Patients With Advanced Cancer
This section was renamed from Dyspnea and Coughing in Patients With Advanced Cancer.
Revised text to state that peripheral and central mechanisms as well as mechanical and chemical pathways are involved with a variety of sensory afferent sources (cited Widdicombe as reference 9, Lee as reference 10, and Undem et al. as reference 11).
Added text about the qualities of dyspnea (cited Parshall et al. as reference 12).
Added text about assessing dyspnea (cited Bausewein et al. as reference 16 and Dorman et al. as reference 17).
Added text to state that functional assessments such as the 6-minute walk test and exercise ergometry may also provide valuable information about the severity and impact of dyspnea (cited American Thoracic Society as reference 19 and ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories as reference 20).
Revised text to include a study of the role of supplemental oxygen in patients without hypoxemia (cited Abernethy et al. as reference 34).
Added text about high-flow oxygen devices and bilevel positive airway pressure (cited Hui et al. as reference 35 and Nava et al. as reference 36).
Added this new section.
Malignant Pleural Effusion
Added a subsection about Chronic long-term indwelling tunneled pleural catheters.
Malignant Pericardial Effusion
Added percutaneous balloon pericardiotomy as a treatment option.
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Purpose of This Summary
This PDQ cancer information summary for health professionals provides comprehensive, peer-reviewed, evidence-based information about the pathophysiology and treatment of cardiopulmonary syndromes, including dyspnea, malignant pleural effusion, malignant pericardial effusion, and superior vena cava syndrome. It is intended as a resource to inform and assist clinicians who care for cancer patients. It does not provide formal guidelines or recommendations for making health care decisions.
Reviewers and Updates
This summary is reviewed regularly and updated as necessary by the PDQ Supportive and Palliative Care Editorial Board, which is editorially independent of the National Cancer Institute (NCI). The summary reflects an independent review of the literature and does not represent a policy statement of NCI or the National Institutes of Health (NIH).
Board members review recently published articles each month to determine whether an article should:
Changes to the summaries are made through a consensus process in which Board members evaluate the strength of the evidence in the published articles and determine how the article should be included in the summary.
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Some of the reference citations in this summary are accompanied by a level-of-evidence designation. These designations are intended to help readers assess the strength of the evidence supporting the use of specific interventions or approaches. The PDQ Supportive and Palliative Care Editorial Board uses a formal evidence ranking system in developing its level-of-evidence designations.
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National Cancer Institute: PDQ® Cardiopulmonary Syndromes. Bethesda, MD: National Cancer Institute. Date last modified <MM/DD/YYYY>. Available at: http://www.cancer.gov/about-cancer/treatment/side-effects/cardiopulmonary-hp-pdq. Accessed <MM/DD/YYYY>.
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