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A malignant pleural effusion is diagnosed by detecting exfoliated malignant cells in pleural fluid or demonstrating these cells in pleural tissue obtained by percutaneous pleural biopsy, thoracoscopy, thoracotomy, or at autopsy. In a number of patients, even though the pleural effusion is caused by the malignancy, neoplastic cells cannot be detected in pleural fluid or pleural tissue and, in fact, probably are not present in these tissues. It is logical to categorize these pleural effusions associated with malignancy, in which there is no direct pleural involvement with tumor and no other cause for the effusion is found, as paramalignant effusions (Table 77-1). Lymphatic obstruction appears to be the most common mechanism for the development of a paramalignant effusion. Other local effects of the tumor causing a paramalignant effusion are bronchial obstruction resulting in pneumonia or atelectasis. Furthermore, it is important for the clinician to recognize that effusions can result from systemic effects of the tumor and adverse effects of therapy.

Table 77-1Causes of Paramalignant Pleural Effusions

The presence of a malignant pleural effusion secondary to lung cancer portends a poor outcome.1 Similarly, a malignant effusion secondary to a nonlung primary is a manifestation of far advanced disease and is associated with limited survival.

Malignancies Associated with Pleural Effusions

Carcinoma of any organ can metastasize to the pleura. However, carcinoma of the lung is the most common malignancy to invade the pleura and produce malignant and paramalignant effusions (Table 77-2). Carcinoma of the breast is second in incidence and, in some populations, exceeds lung cancer as a cause of malignant effusions. Together, both malignancies account for 65% of all malignant pleural effusions.2 After lung and breast cancer, the frequency declines markedly, with ovarian and gastric cancer representing up to 5% of malignant pleural effusions. Lymphoma accounts for approximately 10% of all malignant pleural effusions and is a common cause of chylothorax. Carcinomas of the lung, breast, ovary, and stomach and lymphomas account for about 80% of all malignant pleural effusions. In approximately 7% of ...

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