2021 Oct 8. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan–.
Malignant pleural effusion is characterized by the presence of malignant cells in the pleural fluid. The presence of MPE denotes systemic dissemination of cancer and has been staged as M1a disease, as per the American Joint committee on Cancer TNM staging system. The identification of malignant cells in pleural lavage fluid, performed in patients without a coexistent pleural effusion, has been identified as an indicator of micro-metastatic disease and associated with a higher recurrence rate and poorer survival. Both the parietal and visceral pleura may be involved by the tumor directly or via the blood-borne spread. While the parietal pleura may be involved by secondary spread from the visceral pleura, direct seeding has also been described.
The pathophysiology is attributed to a disturbance of the Starling forces that govern and dictate fluid biomechanics within the pleural space. While pleural fluid production is governed by the difference in the hydrostatic and oncotic pressure between the pulmonary circulation and pleural space, absorption is determined by lymphatic vessels in the parietal pleura. Excess fluid may accumulate as a result of an inability to drain the fluid from the pleural space, which has been postulated to arise as a result of the clogging of the stomata within the parietal pleura or metastatic involvement of hilar and mediastinal lymph nodes.
Lung cancer, breast cancer, and hematological malignancies are the major malignancies associated with direct, contiguous, or hematogenous pleural involvement. From 50 to 55 percent of patients with pleural involvement develop effusion. Wet pleural involvement is associated with a poorer prognosis (as compared to dry pleural disease). Between 42 and 77 percent of effusions in cancer patients have been documented to be exudative in nature. There has been a gradual increase in the incidence of eosinophilic pleural effusions (defined as exudative pleural effusions containing more than 10 percent eosinophils), which can be attributed to a malignant etiology in recent years, with an attempt to delineate malignant eosinophilic pleural effusion as a separate entity. While malignant involvement of the pleura may be one cause of effusion in a patient with cancer, other etiologies also need to be considered among the differential.
Malignant pleural effusions must be differentiated from paramalignant pleural effusions, which are not caused by direct pleural involvement by the tumor. A trapped lung is an entity characterized by the failure of a chronically non-expanded lung to re-expand following drainage of the pleural fluid, which may be caused by extensive involvement of the visceral pleura. Septated Pleural effusions which are characterized by the development of septated fibrin pockets, may represent an underlying cause of failure to achieve successful drainage and complete resolution of dyspnea.
The treatment of recurrent malignant pleural effusions represents a significant financial burden. Dyspnea is the most common presenting complaint associated with the development of pleural involvement by the tumor. Goals of management include palliation of symptoms, with minimal impact on the quality of life while ensuring cost-effectiveness of the treatment.
Therapeutic approaches vary widely given the broad range of treatment options. However, there has been a concerted effort in recent times to move towards patient-related outcomes compared to successful pleurodesis as markers of successful palliation. The role of vascular endothelial growth factor and host-tumor cell interactions in the pleural microenvironment (consisting of inflammatory, mesothelial and endothelial cells) has been the subject of growing scrutiny. Novel immunotherapy approaches have been targeted towards understanding the role of the CD8+ T-cell response and the associated immune responses to translocated microbial pathogens in the pathogenesis of this condition.