Etiopathogenesis of malignant pleural effusion

: Malignant pleural effusion (MPE) is featured by containing malignant cells. It is a frequent finding in patients with metastatic disease and it develops in 15% of patients with malignant disease. Two-thirds of all cases have a pleural effusion as one or sole initial manifestation of malignant disease. Primary tumors that most frequently develop MPE are lung, breast cancer, and lymphoma accounting for 75% of all cases. A MPE can develop in primary or metastatic malignancies of the pleura by spreading of malignant cells within the intrapleural cavity and into lymphatics causing their obstruction. The otherwise physiologic balance between the secretion of fluids into the pleural space and its reabsorption is largely disturbed by the occurrence of a MPE. Malignant cells can enter the pleural space via the hematogenous, direct or lymphatic spread. Direct tumor involvement of pleura can lead to a pleural fluid accumulation by increasingly producing the liquid and thus influencing the normal parietal pleural lymphatic functioning. Tumor may extensively infiltrate pleural capillaries, leading to increased filtration, or may produce different cytokines that increase capillary permeability, while decreased plasma osmotic pressure or decreased pleural pressure can contribute to the enhanced entry of liquid as well. On the other hand, tumor growth infiltrating the draining lymphatics or lymph nodes may block the lymphatic drainage thus decreasing the absorbtion rate of pleural fluid, with the subsequent accumulation of fluid in the pleural space, while different extrinsic factors including limited respiratory mobility, mechanical compression of lymphatics with blockage of their stomata, may be responsible in the cases when lymphatics activity is significantly disturbed, but not due to direct damage of the vessels. With the advancements in molecular medicine, the impact of tumor-host cell interactions has been recognized as an important pathogenesis mechanism in development of MPE.