It is usually caused by disturbance of the normal Starling forces regulating reabsorption of fluid in the pleural space, via obstruction of mediastinal lymphatics draining the parietal pleura. Tumors that metastasize frequently to these nodes, i.e. lung cancer, breast cancer, and lymphoma, cause most malignant effusions.
Pleural effusion restricts ventilation and causes progressive shortness of breath.
Pleural deposits of tumor cause pleuritic pain. Lymphangitic pulmonary metastases further worsen pulmonary function. Management is usually complicated by the presence of disseminated tumor, with bone, brain and other organ metastases. In addition, the patient is often malnourished and debilitated. Untreated, death usually ensues within a few months due to the primary disease or to complications related to the effusion.