Pathobiology and clinical significance of malignant pleural effusions

Metastatic malignant pleural effusion (MPE) represents advanced-stage cancer and is defined by the establishment of metastatic tumor foci within the pleural space. It is most commonly associated with high degrees of morbidity and mortality. Annually, over 150,000 cancer patients in the United States develop MPE, which is associated with a dismal median survival of 3-12 months. As such, efforts must be made to understand the complex biological factors driving MPE pathophysiology. In this review, we discuss what is currently known and identify knowledge gaps regarding the intrinsic MPE biology of cancer cells and the heterotypic interactions between tumor cells and the immunologic pleural ecosystem. Furthermore, we discuss the clinical opportunities of studying MPE and identify promising directions for MPE research that may lead to a deeper understanding of the disease, ultimately aiming to enhance clinical outcomes for patients with advanced cancer.