A malignant neoplasm that arises from mesothelial cells in the pleura and shows a diffuse growth pattern. it arises on the parietal and sometimes visceral pleura as multiple small nodules that later become confluent and invade the chest wall adipose tissue and muscle. asbestos exposure is the main cause for the development of pleural malignant mesothelioma. it usually affects patients over sixty years of age. the latency period is long. patients usually present with pleural effusion, dyspnea and chest wall pain. additional signs and symptoms include chills, sweating, weight loss, and weakness. morphologic variants include epithelioid, desmoplastic, sarcomatoid, and biphasic mesothelioma. the clinical course is usually aggressive.