Malignant Mesothelioma In Situ: A Controversial Diagnostic Entity – A Review

Malignant mesothelioma is a rare aggressive malignancy of serosal surfaces that is strongly associated with exposure to asbestos. The pathological diagnosis of malignant mesothelioma can be difficult to distinguish from reactive benign hyperplasia. Mutations in BAP-1 and CDKN2a distinguish mesothelioma from reactive hyperplasia. An in situ growth phase of mesothelioma until recently was difficult to ascertain due to limits of histological assessment and because mesothelioma tends to spread diffusely along serosal surfaces making sampling for invasion impossible without extensive resection. The current WHO classification of thoracic tumors recognizes mesothelioma in situ as a distinct entity based on histological, genetic, and clinical features. This chapter reviews the topic and concludes that the diagnosis of malignant mesothelioma in situ should be limited to patients eligible for radical resection to confirm the putative diagnosis.