The Rarest of the Rare: A Case of BAP1-Mutated Primary Peritoneal Mesothelioma.

Malignant mesotheliomas (MM), as described are rare tumors that are mostly associated with occupational exposure to asbestos. They most commonly occur in the pleura. Other unfamiliar sites where they can occur are the peritoneum, pericardium, and tunica vaginalis. There is no significant correlation between the amount and duration of asbestos exposure to mesothelioma development as reported by various studies over the years. Apart from the environmental exposure, the development of malignant mesothelioma has been linked to a mutation in the BAP1 gene, which can predispose the patient to develop other malignancies associated with BAP1 mutation. We report a case of a 43-year-old man without any significant risk factors, who presented with a complaint of abdominal discomfort and was found to have malignant peritoneal mesothelioma (MPM). With a known familial history of mesothelioma and melanoma, our patient underwent genetic testing which revealed a mutation in BAP1, affirming the strong association with the development of MPM. Young patients who develop malignant mesothelioma without risk factors for MM should have germline testing for BAP1. This case report is unique and highlights a familial variant of mesothelioma, even rare with peritoneal mesothelioma in our patient.