Malignant mesothelioma in rare sites: two case reports.

Mesothelioma is a rare tumor originating from mesothelial cells in the pleura or other sites. Malignant pleural mesothelioma (MPM) is the most common aggressive type of mesothelioma (accounting for 81%) and carries a poor prognosis (median OS: 1 year). Diagnosing diverse histologic types is challenging. We report two cases: a 72-year-old female with peritoneal mesothelioma demonstrated a remarkable response, with the lesion shrinking from 150×160mm to radiologically undetectable after chemo-immunotherapy, resulting in a sustained complete response. Conversely, a 66-year-old male with MPM exhibited primary platinum resistance, progressing after first-line pemetrexed/lobaplatin and subsequent second-line chemotherapy. Peritoneal mesothelioma responded better to immuno-chemotherapy, while MPM showed platinum resistance. These contrasting disparate outcomes underscore that precise pathology and individualized treatment based on anatomic site are crucial, suggesting that malignant pleural and peritoneal mesothelioma may represent distinct clinical entities.