Abstract
Well-differentiated papillary mesothelioma is a rare tumor occurring predominantly in the peritoneum of young women, a few with history of asbestos exposure. A 28-year-old woman presented with ascites and pain abdomen. Ultrasonography and computed tomography scan of the abdomen revealed a mass in the retroperitoneum measuring 15 cm × 12 cm. Histopathological examination along with immunohistochemistry (IHC) confirmed it to be a papillary mesothelioma in the peritoneum. It is difficult to differentiate from more common malignant mesothelioma and papillary adenocarcinoma, which also have poorer prognosis. The difficulty can be resolved by clinico-radiological correlation along with histopathological examination and IHC.