Benign multicystic mesothelioma with concurrent colonic adenocarcinoma: a report of two cases.

Benign multicystic mesothelioma (BMM) is a rare tumoral lesion of the peritoneum often discovered incidentally upon surgery, laparoscopy, or radiographical imaging in females of childbearing age. The etiology and question as to whether these lesions occur via a neoplastic or reactive process still remain unknown. In this report, we present two cases of BMM detected in females with concurrent colonic adenocarcinoma arising in the ileocecal region. The tumors were present in the serosa surrounding the colonic adenocarcinoma in one case, and in the omentum in the other case, which grossly mimicked peritoneal seeding of carcinoma. An immunohistochemical analysis revealed that the cells lining the cystic spaces in both lesions were positive for keratin and calretinin, confirming their mesothelial origin. To the best of our knowledge, these cases represent the first documented examples of multicystic mesothelioma concurrent with colonic adenocarcinoma.