Malignant mesothelioma of the peritoneum: case reports and immunohistochemical findings including Ki-67 expression.

A malignant mesothelioma (MM) is an aggressive neoplasm, although some patients have shown long-term survival, and factors related to survival remain uncertain. We present three cases of MM of the peritoneum including autopsy results, in which factors related to long-term survival were investigated. Case 1 was a 69-year-old man who died 6 years after the initial diagnosis. In case 2, a 67-year-old woman came to us with abdominal distention and, despite chemotherapy, died 9 months after the initial diagnosis. The patient in case 3 was a 68-year-old man who also had abdominal distention and died 9 months after the initial diagnosis. We studied the clinicopathological appearance and performed immunohistochemical staining including Ki-67 labeling index (Ki-67 LI) in primary and metastatic sites of these cases. The histological findings of case 1 indicated epithelioid type; case 2 and 3 were of biphasic type. Immunohistochemical results were consistent with MM. The Ki-67 LI value for both primary and metastatic sites of case 1 was significantly lower than those in cases 2 and 3. We consider Ki-67 LI to be a useful prognostic indicator for MM of the peritoneum.