Multiple focal extraovarian serous carcinoma.

Nine cases of multiple focal extraovarian serous carcinoma were studied, and their gross, light microscopic, and ultrastructural features were compared with those of three serous ovarian tumors and three malignant mesotheliomas. On light microscopy, the multiple focal extraovarian serous carcinoma shared many features of the serous ovarian tumors. However, they also displayed some ultrastructural features shared by both serous ovarian tumors and malignant mesotheliomas, and other features more specific for malignant mesotheliomas. We concluded that the multiple focal extraovarian serous carcinomas probably arise from mesothelial cells modified by various müllerian influences and should be classified separately from the other two entities.