Value of estrogen and progesterone receptor immunostaining in distinguishing between peritoneal mesotheliomas and serous carcinomas

The differential diagnosis between peritoneal mesotheliomas and serous carcinomas involving the peritoneum may be difficult, but it can be facilitated by the use of immunohistochemistry. To determine whether estrogen receptors (ER) or progesterone receptors (PR) may have any value as immunohistochemical markers for discriminating between these malignancies, 40 serous carcinomas of the ovary metastatic to the peritoneum, 7 primary peritoneal serous carcinomas, 30 epithelioid peritoneal malignant mesotheliomas, 5 well-differentiated papillary mesotheliomas, and 4 adenomatoid tumors were immunostained for ER and PR. Reactivity for ER was obtained in 35 (88%) of the metastatic serous carcinomas of the ovary and 6 (86%) of the primary peritoneal serous carcinomas, whereas positivity for PR was observed in 24 (60%) of the metastatic serous carcinomas and 4 (56%) of the primary peritoneal serous carcinomas. None of the mesotheliomas or adenomatoid tumors expressed ER or PR. It is concluded that, because of its high sensitivity for serous carcinomas, ER immunostaining could be very useful in distinguishing between serous carcinomas and peritoneal mesotheliomas. Immunostaining for PR, however, has little practical utility.