Minimal uterine serous carcinoma with extrauterine tumor of identical morphology: an immunohistochemical study of 13 cases.

Minimal uterine serous carcinoma includes endometrial intraepithelial serous carcinoma and superficial invasive serous carcinoma. Although they represent in situ and early invasive serous carcinomas, more than 50% of them present with extrauterine tumors of identical morphology. It has not been completely clear whether the extrauterine involvement represents a synchronous tumor arising independently or a metastatic lesion from the endometrial primary. To investigate the relationship between the extrauterine tumor and minimal uterine serous carcinoma, 13 cases of such condition were studied by histologic examination and immunohistochemical staining of 5 related protein markers: estrogen receptor, progestin receptor, p53, WT1, and Ki-67. Morphologic assessment of all extrauterine tumors showed similar histologic features to their corresponding endometrial minimal serous carcinomas. Immunostaining revealed almost identical patterns of 5 protein markers with similar intensities between the endometrial tumors and their corresponding extrauterine lesions. WT1 nuclear staining was observed in most of our cases indicating WT1 expression is not a specific marker in distinguishing ovarian serous carcinoma from uterine serous carcinoma. In conclusion, our findings support the hypothesis that a transtubal metastatic process is responsible for the extrauterine involvement by minimal endometrial serous carcinoma.