Small cell carcinoma in endometrium on the base of extensive adenomyosis: differential diagnosis with immunochemistry

Small cell carcinomas (SCCs) are rarely seen in the endometrium and usually present as a component of a combined tumor consisting of more differentiated endometrial tumors. SCCs commonly represent the deeply invasive and aggressive component of the tumor, and differentiating SCC from counterparts has a great importance in terms of different treatment modalities and worse prognosis. Differential diagnosis includes distinct tumors indistinguishable from SCC by histologic and morphologic features, and the definite diagnosis requires immunohistochemical proof of diffuse neuroendocrine differentiation. We present a case of combined endometrial tumor composed of SCC, endometrioid adenocarcinoma, and serous carcinoma, which was initially misdiagnosed as carcinosarcoma at another institute, and discuss the differential diagnosis in terms of clinicopathologic features.