Non-endometrioid carcinomas of the uterine corpus: A review of their pathology with emphasis on recent advances and problematic aspects

This review considers the clinical and pathologic features of the various histologic subtypes of endometrial carcinoma excluding those of pure endometrioid type, as the latter tumors were the subject of a previous contribution in the Journal (Vol. 9, No. 2). Non-endometrioid carcinomas, which account for about 10% of endometrial carcinomas, may pose a great array of problems in differential diagnosis, including their distinction not only from benign lesions but also endometrioid carcinoma and various tumors that may secondarily involve the uterine corpus. The most common subtypes are serous, mucinous, and undifferentiated. Rarer tumors are clear cell, squamous, transitional cell carcinomas, and a variety of poorly differentiated carcinomas with unusual forms of differentiation, such as hepatoid carcinoma, carcinomas with trophoblastic elements, and giant cell carcinoma. Mixed carcinomas, which are common, are also discussed, including those with a component of endometrioid carcinoma. The final section deals with endometrial involvement by metastatic tumors, lesions that, albeit rare, are sometimes neglected in the differential diagnosis of endometrial carcinomas. Important aspects emphasized are: (1) The potential for serous carcinoma to be mimicked by various forms of papillary endometrioid carcinoma. (2) The rarity of clear cell carcinoma and the greater frequency of clear cells in endometrioid carcinoma. (3) The frequency of mucinous epithelium in tumors of mixed cell type. (4) The frequency with which neoplastic mucinous epithelium originates from the endometrium. (5) The striking degree of differentiation of some squamous cell carcinomas. (6) The occasional predominance of non-endometrioid carcinomas (especially serous or undifferentiated carcinoma) within malignant mullerian mixed tumors. (7) The spectrum of reactive epithelial changes and other non-neoplastic abnormalities that may mimic serous or clear cell carcinoma.