Mucinous Adenocarcinoma of the Endometrium

Mucinous adenocarcinoma is one of the least common histologic types of endometrial carcinoma, comprising less than 10% (range 1–9%) of these tumors (Fujiwara and Longacre in Am J Surg Pathol 35:537–544, 2011 [1]; Ross et al. in Am J Surg Pathol 7:715–729, 1983 [2], Melhem and Tobon in Int J Gynecol Pathol 6:347–355, 1987 [3]).While focal mucinous differentiation is a common finding in usual endometrioid endometrial adenocarcinoma (Ross et al. in Am J Surg Pathol 7:715–729, 1983 [2]), mucinous endometrial adenocarcinoma is diagnosed when more than 50% of the tumor cells contain intracytoplasmic mucin (Zaino et al. in Tumours of the uterine corpus. WHO press, Geneva [4]). The diagnosis of endometrial adenocarcinoma in general is based on a combination of cytologic and architectural criteria. For mucinous adenocarcinoma, however, the usual diagnostic criteria cannot always be applied uniformly as cytologic atypia is rarely more than minimal to moderate, and architectural complexity is often the only diagnostic clue. Moreover, rare cases of mucinous adenocarcinoma are histologically similar to non-neoplastic endocervical epithelium or adenocarcinoma of cervical origin. For these reasons, establishing a diagnosis of mucinous adenocarcinoma sometimes poses a diagnostic challenge (Vang and Tavassoli in Int J Surg Pathol 11:261–270, 2003 [5]), requiring immunohistochemical and molecular genetic tests as useful adjuncts. The discussion that follows summarizes the clinical, histopathologic, and molecular genetic characteristics, and the possible precursors of endometrial mucinous adenocarcinoma.