Seromucinous component in endometrioid endometrial carcinoma as a histological predictor of prognosis

OBJECTIVE In 2014 World Health Organization criteria, seromucinous carcinoma was defined as a new histological subtype in ovarian carcinomas, but "seromucinous carcinoma" was not defined in endometrial carcinomas. The aim of this study was to identify seromucinous carcinoma resembling ovarian seromucinous carcinoma in endometrial carcinomas, and to evaluate the clinical significance for prognoses of the patients. METHODS Central pathological review was conducted for patients with endometrioid carcinoma of the endometrium treated by primary surgery at our hospital between 1990 and 2013. RESULTS Among 340 cases included in the study, no case had all tumor cells resembling ovarian seromucinous carcinoma in all specimens, and 31 cases (9.1%) had seromucinous component in combination with endometrioid carcinomas. Immunohistochemical analysis revealed seromucinous component had positive reactivity for cytokeratin (CK) 7, and negative reactivity for CK20 and caudal type homeobox 2 (CDX2) in all cases. Seromucinous component showed lower immunoreactivity of estrogen receptor and progesterone receptor, compared with endometrioid carcinoma component. Progression-free survival of the cases with seromucinous component was better than those without seromucinous component (p=0.049). CONCLUSION Seromucinous component was identified in approximately 10% of endometrioid carcinoma, and could be a histological predictor for prognosis.