Endocervical-like mucinous borderline tumors of the ovary: clinicopathological features and electron microscopic findings.

Endocervical-like mucinous borderline tumor (EMBT) is a distinct entity of the ovary that seems to be underrecognized. It occurs with relatively high frequency in Japanese women. Compared with intestinal-type mucinous borderline tumor (IMBT), more frequent bilateral occurrence, paucilocular cysts, association with endometriosis, absence of pseudomyxoma but possible association of peritoneal implants and lymph node metastases, and lower mortality rate are the characteristic features. Histologically, it consists of a mixture of two types of epithelium, tall columnar mucinous cells and stratified eosinophilic cells. Electron microscopy revealed that they were endocervical glandlike mucinous cells and ciliated columnar epithelium reminiscent of the fallopian tube. As the mixture of EMBT and serous borderline tumor (seromucinous borderline tumor) occurs, these findings may show that the tumor shows MUllerian origin with two-way differentiation, or differentiation toward endocervical glands with metaplastic features as seen in reactive endocervical lesions.