We report a case of adenomyoma of endocervical type arising in a 44-year-old female. Grossly, a well-circumscribed tumor protruding from the right side of the uterine cervix was seen which was assumed to be an ovarian tumor by imaging studies carried out preoperatively. The tumor was
composed of a mixture of proliferating glands of endocervical type and fascicles of smooth muscle cells. There was no distinct nuclear anaplasia in the proliferating glands, there were no architectural abnormalities, and there was no evidence of destructive stromal invasion such as desmoplasia.
Minimal deviation adenocarcinoma, which shows a gastric phenotype with immunoreactivity for M-GGMC-1 and predominantly PAS-positive neutral mucin, was a serious diagnostic possibility, but the lesion was well-circumscribed, cytologic and architectural abnormalities were absent, and staining
for M-GGMC-1 was negative, which suggested a diagnosis of endocervical adenomyoma. An increased Ki-67 labeling index by up to 20%, the presence of predominantly PAS-positive neutral mucin, and membranous immunoreactivity for CEA in limited areas were diagnostic pitfalls, which could lead to
an erroneous diagnosis of minimal deviation adenocarcinoma of the uterine cervix. Therefore, the results of these ancillary techniques should be interpreted with caution and combined with gross and light microscopic features.