Endometrial adenocarcinoma involving adenomyosis without true myometrial invasion is characterized by frequent preceding estrogen therapy, low histologic grades, and excellent prognosis.

We reviewed cases of endometrial adenocarcinoma to characterize the carcinomas that involved foci of adenomyosis in contrast to the carcinoma that invaded into the myometrium. We encountered 18 cases in which tumor involved foci of adenomyosis without myometrial invasion. There were no cancer-related deaths in these 18 cases over a minimum follow-up period of 5 years. Myometrial invasive tumor was present in 43 cases. Eight of these 43 patients died within 5 years. History of postmenopausal use of estrogen of longer than 6 months duration was obtained in 9 of the 18 patients (50%) with carcinoma confined to adenomyosis compared with 8 of the 43 (19%) with myometrial invasive carcinoma. Only 1 of the 18 cases with adenocarcinoma involving adenomyosis had architectural or nuclear grade III carcinoma compared to 12 of the 43 patients with myometrial invasive carcinoma. Adenocarcinomas involving adenomyosis were characterized by frequent preceding estrogen use, low histologic grades, and excellent prognosis.