Endometrial Carcinoma Arising in Adenomyosis in the Myometrium with Uninvolved Endometrium: A Case Report.

Endometrial carcinoma arising in adenomyosis (EC-AIA) is a rare entity that originates deep within the myometrium and often spares the endometrial lining. We report a 53-year-old woman who presented with a vascularized uterine mass invading the bladder (International Federation of Gynecology and Obstetrics [FIGO] stage ⅢB2). Despite imaging findings suggesting malignancy, endometrial curettage yielded only atrophic cells, and hysterectomy confirmed a histologically normal endometrial cavity. Final pathology revealed endometrioid adenocarcinoma confined to adenomyotic lesions with lymph node involvement. This case underscores a critical diagnostic pitfall: negative endometrial sampling does not exclude EC-AIA. Moreover, applying current FIGO staging systems, designed for endometrial-origin tumors, to EC-AIA presents significant limitations, risking either underestimation of deep invasion or artificial upstaging.