PT - JOURNAL ARTICLE AU - M Ortega AU - D Benavides TI - 411 Endometrial adenocarcinoma arising from adenomyosis: an unusual case AID - 10.1136/ijgc-2020-IGCS.356 DP - 2020 Nov 01 TA - International Journal of Gynecologic Cancer PG - A171--A171 VI - 30 IP - Suppl 3 4099 - http://ijgc.bmj.com/content/30/Suppl_3/A171.1.short 4100 - http://ijgc.bmj.com/content/30/Suppl_3/A171.1.full SO - Int J Gynecol Cancer2020 Nov 01; 30 AB - Endometrial cancer is the third most common genital malignancy in women. It comprises 3% of cancer-related mortalities. The typical precursor lesion for this is endometrial hyperplasia. Adenomyosis, on the other hand, is a benign uterine pathology that is present in up to 30% of women. There is no clear understanding on how malignant transformation occurs in this condition.This paper presents an unusual case of a 36-year-old Gravida 1 Para 0 (0010), who consulted at the gynecologic emergency room with a chief complaint of vaginal bleeding. She was diagnosed with adenomyosis and endometrial polyps, which were also appreciated sonographically. After failed efforts to address her recurring bleeding over the course of three years, hysteroscopically and medically, she eventually underwent total hysterectomy with bilateral salpingectomy. On histopathologic examination, there were noted foci of endometrioid adenocarcinoma, FIGO grade I, confined within adenomyotic foci with no myometrial invasion. When she consulted at the Gynecologic Oncology Clinic after missing follow-ups, an impression of tumor recurrence was made based on examination and imaging. She was advised for re-exploration for bilateral oophorectomy and tumor debulking, but she opted to forego treatment.The occurrence of such malignancy with a background of a benign lesion is considered rare in literature. This emphasizes the significance of careful histopathologic evaluation, even after a surgery for a supposed benign illness. This also poses the need for further exploration regarding the pathogenesis and clinical course of patients who have this malignant transformation.