単純子宮全摘および両側付属器摘出術後に膀胱病変として発見された膀胱子宮内膜症の悪性転化の1例

Bladder endometriosis is a rare manifestation of pelvic endometriosis, accounting for approximately 0.9% of all cases. Malignant transformation of endometriosis is uncommon, and bladder involvement is exceedingly rare. We report a case of malignant transformation of bladder endometriosis after hysterectomy and bilateral salpingo-oophorectomy for adenomyosis and ovarian endometriotic cysts. A 51-year-old woman with a long history of endometriosis and previous hormonal therapy for breast cancer developed a rapidly enlarging bladder mass several months after discontinuation of dienogest. Magnetic resonance imaging revealed a lesion on the left posterior bladder wall, and partial cystectomy with omentectomy and ureteral reconstruction was performed. Histopathological examination demonstrated coexisting endometriotic and endometrioid carcinoma components within the same specimen, fulfilling Sampson’s three criteria for malignant transformation. The patient received six cycles of adjuvant chemotherapy with paclitaxel and carboplatin and has remained disease-free for four years. Malignant transformation of bladder endometriosis is an extremely rare condition, and its optimal management has not been established. This case will suggest treatment for malignant transformation of bladder endometriosis.