Case Report: Malignant transformation of deep infiltrating endometriosis: a report of two cases and literature review.

Deep infiltrating endometriosis (DIE) is a severe form of endometriosis that rarely undergoes malignant transformation, and when it does, diagnosis is often difficult. Here, we report two cases of long-standing DIE that progressed to endometrioid adenocarcinoma. The first case involved a 44-year-old woman with pelvic DIE complicated by hydronephrosis, who underwent radical surgery with ureteroneocystostomy. Postoperative pathology confirmed well-differentiated endometrioid adenocarcinoma, and she remained disease-free after receiving chemotherapy and targeted therapy. The second case was a 47-year-old woman with an 18-year history of dysmenorrhea and chronic pelvic pain, also complicated by hydronephrosis. Surgical exploration revealed extensive pelvic adhesions and DIE lesions, and pathology confirmed endometrioid adenocarcinoma. She received postoperative chemotherapy, including an antibody-drug conjugate, and showed no evidence of recurrence during follow-up. A review of the literature identified 57 additional reported cases of malignant transformation arising from DIE, most commonly involving the rectosigmoid colon, vagina, and ureter. Endometrioid adenocarcinoma was the most frequently observed histological subtype. Due to its nonspecific clinical manifestations and overlap with benign DIE, diagnosis remains challenging. Current evidence supports a multidisciplinary approach combining complete surgical resection with adjuvant therapy. Clinicians should remain aware of the rare but possible malignant potential of DIE to facilitate earlier diagnosis and appropriate management.