Endometriosis as a Silent Emerging Malignant Threat in Young Women: A Case Report of Rare Rapid Transformation of Abdominal Wall Endometriosis Into Mixed High-Grade Serous and Clear Cell Carcinoma One Year Following Cesarean Section.

Abdominal wall endometriosis most commonly occurs in cesarean section (CS) scars. Although malignant transformation is rare, clear cell carcinoma (CCC) is the most commonly reported histological subtype. We present an unusual case of rapid malignant transformation into mixed high-grade serous and CCC within one year following CS. A 34-year-old para 1 woman presented with a two-month history of progressive shortness of breath, abdominal distension, abdominal pain, weight loss, and reduced appetite. Computed tomography (CT) demonstrated extensive peritoneal disease with bilateral ovarian lesions suspicious for advanced gynecological malignancy. She had a known history of endometriosis and had undergone a category 2 CS one year earlier, during which extensive pelvic endometriosis and decidualization were identified intraoperatively. Peritoneal biopsy performed at that time confirmed benign endometriosis without evidence of malignancy. Subsequent magnetic resonance imaging (MRI) demonstrated uterine scar endometriosis, abdominal wall scar endometriosis, and superficial ovarian endometriosis. Further investigations revealed malignant ascitic cytology consistent with metastatic high-grade serous carcinoma of gynecological origin. Diagnostic laparoscopy demonstrated extensive adhesions, ascites, diffuse peritoneal inflammatory disease, and complete obliteration of the pelvic anatomy. Histopathological analysis of biopsies obtained from the pelvic soft tissue, endometrioma cyst wall, and peritoneum confirmed mixed high-grade serous and CCC arising in a background of endometriosis. Following multidisciplinary team discussion, the patient underwent extensive cytoreductive surgery, including total abdominal hysterectomy, bilateral salpingo-oophorectomy, peritonectomy, bilateral ureterolysis, pelvic lymph node excision, and infracolic omentectomy. She was subsequently diagnosed with stage IIIA2 ovarian mixed high-grade serous and CCC and commenced adjuvant chemotherapy with carboplatin and paclitaxel. This case highlights the potential for rare, aggressive, and rapidly progressive malignant transformation of endometriosis, including transformation into mixed histological subtypes, in young women of reproductive age. Clinicians should maintain a high index of suspicion in patients with endometriosis who present with new systemic symptoms, ascites, or rapidly progressive pelvic or abdominal disease.