Müllerian clear cell carcinoma arising from sigmoid endometriosis with pericolic lymph node metastasis in the absence of adnexal disease: a case report

Background: Malignant transformation of endometriosis is rare and most commonly involves the ovary. Extraovarian transformation, particularly in the gastrointestinal tract, is exceptional, and clear cell carcinoma (CCC) arising from intestinal endometriosis is rarely reported. Case presentation: We report a 64-year-old postmenopausal woman with no prior history of endometriosis in whom a sigmoid lesion was incidentally detected during follow-up for a presumed benign ovarian cyst. Colonoscopic biopsy revealed a poorly differentiated carcinoma with clear cell features, and immunohistochemistry (PAX8+, CK7+, HNF1β+, CK20-) supported a Müllerian origin. The patient underwent complete cytoreductive surgery (R0). Final histology confirmed Müllerian clear cell carcinoma arising from sigmoid endometriosis with pericolic lymph node metastasis (pT3N1M0). Integration of the immunophenotypic profile (PAX8+, CK7+, HNF1β+, CK20-), and demonstration of adjacent endometriosis supported the diagnosis of Müllerian clear cell carcinoma arising from endometriosis, fulfilling the Sampson and Scott criteria. She received adjuvant carboplatin and paclitaxel and is disease-free at 6 months. Conclusion: Müllerian CCC arising from intestinal endometriosis is extremely rare and may occur in postmenopausal women without known endometriosis. Accurate immunohistochemical diagnosis is essential to avoid misclassification and guide appropriate oncologic management.