Synchronous Mesonephric-like Adenocarcinoma and Endometrioid Borderline Tumour in Bilateral Ovaries: A Case Report

Mesonephric Like Adenocarcinoma (MLA) is a rare aggressive carcinoma recognised in the 2020 WHO classification, with fewer than 200 cases reported worldwide. It shows KRAS mutations in 70-81% of cases, a strong association with endometriosis (50- 70%), and a characteristic immunoprofile (PAX8+, TTF1+, GATA3 patchy+, ER-, WT1-). The histogenesis of MLA is increasingly linked to Müllerian epithelium, often in association with endometriosis. The coexistence of an MLA and an endometrioid borderline tumour within bilateral ovaries is exceedingly rare and provides further evidence of divergent Müllerian differentiation. This is a case report of a 45-year-old nulliparous woman presenting with abdominal pain and bilateral ovarian masses. Preoperative serum Carcinoembryonic Antigen (CA)-125 was 455 U/mL and CA 19-9 was 346 U/mL. Intraoperative frozen section of the left ovarian mass indicated an epithelial malignancy. Permanent section analysis confirmed MLA in the left ovary (PAX8+, TTF1 strong+, GATA3 patchy+, ER–, WT1–, wild-type p53). The right ovary harbored an endometrioid borderline tumour (PAX8+, ER+, TTF1–, GATA3–, wild-type p53). Endometriosis was concurrently identified in both ovaries and fallopian tubes. The patient underwent complete staging surgery followed by chemotherapy and remains clinically and radiologically disease-free at the time of reporting. This case highlights the critical role of comprehensive immunohistochemical profiling in the precise diagnosis of rare ovarian tumours and provides further evidence supporting a Müllerian origin for MLA.