Ovarian Mesonephric-Like Adenocarcinoma Arising from an Endometriotic Cyst with an Identical <i>KRAS</i> Mutation in Both Components: A Case Report

Mesonephric-like adenocarcinoma (MLA) is a rare tumor that occurs in the uterine corpus and ovary. It shares the morphological and immunohistochemical features of cervical mesonephric adenocarcinoma. Recent reports have suggested that a majority of ovarian MLAs are associated with endometriosis. Herein, we report the novel tumor of a 54-year-old Japanese woman with a history of bilateral ovarian endometriotic cysts who presented with abdominal distension. Pelvic magnetic resonance imaging revealed a 14-cm left ovarian cystic tumor with an intra-cystic solid mass. Histological examination revealed proliferation of columnar or cuboidal tumor cells forming round tubules, irregular tubular glands, fused glands, papillary structures, and solid nests.Additionally, associated endometriosis was observed in the cyst wall. The tumor cells were diffusely positive for GATA-binding protein 3 (GATA3) and negative for estrogen receptor. The tumor cells also showed wild-type p53, with retained expression of AT-rich interactive domain-containing protein 1A (ARID1) and phosphatase and tensin homolog (PTEN). Molecular analysis revealed an identical <i>KRAS</i> p.G12V mutation in the tumor and the endometriotic cyst. The present tumor elucidates the pathogenesis and molecular mechanisms of ovarian MLA and demonstrates that ovarian MLA is an endometriosis-associated neoplasm. Further investigation into the pathogenesis and molecular mechanisms of ovarian MLA may assist in identifying potential therapeutic targets for this rare condition.