What happened, in summary

A 63-year-old woman was admitted after 3 months of pelvic pain. Ultrasound found a predominantly cystic 12 cm mass involving the left ovary. She underwent total hysterectomy with removal of both ovaries and fallopian tubes. The right adnexa, cervix, and uterus appeared normal, while the left ovarian mass had multiple cystic spaces and a firm 3.5 cm area.

Microscopic review showed a complex mixture of mucinous, endometrioid, and mesonephric-like tissue. A 1.6 cm area had branching papillary, cribriform, and solid growth with increased mitotic activity, supporting mesonephric-like adenocarcinoma. Immunostaining helped distinguish the components: the mesonephric-like areas were positive for CD10, TTF1, and GATA3 and negative for estrogen and progesterone receptors. The overall diagnosis was FIGO stage I ovarian mesonephric-like adenocarcinoma arising in a background of mixed Müllerian proliferations.

Sequencing of the separate tumor components found shared KRAS p.G12A, ARHGAP35, and PPP2R1A mutations with chromosome 1q gain, supporting a common clonal origin rather than separate collision tumors. An IRS1 mutation was limited to the endometrioid and mesonephric-like areas. Together, the shared molecular changes supported a common origin for the different tumor components.