Mucinous cystadenoma coexisting with adult granulosa cell tumor in the ovary: is it a composite tumor or heterologous mucinous elements in a granulosa cell tumor?

We herein report a rare tumor combination of mucinous cystadenoma and an adult granulosa cell tumor in the same ovary of a 50-year-old woman. Ultrasound examination showed a multicystic mass in the left ovary. Histologically it showed 2 components that were intimately admixed. One was composed of cysts lined by mucinous epithelium of the intestinal type that was strongly positive for cytokeratin-20 and cytokeratin-7. The other was a granulosa cell tumor of the adult type in which the tumor cells showed microfollicular, sheets, and trabecular patterns. They were positive for calretinin, α-inhibin, and CD99. There are many theories for the histogenesis of such a combination. After discussing all the possibilities we conclude that the mucinous component is probably a heterologous mucinous differentiation within an adult granulosa cell tumor because of the intimate admixture of the 2 components and the mucinous epithelium being of the intestinal type.