Primary squamous carcinoma of the ovary likely arising from a monodermal cystic mucinous teratoma.

We present a 58-year-old woman with primary squamous carcinoma of the ovary likely arising from a monodermal cystic mucinous teratoma. Noninvolved ovary showed no Brenner tumor, endometriosis, transitional carcinoma, endometrioid adenocarcinoma, or typical multigerm layer classic mature teratoma. Moreover, no other primary site was possible because there were no prior or concomitant squamous carcinomas, or history of cervical intraepithelial neoplasia. The tumor showed strong positivity for p63 and CK5/6, reactivity that also extended from the squamous carcinoma into the basal-cell lining of the mucinous cyst of a likely monodermal teratoma. This basal-cell pattern was absent in a series of conventional benign and borderline cystic mucinous cystadenomas of the ovary, but clearly present in the mucinous cysts part of mature teratomas. We present this as a unique case of squamous carcinoma likely arising from a monodermal cystic mucinous teratoma. Moreover, we submit that the p63 and CK5/6 staining pattern may help to differentiate monodermal cystic mucinous teratoma from conventional cystic mucinous tumors.