We report the case of a 57-year-old woman with familial adenomatous polyposis (FAP) who presented with bilateral ovarian microcystic stromal tumors (MCSTs) and a cribriform-morular variant of papillary thyroid carcinoma, as well as concurrent noninvasive endometrial adenocarcinoma. The ovarian masses were confined to the ovaries. The tumor cells were positive for nuclear expression of β-catenin. The papillary thyroid carcinoma revealed the cribriform morular architecture associated with FAP, and immunohistochemistry also showed aberrant nuclear β-catenin. The endometrial adenocarcinoma, in contrast, showed an immunophenotype of negative nuclear β-catenin. Whole exome sequencing of blood was performed, and analysis revealed a rarely reported variant in the adenomatous polyposis coli (APC) gene, c.475dupT(pTyr159Leufs*9). The concurrence of these various neoplasms within one patient could provide insights into the pathogenesis of MCST, which has only recently been described, and underscores the importance of recognizing this rare entity in the setting of FAP.
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