Endometrioid Tubal Intraepithelial Neoplasia and Bilateral Ovarian Microcystic Stromal Tumors Harboring APC Mutations: Report of a Case

Microcystic ovarian tumor of the ovary is a neoplasm of presumed stromal derivation characterized by CTNNB1 or APC alterations leading to nuclear β-catenin expression. This tumor has been described as unilateral and indolent in previously published series. The recently characterized endometrioid tubal intraepithelial neoplasia (eTIN) is an epithelial proliferation of the tube also characterized by nuclear β-catenin staining, and distinct from high-grade serous precursors. Herein, a case of bilateral ovarian microcystic stromal tumors and multiple left tubal eTINs discovered incidentally in a 41-yr-old woman with previous history of colon cancer is described. Both ovarian and tubal proliferations harbored APC inactivating mutations. Although history of familial adenomatous polyposis or a germline defect could not be confirmed, the history of colon cancer at a young age and the shared APC mutation in both microcystic stromal tumor and eTIN were suggestive of this possibility. Microcystic stromal tumor has been described in the setting of familial adenomatous polyposis syndrome. This case adds to this association by documenting for the first time bilateral ovarian involvement by microcystic stromal tumor. Moreover, it alerts to the possibility of endometrioid neoplasia of the fallopian tube secondary to APC mutations, a previously undescribed phenomenon.