Distinct Immunophenotypic Features of Ovarian Microcystic Stromal Tumor

Ovarian Microcystic Stromal Tumor (MCST) is a newly recognized entity with only 19 reported cases, in which only 3 cases showed a solid growth pattern and 1 with concurrent endometrial carcinoma. Recent studies suggested the involvement of the Wnt/β-catenin pathway in MCST tumorigenesis through mutated β-catenin. Here we report another MCST case with a solid growth pattern, distinct immunophenotypes including β-catenin and cyclin D1 (a known β-catenin regulated oncogene), and a coexisting endometrial carcinoma. Macroscopically, the tumor was a well-circumscribed, solid mass. Microscopically, it consisted of predominantly lobulated cellular nodules separated by hyalinized fibrous stroma. Immunophenotypically, the tumor was diffusely and strongly positive for CD10, β-catenin (nuclear) and cyclin D1, and completely negative for inhibin, calretinin, ER, PR, cytokeratins, EMA and c-Myc. To our knowledge, this is the first report to demonstrate the co-over expression of β-catenin and cyclin D1 in case with MCST and concurrent endometrial carcinoma, which may provide new insights to the tumor biology.