Ovarian microcystic stromal tumor: Review of a rare entity with recent updates

Microcystic stromal tumors (MCSTs) are rare ovarian stromal tumors. They harbor CTNNB1 or APC mutations, resulting in β-catenin nuclear expression. Morphologically, they characteristically consist of tumor cells with small round nuclei, inconspicuous nucleoli, moderate amount of eosinophilic or vacuolated cytoplasm. Cells can form solid nests and sheets, small or sometimes large cystic structures. Background stroma is often myxoid with foci of fibrosis. In addition to the nuclear β-catenin stain, the tumor cells are characteristically negative for inhibin and calretinin, but positive for CD10, CyclinD1, WT1 and FOXL2. To date, all MCST cases treated with oophorectomy or more extensive surgery have followed benign clinical courses. However, two of the four cases treated with ovarian cystectomy/tumor resection recurred in the residual ovary and local extraovarian involvement several years after ovarian cystectomy, which indicates MCST has the potential to recur and spread locally. This article is aimed to review the literature about MCST to summarize its morphology, immunophenotype, molecular alteration as well as clinical behavior.