Primary testicular microcystic stromal tumor: two case reports with a broad morphological spectrum and frequency of predilection site

Abstract

Background The microcystic stromal tumor (MCST) is a rare neoplasm included in the category of pure stromal tumors of the ovary. Only two cases were previously reported to occur in the testis. Here, two additional cases of testicular MCST presented with clinicopathological manifestation, immunohistochemical profile and genomic analysis. Materials and methods Retrospectively, detailed data on these cases were collected by morphological observation, immunohistochemistry staining (IHC) and next-generation sequencing (NGS) test. Results The two patients aged 31 and 34 years found accidentally a solid mass of 2.1 cm and 1.7 cm in diameter on radiological images. Microscopically, the tumors showed nodular or lobular growth arranged in a variety of structures, such as microcystic, solid, macrocystic or cords, mixed with hyalinization stroma in variable proportions. No atypical mitotic figure or necrosis was observed. Immunohistochemically, both were strongly positive for β-catenin (nuclear and cytoplasmic staining), CD10 and CD99, while negative for α-inhibin and calretinin. NGS analysis revealed missense mutation in exon 3 of CTNNB1. They were disease-free 30 to 45 months after initial diagnosis. Conclusion The MCST, particularly in testis, is extremely rare and characterized by classical morphology. Our findings indicate that the MCST would have broader morphological spectrum but relatively constant immunophenotypes and molecular events to those of ovarian tumors reported.