[Clinicopathologic and molecular characterizations of Sertoli cell tumor, not otherwise specified of the testis]

Objective: To investigate the histomorpholgic spectrum, immunophenotypic, and molecular genetic features of Sertoli cell tumor, not otherwise specified (SCT, NOS) of the testis. Methods: Seven cases of SCT, NOS of the testis were analyzed(4 from Peking University Third Hospital and 3 from Zhejiang Provincial People's Hospital) between 2008 and 2017. The histopathologic features were examined based on HE staining, and EnVision method was used for immunohistochemistry staining of calretinin, inhibin, β-catenin, cyclinD1, CD10, CKpan, neuroendocrine markers, WT1, Melan A, vimentin, SALL4, GATA3, PAX8, and S-100 protein. Mutational analysis of exon 3 of the CTNNB1 gene by polymerase chain reaction (PCR)-amplified sequences and direct sequencing was performed. Results: Patients ages ranged from 22 to 65 years (mean 43 years). The clinical manifestation in all was a slowly enlarging, painless testicular mass.The maximum diameter of the tumor ranged from 1.5 cm to 3.0 cm (mean 2.1 cm). Sectioning usually disclosed a tan-gray to white mass with vague lobular cut-surface. Microscopically, the tumors were well circumscribed and non-encapsulated; the tumor cells were rearranged in multiple growth patterns from diffuse solid sheets to trabeculae and cords, ribbon and solid or hollow tubules setting in variable amount of acellular fibrous stroma. Two cases showed acellular collagenous stroma constituted >50% of the tumor confirming to the diagnosis of sclerosing SCT. One case demonstrated a prominent myxoid stromal change. The tumor cells typically had moderate amounts of pale to lightly eosinophilic cytoplasm, 2 tumors had variable cells with abundant lipid-rich cytoplasm, and 1 other tumor showed scattered aggregates of multinucleated tumor cells. The tumor cells were bland-appearing without any evidence of atypia, mitoses were noted in 2 tumors (both were 1/50 HPF), but necrosis was absent. Immunohistochemical staining results as follows: vimentin (diffuse, 7/7), CD10 (diffuse membrane, 7/7); diffuse β-catenin nuclear and cytoplasm staining in 5 of 7 cases, and all the 5 cases showed diffuse cyclin D1 nuclear staining, β-catenin membrane staining in 2 of 7 cases, CKpan (5/7, focal or diffuse), calretinin (focal, 5/6), inhibin (focal, 3/7), synaptophysin (focal, 2/6), CD56 (focal or diffuse, 4/5), WT1 (diffuse nuclear, 4/5), and S-100 protein (diffuse, 3/7), and chromogranin A, Melan A, PAX8, GATA3 and SALL4 all were negative. Molecular genetic studies of PCR and direct sequencing showed CTNNB1 mutations in 4 of 7 (4/7) cases, 4 of the four mutation-carrying cases showed diffuse β-catenin nuclear and cytoplasm immunoreactivity and diffuse cyclin D1 nuclear immunoreactivity in the tumor cells. Conclusions: SCT, NOS of the testis typically shows significant heterogeneities in both morphology and immunohistochemistry, thus causing differential diagnostic confusions. Molecular analyses showed mutations of exon 3 of CTNNB1 in more than half of these tumors, and nuclear accumulation of β-catenin and over expression of cyclin D1 can be useful for the differential diagnosis of SCT, NOS.