SMARCA4-deficient undifferentiated carcinoma of the ovary (small cell carcinoma, hypercalcemic type): clinicopathologic and immunohistochemical study of 3 cases.

Small cell carcinoma of the ovary, hypercalcemic type is a very rare aggressive neoplasm of unknown histogenesis, affecting mainly girls and young women. Recently, inactivating mutations in SMARCA4 (BRG1), a member of the switch/sucrose nonfermenting chromatin remodeling complex, has been identified as driver events in most cases. We herein describe 3 cases in 34, 34, and 37-year-old women. Symptoms were mainly abdominal pain and mass. One patient was normocalcemic, and the other 2 had no preoperative serum calcium values available. All patients received radical hysterectomy with salpingo-oophorectomy, lymphadenectomy, and variable multimodality therapy. Two developed abdominal recurrences/metastases and died of disease at 4 and 12 months. One patient was alive without disease 17 months after surgery and radiochemotherapy. Histologic examination showed undifferentiated neoplasms composed of diffuse sheets, nests and cords of noncohesive monomorphic small blue/basaloid cells (classic variant, 1 case), and large undifferentiated/rhabdoid cells with abundant cytoplasm (large cell/rhabdoid variant, 2 case) admixed with minor small cell areas. One case contained rare isolated goblet cells, but true glandular component was absent. All tumors expressed vimentin and variably pancytokeratin and WT1. Nuclear SMARCB1 was intact in all cases (1 case showed small foci with mosaic loss). All tumors showed complete loss of SMARCA4. In conclusion, SMARCA4 immunohistochemistry represents a highly valuable emerging tool in identifying small cell carcinoma of the ovary, hypercalcemic type in routine practice. Distinguishing this aggressive neoplasm from juvenile granulosa cell tumor and other undifferentiated ovarian cancers is mandatory in selecting appropriate chemotherapeutic regimens and would allow better characterization of this entity, for which targeted molecular therapy still remains to be established.