OBJECTIVETo study the clinicopathologic features of small cell carcinoma of ovary, hypercalcemic type (SCCOHT) and to evaluate the diagnostic significance of loss of SMARCA4 expression.

METHODSThe clinicopathologic characteristics of 5 cases of SCCOHT were reviewed. The expression of SMARCA4 protein was detected by immunohistochemistry in the cases of SCCOHT and 240 cases of other primary malignant tumors of ovary and peritoneum.

RESULTSThe mean and medium age of these patients was 30 years and 28 years, respectively. The presenting symptoms included abdominal pain, distention and a pelvic mass. Hypercalcemia was found in 3 patients. The maximum diameter of tumors ranged from 13.5 to 22.0 cm. Extraovarian spread was demonstrated in all of the patients on presentation. Histologically, the tumors were composed of closely packed small round cells with scanty cytoplasm, hyperchromatic nuclei and irregular chromatin clumps. The tumor cells grew in sheets, nests, cords or trabecular pattern. Follicle-like spaces were observed in 4 cases. Three of the tumors contained large cells with abundant eosinophilic cytoplasm. Spindle cell morphology was found in 1 case. There were 2 cases with myxoid or hyaline stroma. Four out of five of SCCOHT cases showed loss of SMARCA4 protein while only 6.3% (15/240) of the other primary malignant tumors of ovary and peritoneum , including undifferentiated carcinoma (1/5), high-grade serous carcinoma (4.6%, 5/109), endometrioid carcinoma (7.7%, 2/26), clear cell carcinoma (1/9), mucinous carcinoma (1/5), mixed carcinoma (4.9%, 3/61), carcinosarcoma (1/9) and high-grade serous carcinoma of peritoneum (1/9), were negative.

CONCLUSIONSSCCOHT is a rare malignant tumor and often misdiagnosed as other types of ovarian small cell tumor. Loss expression of SMARCA4 protein is characteristic and facilitates the diagnosis and differential diagnosis of SCCOHT.