Multiple Somatic Mutations of SMARCA4 in Small Cell Carcinoma of the Ovary, Hypercalcemic Type: A Case Report

Small-cell carcinoma of the ovary, the hypercalcemic type (SCCOHT) is a rare, aggressive tumor that primarily affects young females. It is a monogenic disorder caused by germline and/or somatic SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a, member 4 (SMARCA4) mutations. Here, we report a case of SCCOHT harboring multiple previously unreported somatic mutations in SMARCA4 (c.2866_2867delC>T; c.3543del). A 28-year-old breastfeeding Japanese female presented to a previous hospital with nausea and vomiting. She had no family history of relevant malignancies, including ovarian cancer. Based on an evaluation performed at another institution, she was referred to a gynecologist for suspected ovarian cancer. Imaging studies revealed a 16x15 cm heterogenous enhancing mass within the right ovary without lymph node or distant metastasis. She had mild ascites without peritoneal dissemination, but there was an elevation in the serum calcium level (15.1 mg/dL). The patient underwent cytoreductive surgery and was pathologically diagnosed with SCCOHT. Auxiliary immunohistochemical staining confirmed the loss of SMARCA4 protein expression. The patient was diagnosed with the International Federation of Gynecology and Obstetrics (FIGO) 2014 stage IA (pT1a pN0 M0). The serum calcium levels returned to normal post-surgery. Matched-pair analysis using tumor tissue and peripheral blood revealed multiple somatic mutations in SMARCA4 , but no deleterious germline mutations were present. Microsatellite instability was not significant, and the patients had a heterozygous mutation of uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1)*6 . She underwent six cycles of irinotecan hydrochloride plus cisplatin chemotherapy and achieved complete remission. The patient was finally examined and evaluated 45 months postoperatively; there was no evidence of the disease. Overall, the genetic findings will not aid in the SCCOHT diagnosis and relevant genetic counseling; however, they may have implications for the treatment of this disease in the future.