Characterization of rare histological subtypes of ovarian cancer based on molecular profiling

OBJECTIVE: Pan‐cancer analysis across The Cancer Genome Atlas has revealed the molecular profiles of major types of carcinomas. High‐grade serous carcinomas (HGSCs) have been characterized; however, in ovarian cancer, the profile of carcinoma with minor histopathological changes remains unclear. This study aimed to perform the molecular profiling of rare malignant ovarian tumors, including non‐epithelial tumors (NETs; germ cell tumors and sex cord tumors) and clear cell carcinoma (CCC), to determine how they differ from the major HGSCs. METHODS: Sixty‐nine malignant ovarian tumors surgically resected at the Shizuoka Cancer Center between January 2014 and March 2019 were classified based on their histopathological types. The germline and somatic mutations in these carcinomas, including NETs, were determined using next‐generation sequencing. Gene expression analysis was performed to investigate the major pathways of drug resistance, which is a characteristic of CCC. RESULTS: NETs harbored copy‐neutral loss of heterozygosity, accompanied by a high homologous recombination deficiency score; germline mutations of PALB2 and BARD1 were identified in two patients with NET. In chemoresistant CCC, the epithelial‐mesenchymal transition pathway was activated regardless of ABC transporter expression. CONCLUSION: This study revealed some genomic characteristics of rare malignant ovarian tumors, including NETs and CCC.