Comprehensive Functional Characterization and Clinical Interpretation of 20 Splice-Site Variants of the RAD51C Gene.

Hereditary breast and/or ovarian cancer is a highly heterogeneous disease with more than 10 known disease-associated genes. In the framework of the BRIDGES project (Breast Cancer Risk after Diagnostic Gene Sequencing), the RAD51C gene has been sequenced in 60,466 breast cancer patients and 53,461 controls. We aimed at functionally characterizing all the identified genetic variants that are predicted to disrupt the splicing process. Forty RAD51C variants of the intron-exon boundaries were bioinformatically analyzed, 20 of which were selected for splicing functional assays. To test them, a splicing reporter minigene with exons 2 to 8 was designed and constructed. This minigene generated a full-length transcript of the expected size (1062 nucleotides), sequence, and structure (Vector exon V1- RAD51C exons_2-8- Vector exon V2). The 20 candidate variants were genetically engineered into the wild type minigene and functionally assayed in MCF-7 cells. Nineteen variants (95%) impaired splicing, while 18 of them produced severe splicing anomalies. At least 35 transcripts were generated by the mutant minigenes: 16 protein-truncating, 6 in-frame, and 13 minor uncharacterized isoforms. According to ACMG/AMP-based standards, 15 variants could be classified as pathogenic or likely pathogenic variants: c.404G > A, c.405-6T > A, c.571 + 4A > G, c.571 + 5G > A, c.572-1G > T, c.705G > T, c.706-2A > C, c.706-2A > G, c.837 + 2T > C, c.905-3C > G, c.905-2A > C, c.905-2_905-1del, c.965 + 5G > A, c.1026 + 5_1026 + 7del, and c.1026 + 5G > T.

Peritoneal washing is an adequate source for somatic BRCA1/2 mutation testing in ovarian malignancies.

Genetic screening for BRCA mutations should be offered to all women diagnosed with epithelial ovarian, fallopian tube, and/or peritoneal cancers given the implications for treatment options and cancer risk assessments. Yet, while germline breast cancer susceptibility gene 1 (BRCA1) and breast cancer susceptibility gene 2 (BRCA2) testing is commonly performed, BRCA1/2 somatic mutations testing is rather challenging since the poor quality of DNA extracted from formalin fixed paraffin embedded (FFPE) samples can significantly impair this process. Peritoneal lavage is routinely performed in surgeries of suspected ovarian malignancies. We have analyzed fresh tumor, peritoneal lavage and blood samples from ten patients and we have found an excellent agreement (88%) between fresh tumor and peritoneal lavage for BRCA mutation testing. Importantly, 112 of the 114 genomic alterations detected in fresh tumor samples were also found in peritoneal lavage fluids. Our data suggest that peritoneal washings can indeed streamline BRCA genes mutation testing procedures.