Women with breast cancer type 1 susceptibility gene (BRCA1) germline pathogenic variants are at high risk of triple-negative breast cancer (TNBC) and high-grade serous ovarian cancer (HGSOC).1BRCA1, like BRCA2 and several other genes, is required for homologous recombination repair of double-stranded DNA breaks.2 While most TNBCs and HGSOCs have gene expression profiles indicating homologous recombination deficiency (HRD),3,4,5 in many cases, no genetic alteration explains the HRD-positive status. This evidence concerns the gene BRCA1 and ovarian serous adenocarcinoma.