First description of a double heterozygosity for BRCA1 and BRCA2 pathogenic variants in a French metastatic breast cancer patient: A case report

Hereditary breast and ovarian cancer syndrome is an autosomal dominant disease caused primarily by germline mutations in the BRCA1 or BRCA2 gene. Rare cases of double heterozygosity for BRCA1 and BRCA2 mutations have been reported quite exceptionally in non-Ashkenazi individuals. We describe the case of a woman who developed a bilateral breast cancer, discovered concomitantly, at 46 years old. Biopsies confirmed the presence of two breast cancers with distinct histology. BRCA analysis was tested due to a positive family history of breast cancer, and two pathogenic monoallelic mutations were detected, one in the BRCA1 gene and one in the BRCA2 gene. There is no known Ashkenazi Jewish ancestry. We report the first description of a never described double heterozygosity for BRCA1 and BRCA2 pathogenic variants in a French metastatic breast cancer patient, with two distinct histology, and two distinct mutations.