Concurrent germline BRCA1, BRCA2, and CHEK2 pathogenic variants in hereditary breast cancer: a case series.

BACKGROUND: Concurrent germline (g) pathogenic variants related to hereditary breast cancer represent a rare occurrence. While double heterozygosity in gBRCA1 and gBRCA2 has been reported in the past, herein we describe the first case of three known concurrent pathogenic variants identified in a family with a strong history of breast cancer. Case presentation The proband is a 55-year-old female diagnosed with synchronous bilateral breast cancers. She underwent a multi-gene panel testing indicating the presence of 3 concurrent heterozygous germline deleterious variants in BRCA1 (c.181T > G), BRCA2 (c.4398_4402delACATT), and CHEK2 (1100delC). The patient's two daughters (34 and 29 years-old) were found to be transheterozygous for inherited pathogenic variants in BRCA1 (c.181T > G) and CHEK2 (1100delC) genes.

CONCLUSION: The cancer risk and phenotypic manifestations associated with transheterozygous or multiple concurrent deleterious germline variants in hereditary breast cancer requires further investigation. A personalized approach to counseling, screening, and risk reduction should be undertaken for these individuals.