Implementation of next-generation sequencing for molecular diagnosis of hereditary breast and ovarian cancer highlights its genetic heterogeneity

Molecular diagnosis of hereditary breast and ovarian cancer (HBOC) by standard methodologies has been limited to the BRCA1 and BRCA2 genes. With the recent development of new sequencing methodologies, the speed and efficiency of DNA testing have dramatically improved. The aim of this work was to validate the use of next-generation sequencing (NGS) for the detection of BRCA1/BRCA2 point mutations in a diagnostic setting and to study the role of other genes associated with HBOC in Portuguese families. A cohort of 94 high-risk families was included in the study, and they were initially screened for the two common founder mutations with variant-specific methods. Fourteen index patients were shown to carry the Portuguese founder mutation BRCA2 c.156_157insAlu, and the remaining 80 were analyzed in parallel by Sanger sequencing for the BRCA1/BRCA2 genes and by NGS for a panel of 17 genes that have been described as involved in predisposition to breast and/or ovarian cancer. A total of 506 variants in the BRCA1/BRCA2 genes were detected by both methodologies, with a 100 % concordance between them. This strategy allowed the detection of a total of 39 deleterious mutations in the 94 index patients, namely 10 in BRCA1 (25.6 %), 21 in BRCA2 (53.8 %), four in PALB2 (10.3 %), two in ATM (5.1 %), one in CHEK2 (2.6 %), and one in TP53 (2.6 %), with 20.5 % of the deleterious mutations being found in genes other than BRCA1/BRCA2. These results demonstrate the efficiency of NGS for the detection of BRCA1/BRCA2 point mutations and highlight the genetic heterogeneity of HBOC.