Prevalence of mutations in a panel of breast cancer susceptibility genes in BRCA1/2-negative patients with early-onset breast cancer.

Clinical testing for germ-line variation in multiple cancer susceptibility genes is available using massively parallel sequencing. Limited information is available for pretest genetic counseling regarding the spectrum of mutations and variants of uncertain significance in defined patient populations. We performed massively parallel sequencing using targeted capture of 22 cancer susceptibility genes in 278 BRCA1/2-negative patients with early-onset breast cancer (diagnosed at younger than 40 years of age). Thirty-one patients (11%) were found to have at least one deleterious or likely deleterious variant. Seven patients (2.5% overall) were found to have deleterious or likely deleterious variants in genes for which clinical guidelines exist for management, namely TP53 (4), CDKN2A (1), MSH2 (1), and MUTYH (double heterozygote). Twenty-four patients (8.6%) had deleterious or likely deleterious variants in a cancer susceptibility gene for which clinical guidelines are lacking, such as CHEK2 and ATM. Fifty-four patients (19%) had at least one variant of uncertain significance, and six patients were heterozygous for a variant in MUTYH. These data demonstrate that massively parallel sequencing identifies reportable variants in known cancer susceptibility genes in more than 30% of patients with early-onset breast cancer. However, only few patients (2.5%) have definitively actionable mutations given current clinical management guidelines.Genet Med 17 8, 630-638.