NBN and breast cancer: The monogenic BC variant distribution among counseled participants was as follows: 54.1% BRCA1, 23% BRCA2, 14.7% CHEK2, 5.5% ATM, 1.8% NBN, and 0.9% NF1. Risk-conferring variants were pathogenic in 95% of cases and likely pathogenic in 5% of cases (Table 1).