BRCA1 and breast cancer: Overall, 5.6% of patients, including 7.6% (55 of 721) patients diagnosed before age 50 and 3.4% (22 of 649) patients diagnosed between ages 50 and 74, carried a pathogenic variant in BRCA1, BRCA2, PALB2, or TP53, the four most highly penetrant breast cancer genes.