The odds ratios for breast cancer diagnosed at age 40 or below were 28.8 for BRCA1 (95% CI 18.6–44.5); 3.8 for CHEK2 (95% CI 2.5–5.5); and 3.6 for PALB2 (95% CI 1.6–7.5), and all were statistically significant. This evidence concerns the gene BRCA1 and breast cancer.