BRCA1 and breast cancer: Categorizing age at first breast cancer diagnosis for BRCA1 heterozygotes resulted in HRs per SD of the ER-negative PRS313 of 1.22, 95% CI (1.14–1.31); 0.99, 95% CI (0.90–1.09);, and 1.03, 95% CI (0.86–1.24) for ages <40 years, 40–50 years, and ≥50 year respectively.