The present study, with at least 3 times the number of carriers, shows the protective effect on breast cancer between 20 and 50 years of age, of early full- term first pregnancy with odds ratios of 0.77 and 0.73 for BRCA1 and BRCA2 mutation carriers, respectively, and in prospective analysis, an even better odds ratio for both combined at 0.61. This evidence concerns the gene BRCA1 and breast cancer.