BRCA1 and breast cancer: In a case–control study of 965 BRCA1 and 280 BRCA2 pairs, breast feeding did not influence breast cancer risk in BRCA2 carriers, but BRCA1 carriers who breast fed for over 1 year were less likely to have had breast cancer than those who never breast fed (OR=0.55, 95% CI 0.38–0.80) (Jernstrom et al, 2004).