However, in BRCA1 mutation carriers a younger age at first IVF treatment seemed to be more strongly related with breast cancer risk than first IVF treatment at older ages (≤32 years HR: 1.91, 95% CI: 0.88–4.16, >32 years HR: 0.70, 95% CI: 0.28–1.76), but numbers were small. This evidence concerns the gene BRCA1 and breast cancer.