We assess whether genetic variation in CYP19A1 is associated with risk of BC in a case-control study group nested within the DCH cohort; and search for gene-gene interactions with CYP19A1 and PPARGC1A, and CYP19A1 and PPARG, and gene-alcohol and gene-NSAID interactions (interactions between PPARG and PPARGC1A were examined and published previously [30]). The gene discussed is CYP19A1; the disease is breast cancer.