Breast Cancer has been associated with polymorphisms in genes candidate to be disease modifiers, such as CYP19 (Family 19 of the Cytochrome P450), GSTP1 (Glutathione S-Transferase Protein), TP53 (Tumor Protein 53), P21 (Protein 21) [19], MTHFR (Methylenetetrahydrofolate Reductase) and TYMS (Thymidylate Synthase) [20] and, which are involved in events such as synthesis, methylation and DNA damage repair, and cellular activation in carcinogen metabolism and the metabolism of anticancer drugs. This evidence concerns the gene CYP19A1 and breast cancer.