CYP2C19*17 is a new variant allele which is associated with increased gene transcription and therefore higher enzyme activity [17]; which may lead to several clinical consequences including the lower susceptibility to breast cancer risk [35], higher risk of peptic ulcer disease [36], greater response to clopidogrel treatment and more risk of bleeding [37] in addition to a better treatment with tamoxifen [38]. This evidence concerns the gene CYP2C19 and breast carcinoma.