CYP2C19 and breast cancer: In contrast, a decreased breast cancer risk for carriers of the CYP2C19*17 allele was observed in German women (Justenhoven et al., 2009), and a meta-analysis has found that CYP2C19*2 and CYP2C19*17 genotypes are associated with increased survival of breast cancer patients treated with tamoxifen (Bai et al., 2014).