Rs12248560

rs12248560(T) defines the CYP2C19*17 allele, an ultra fast metabolizer phenotype of the CYP2C19 gene.

CYP2C19*17 is likely to lead to less effective drug treatment by, for example, proton pump inhibitors (such as omeprazole) and antidepressants.

On the other hand, cancer patients who are CYP2C19*17 carriers are more likely to benefit from tamoxifen treatment, presumably because they break it down more rapidly into the antiestrogenic metabolites endoxifen and 4-hydroxytamoxifen.

A study of 1,000+ breast cancer patients showed a 0.77x decreased risk of breast cancer for carriers of a CYP2C19*17 allele (CI: 0.65-0.93, p = 0.005). Analysis of a subgroup of such carriers who were using hormone therapy for ten years or longer showed an even stronger effect (odds ratio 0.57, CI: 0.39-0.83, p = 0.003). The theory is that ultra fast metabolism of estrogen leads to lower estrogen levels and lower breast cancer risk.

Clopidogrel Efficacy