CYP2C19*17 association with higher plasma 4-hydroxy tamoxifen in Pakistani (estrogen-positive) breast cancer patients

Breast cancer (BC) continues to be the most common cancer in the women worldwide. Since estrogen receptor (ER)-positive BC accounts for the majority of newly diagnosed cases, endocrine therapy is advised to utilize either tamoxifen (Tam) or aromatase inhibitors. The use of Tam as a monotherapy or in conjunction with an aromatase inhibitor following two or three years of endocrine therapy has long been recommended. When used adjuvantly, Tam medication reduces BC mortality and relapses, while it extends survival times in metastatic BC when used in conjunction with other treatments. Unfortunately, the efficiency of Tam varies considerably. This study was conducted to explore the influence of genetic polymorphisms in CYP2C19 gene on Tam's pharmacogenetics and pharmacokinetics in estrogen-positive BC patients. Data from healthy, unrelated individuals (n = 410; control group) and ER-positive BC patients (n = 430) receiving 20 mg of Tam per day were recruited. Steady-state plasma concentrations of Tam and its three metabolites were quantified using the high-performance liquid chromatography in the patients. The CYP2C19 polymorphisms were genotyped using an Amplification Refractory Mutation System-Polymerase Chain Reaction (ARMS-PCR) approach. More than 65% of healthy individuals were extensive metabolizers (*1/*1) for CYP2C19, whereas more than 70% of ER-positive BC patients were rapid and ultrarapid metabolizers (*1/17*, *17/17*). The polymorphism CYP2C19*17 is significantly associated with higher 4-hydroxytamoxifen (4-OH-Tam). Patients with the *17/*17 genotype exhibited 1- to 1.5-fold higher 4-OH-Tam, which was also high in patients with the *1/*2 and *2/*2 genotypes.