Association between the MDR1 rs1045642 polymorphism and breast cancer risk: An updated meta‑analysis.

Multidrug resistance 1 (MDR1) is a transmembrane transporter on the cell membrane. As an ATP-dependent efflux pump, MDR1 is mainly responsible for the adsorption, distribution, metabolism, excretion and transportation of anticancer drugs to cancer cells. Mutations of the MDR1 gene may be associated with the incidence of cancer. In the past decade, associations found between the MDR1 rs1045642 polymorphism and breast cancer have been inconsistent and inconclusive. Therefore, the present study performed a meta-analysis including studies published up until August 16, 2023 to systematically evaluate the association between the MDR1 rs1045642 polymorphism and breast cancer risk. A total of 21 published case studies involving 6,815 patients with breast cancer and 9,227 healthy participants were included in the meta-analysis. Overall, the MDR1 rs1045642 polymorphism was not significantly associated with breast cancer-associated risk. However, in the subgroup analysis, the MDR1 rs1045642 polymorphism was found to be notably associated with a higher risk of breast cancer among Asian populations in recessive models [TT vs. CT + CC; odds ratio (OR)=1.393; 95% confidence interval (CI), 1.143-1.698; P=0.001; I<25%]. The MDR1 C3435T polymorphism was also associated with a notable decrease in the incidence of breast cancer in mixed ethnicity populations (TT and CT + CC; OR=0.578; 95% CI, 0.390-0.856; P=0.006; I<25%). In Caucasian populations, the MDR1 rs1045642 polymorphism was not associated with breast cancer risk. In conclusion, the present meta-analysis demonstrated that the MDR1 rs1045642 polymorphism may increase the risk of breast cancer in Asian populations, is associated with a reduced risk of breast cancer in mixed populations but has no notable effect in Caucasian populations.