Impact of CYP3A4 and CYP3A5 single nucleotide polymorphisms on anastrozole-associated adverse events among Malaysian breast cancer patients

The catalytic activity of the cytochrome P450A (CYP3A4) enzyme is reportedly affected by the presence of single nucleotide polymorphisms (SNPs), leading to inter-individual variability in drug efficacy and adverse reactions. CYP3A4 polymorphisms can serve as potential biomarkers for predicting the efficacy of many drugs, including those used in breast cancer treatment. This study was conducted on 94 hormone receptor-positive postmenopausal breast cancer patients who received 1 mg of anastrozole per day. Anastrozole-associated adverse events (AAAEs), such as musculoskeletal adverse events (MSAEs), hot flashes, mood disturbance and vaginal dryness/dyspareunia, were assessed according to the Common Terminology Criteria for Adverse Events (CTCAE). The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was performed to determine the allelic frequency of CYP3A4*4, CYP3A4*18A, CYP3A4*18B, CYP3A4*22 and CYP3A5*3. The frequencies of CYP3A4*18A T>C (rs28371759), CYP3A4*18B G>A (rs2242480) and CYP3A5*3 were 0.03, 0.48 and 0.64, respectively. However, no CYP3A4*4 A>G (rs55951658) or CYP3A4*22 C>T (rs35599367) alleles were detected. No significant association was observed between the alleles and the development of AAAEs. We have demonstrated for the first time that CYP3A4*18B G>A is highly prevalent among Malaysian breast cancer patients. The clinical relevance of CYP3A4*18B is currently under investigation by our group.