CYP2D6 genotyping in breast cancer patients by liquid chromatography-electrospray ionization mass spectrometry

The application of cytochrome P450 2D6 (CYP2D6) genotyping to allow a personalized treatment approach for breast cancer patients undergoing endocrine therapy has been repeatedly discussed. However, the actual clinical relevance of the CYP2D6 genotype in the endocrine treatment of breast cancer still remains to be elucidated. A major prerequisite for the successful and valid evaluation of the CYP2D6 genotype with regard to its pharmacokinetic and clinical relevance is the availability of a comprehensive, accurate and cost-effective CYP2D6 genotyping strategy. Herein we present a CYP2D6 genotyping assay employing polymerase chain reaction (PCR)-ion pair reversed-phase high-performance liquid chromatography-electrospray ionization time-of-flight mass spectrometry (ICEMS). The genotyping strategy involves the simultaneous amplification of nine variable regions within the CYP2D6 gene by a two-step PCR protocol and the direct analysis of the generated PCR amplicons by ICEMS. The nucleotide composition profiles generated by ICEMS enable the differentiation of 37 of the 80 reported CYP2D6 alleles. The assay was applied to type the CYP2D6 gene in 199 Austrian individuals including 106 breast cancer patients undergoing tamoxifen treatment. The developed method turned out to be a highly applicable, robust and cost-effective approach, enabling an economical CYP2D6 testing for large patient cohorts.