title: Impact of variable CYP genotypes on breast cancer relapse in patients undergoing adjuvant tamoxifen therapy.
abstract: BACKGROUND
  Tamoxifen is frequently used for the treatment of hormone receptor positive breast cancer (BC). Mainly CYP2D6 is responsible for the transformation to therapeutically active metabolites, but CYP2C19, CYP2C9 and CYP2B6 also are involved. We investigated the impact of polymorphisms within the genes encoding these CYP enzymes on the relapse-free time (RFT) in patients with BC.
  
  
  METHODS
  Ninety-nine patients with hormone receptor positive BC, who had undergone adjuvant tamoxifen therapy, were genotyped for seventeen common variants within the genes encoding CYP2D6, CYP2C9, CYP2C19 and CYP2B6 using TaqMan and PCR-RFLP technology. Kaplan-Meier and Cox regression analyses were performed to elucidate the impact of genetic variants on RFT. Furthermore, CYP2D6 metabolic activity was determined in a subset of 50 patients by assessing dextromethorphan/dextrorphan urinary excretion ratios. CYP2D6 activity was compared to the CYP2D6 allelic combinations to evaluate the predictive value of the CYP2D6 genotyping results on phenotype.
  
  
  RESULTS
  Although a trend toward longer RFTs in carriers of CYP2D6 allele combinations encoding for extensive and ultrafast metabolizer phenotypes was observed, none of the investigated genetic variants had a statistically significant impact on RFT. The combined analysis of five major CYP2D6 variants was useful for the discrimination between poor and non-poor metabolizers.
  
  
  CONCLUSIONS
  Comprehensive CYP2D6 genotyping has a good predictive value for CYP2D6 activity. Common variants in CYP2C9, CYP2C19, CYP2D6, and CYP2B6 did not have a significant impact on the RFT in this cohort of patients with BC.
authors.affiliation: Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Jessica
authors.initials: J
authors.lastname: Mwinyi
authors.forename: Kerstin
authors.initials: K
authors.lastname: Vokinger
authors.forename: Alexander
authors.initials: A
authors.lastname: Jetter
authors.forename: Urs
authors.initials: U
authors.lastname: Breitenstein
authors.forename: Christian
authors.initials: C
authors.lastname: Hiller
authors.forename: Gerd A
authors.initials: GA
authors.lastname: Kullak-Ublick
authors.forename: Andreas
authors.initials: A
authors.lastname: Trojan
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics*; D017024:Chemotherapy, Adjuvant; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005838:Genotype; D006801:Humans; D007527:Isoenzymes; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D011110:Polymorphism, Genetic; D013629:Tamoxifen / Q000493:pharmacokinetics / Q000627:therapeutic use
chemical_list: D007527:Isoenzymes; D013629:Tamoxifen; D019389:Cytochrome P-450 CYP2D6