title: CYP2D6 gene variants: association with breast cancer specific survival in a cohort of breast cancer patients from the United Kingdom treated with adjuvant tamoxifen.
abstract: BACKGROUND
  Tamoxifen is one of the most effective adjuvant breast cancer therapies available. Its metabolism involves the phase I enzyme, cytochrome P4502D6 (CYP2D6), encoded by the highly polymorphic CYP2D6 gene. CYP2D6 variants resulting in poor metabolism of tamoxifen are hypothesised to reduce its efficacy. An FDA-approved pre-treatment CYP2D6 gene testing assay is available. However, evidence from published studies evaluating CYP2D6 variants as predictive factors of tamoxifen efficacy and clinical outcome are conflicting, querying the clinical utility of CYP2D6 testing. We investigated the association of CYP2D6 variants with breast cancer specific survival (BCSS) in breast cancer patients receiving tamoxifen.
  
  
  METHODS
  This was a population based case-cohort study. We genotyped known functional variants (n = 7; minor allele frequency (MAF) > 0.01) and single nucleotide polymorphisms (SNPs) (n = 5; MAF > 0.05) tagging all known common variants (tagSNPs), in CYP2D6 in 6640 DNA samples from patients with invasive breast cancer from SEARCH (Studies of Epidemiology and Risk factors in Cancer Heredity); 3155 cases had received tamoxifen therapy. There were 312 deaths from breast cancer, in the tamoxifen treated patients, with over 18000 years of cumulative follow-up. The association between genotype and BCSS was evaluated using Cox proportional hazards regression analysis.
  
  
  RESULTS
  In tamoxifen treated patients, there was weak evidence that the poor-metaboliser variant, CYP2D6*6 (MAF = 0.01), was associated with decreased BCSS (P = 0.02; HR = 1.95; 95% CI = 1.12-3.40). No other variants, including CYP2D6*4 (MAF = 0.20), previously reported to be associated with poorer clinical outcomes, were associated with differences in BCSS, in either the tamoxifen or non-tamoxifen groups.
  
  
  CONCLUSIONS
  CYP2D6*6 may affect BCSS in tamoxifen-treated patients. However, the absence of an association with survival in more frequent variants, including CYP2D6*4, questions the validity of the reported association between CYP2D6 genotype and treatment response in breast cancer. Until larger, prospective studies confirming any associations are available, routine CYP2D6 genetic testing should not be used in the clinical setting.
authors: Department of Oncology, Strangeways Research Laboratory, University of Cambridge, 2 Worts Causeway, Cambridge, CB1 8RN, UK. ja344@medschl.cam.ac.uk
authors: Jean E
authors: JE
authors: Abraham
authors: Mel J
authors: MJ
authors: Maranian
authors: Kristy E
authors: KE
authors: Driver
authors: Radka
authors: R
authors: Platte
authors: Bolot
authors: B
authors: Kalmyrzaev
authors: Caroline
authors: C
authors: Baynes
authors: Craig
authors: C
authors: Luccarini
authors: Mitul
authors: M
authors: Shah
authors: Susan
authors: S
authors: Ingle
authors: David
authors: D
authors: Greenberg
authors: Helena M
authors: HM
authors: Earl
authors: Alison M
authors: AM
authors: Dunning
authors: Paul D P
authors: PD
authors: Pharoah
authors: Carlos
authors: C
authors: Caldas
mesh_terms: D000328:Adult; D000368:Aged; D018931:Antineoplastic Agents, Hormonal / Q000378:metabolism / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000473:pathology; D017024:Chemotherapy, Adjuvant / Q000706:statistics & numerical data; D015331:Cohort Studies; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005787:Gene Frequency; D005838:Genotype; D006801:Humans; D008875:Middle Aged; D020641:Polymorphism, Single Nucleotide; D016016:Proportional Hazards Models; D016019:Survival Analysis; D013629:Tamoxifen / Q000378:metabolism / Q000627:therapeutic use*; D016896:Treatment Outcome; D006113:United Kingdom; D055815:Young Adult
chemical_list: D018931:Antineoplastic Agents, Hormonal; D013629:Tamoxifen; D019389:Cytochrome P-450 CYP2D6