Gene Summary

Gene:CYP2D6; cytochrome P450, family 2, subfamily D, polypeptide 6
Aliases: CPD6, CYP2D, CYP2DL1, CYPIID6, P450C2D, P450DB1, CYP2D7AP, CYP2D7BP, CYP2D7P2, CYP2D8P2, P450-DB1
Summary:This gene encodes a member of the cytochrome P450 superfamily of enzymes. The cytochrome P450 proteins are monooxygenases which catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids and other lipids. This protein localizes to the endoplasmic reticulum and is known to metabolize as many as 25% of commonly prescribed drugs. Its substrates include antidepressants, antipsychotics, analgesics and antitussives, beta adrenergic blocking agents, antiarrythmics and antiemetics. The gene is highly polymorphic in the human population; certain alleles result in the poor metabolizer phenotype, characterized by a decreased ability to metabolize the enzyme's substrates. Some individuals with the poor metabolizer phenotype have no functional protein since they carry 2 null alleles whereas in other individuals the gene is absent. This gene can vary in copy number and individuals with the ultrarapid metabolizer phenotype can have 3 or more active copies of the gene. Alternatively spliced transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Jul 2014]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:cytochrome P450 2D6
Source:NCBIAccessed: 16 March, 2015


What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1990-2015)
Graph generated 16 March 2015 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Chromosome 22
  • Cervical Cancer
  • Glutathione Transferase
  • Breast Cancer
  • United States Food and Drug Administration
  • Regression Analysis
  • Venous Thromboembolism
  • Genotype
  • Single-Stranded Conformational Polymorphism
  • Genetic Predisposition
  • Cytochrome P-450 Enzyme System
  • Structure-Activity Relationship
  • Molecular Sequence Data
  • Triglycerides
  • Ukraine
  • Young Adult
  • CYP2D6
  • Spain
  • Alleles
  • Vomiting
  • Skin Cancer
  • Bladder Cancer
  • Ribonuclease P
  • Women's Health
  • Smoking
  • Uterine Cancer
  • Restriction Fragment Length Polymorphism
  • Triazoles
  • Vulvar Cancer
  • Mutation
  • Tumor Markers
  • Sequence Deletion
  • Thyroid Cancer
  • Polymorphism
  • Reproducibility of Results
  • Xenobiotics
  • Antineoplastic Agents, Hormonal
  • Proportional Hazards Models
  • Substrate Specificity
Tag cloud generated 16 March, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (3)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: CYP2D6 (cancer-related)

Maximov PY, McDaniel RE, Fernandes DJ, et al.
Pharmacological relevance of endoxifen in a laboratory simulation of breast cancer in postmenopausal patients.
J Natl Cancer Inst. 2014; 106(10) [PubMed] Article available free on PMC after 01/10/2015 Related Publications
BACKGROUND: Tamoxifen is metabolically activated via a CYP2D6 enzyme system to the more potent hydroxylated derivatives 4-hydroxytamoxifen and endoxifen. This study addresses the pharmacological importance of endoxifen by simulating clinical scenarios in vitro.
METHODS: Clinical levels of tamoxifen metabolites in postmenopausal breast cancer patients previously genotyped for CYP2D6 were used in vitro along with clinical estrogen levels (estrone and estradiol) in postmenopausal patients determined in previous studies. The biological effects on cell growth were evaluated in a panel of estrogen receptor-positive breast cancer cell lines via cell proliferation assays and real-time polymerase chain reaction (PCR). Data were analyzed with one- and two-way analysis of variance and Student's t test. All statistical tests were two-sided.
RESULTS: Postmenopausal levels of estrogen-induced proliferation of all test breast cancer cell lines (mean fold induction ± SD vs vehicle control: MCF-7 = 11 ± 1.74, P < .001; T47D = 7.52 ± 0.72, P < .001; BT474 = 1.75 ± 0.23, P < .001; ZR-75-1 = 5.5 ± 1.95, P = .001. Tamoxifen and primary metabolites completely inhibited cell growth regardless of the CYP2D6 genotype in all cell lines (mean fold induction ± SD vs vehicle control: MCF-7 = 1.57 ± 0.38, P = .54; T47D = 1.17 ± 0.23, P = .79; BT474 = 0.96 ± 0.2, P = .98; ZR-75-1 = 0.86 ± 0.67, P = .99). Interestingly, tamoxifen and its primary metabolites were not able to fully inhibit the estrogen-stimulated expression of estrogen-responsive genes in MCF-7 cells (P < .05 for all genes), but the addition of endoxifen was able to produce additional antiestrogenic effect on these genes.
CONCLUSIONS: The results indicate that tamoxifen and other metabolites, excluding endoxifen, completely inhibit estrogen-stimulated growth in all cell lines, but additional antiestrogenic action from endoxifen is necessary for complete blockade of estrogen-stimulated genes. Endoxifen is of supportive importance for the therapeutic effect of tamoxifen in a postmenopausal setting.

Mwinyi J, Vokinger K, Jetter A, et al.
Impact of variable CYP genotypes on breast cancer relapse in patients undergoing adjuvant tamoxifen therapy.
Cancer Chemother Pharmacol. 2014; 73(6):1181-8 [PubMed] Related Publications
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.

Khlifi R, Chakroun A, Hamza-Chaffai A, Rebai A
Association of CYP1A1 and CYP2D6 gene polymorphisms with head and neck cancer in Tunisian patients.
Mol Biol Rep. 2014; 41(4):2591-600 [PubMed] Related Publications
The purpose of this study was to investigate the relationship between head and neck cancer (HNC) and environmental agents and polymorphisms in CYP1A1, CYP2D6, NAT1 and NAT2 metabolic enzymes genes. To the best of our knowledge, this is the first report on polymorphisms in CYP1A1 6310C>T, CYP2D6 Arg365His, NAT1 52936A>T and NAT2 Arg268Lys (NAT2*12A) genes and susceptibility to HNC in Tunisian population. We study the prevalence of these polymorphisms in 169 patients with HNC and 261 control subjects using polymerase chain reaction based methods in a Tunisian population. We detected an association between HNC and CYP1A1 6310C>T (TT) and CYP2D6 Arg365His (His/His) variant carriers (OR 1.75, P = 0.008 and OR 1.66, P = 0.016, respectively). No association was found between the polymorphisms genotypes of NAT1 52936T>A and NAT2 Arg268Lys and risk of HNC. An association between HNC and CYP1A1 (TT) genotype was found among patients with smoking (P = 0.011) and drinking habit (P = 0.009). The combinations of NAT1 (AT or AA) and NAT2 (AA) at-risk genotypes increased HNC risk (OR 4.23, P = 0.005 and OR 3.60, P = 0.048, respectively). However, the combinations of CYP1A1 (AA) and CYP2D6 (CC) genotypes decreased risk of HNC (OR 0.20; P = 0.006). Genetic polymorphisms in CYP1A1 and CYP2D6 may significantly associate with HNC in the Tunisian population. The results of this study suggest a possible gene-environment interaction for certain carcinogen metabolizing enzymes, but larger studies that fully evaluate the interaction are needed.

Cronin-Fenton DP, Damkier P, Lash TL
Metabolism and transport of tamoxifen in relation to its effectiveness: new perspectives on an ongoing controversy.
Future Oncol. 2014; 10(1):107-22 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
Tamoxifen reduces the rate of breast cancer recurrence by approximately a half. Tamoxifen is metabolized to more active metabolites by enzymes encoded by polymorphic genes, including cytochrome P450 2D6 (CYP2D6). Tamoxifen is a substrate for ATP-binding cassette transporter proteins. We review tamoxifen's clinical pharmacology and use meta-analyses to evaluate the clinical epidemiology studies conducted to date on the association between CYP2D6 inhibition and tamoxifen effectiveness. Our findings indicate that the effect of both drug-induced and/or gene-induced inhibition of CYP2D6 activity is likely to be null or small, or at most moderate in subjects carrying two reduced function alleles. Future research should examine the effect of polymorphisms in genes encoding enzymes in tamoxifen's complete metabolic pathway, should comprehensively evaluate other biomarkers that affect tamoxifen effectiveness, such as the transport enzymes, and focus on subgroups of patients, such as premenopausal breast cancer patients, for whom tamoxifen is the only guideline endocrine therapy.

Dieudonné AS, Lambrechts D, Smeets D, et al.
The rs1800716 variant in CYP2D6 is associated with an increased double endometrial thickness in postmenopausal women on tamoxifen.
Ann Oncol. 2014; 25(1):90-5 [PubMed] Related Publications
BACKGROUND: Tamoxifen remains important in the treatment and prevention of estrogen receptor-positive breast cancer. In postmenopausal women, it can lead to endometrial changes such as cystic appearances, hyperplasia, polyps and endometrial cancer. Tamoxifen is metabolized by cytochrome P450 (CYP450) enzymes to the more active metabolite endoxifen. Several genetic variants in the CYP450 enzymes reduce tamoxifen metabolism, leading to reduced endoxifen levels. We hypothesize that carriers of these variants, which are established poor metabolizers of tamoxifen, do not have the typical tamoxifen-induced increase in endometrial thickness. We test the association between genetic variability in CYP450 enzymes and the increase in double endometrial thickness (DET) as measured through transvaginal ultrasound (TVU).
PATIENTS AND METHODS: We carried out a retrospective study on postmenopausal tamoxifen users for which germline DNA was available and at least one DET measurement was made between January 2000 and October 2011. Genotyping of 33 single nucleotide polymorphisms in CYP450 genes involved in tamoxifen metabolism was carried out using Sequenom MassARRAY. The association between these variants and TVU outcome (DET ≥5 mm) was assessed by proportional hazards regression.
RESULTS: Data were available for 184 women: 47 with a DET of <5 mm on all ultrasounds and 137 with a DET of ≥5 mm on at least one ultrasound. The rs1800716 variant in CYP2D6 showed a statistically significant association with DET. In particular, mutant carriers of rs1800716 had an increased chance of having a DET of ≥5 mm (P = 0.0022, false discovery rate 0.0179). None of the other variants were associated with DET.
CONCLUSION: Although mutant carriers of rs1800716 are characterized by reduced CYP2D6 enzyme activity and by low levels of endoxifen, we observed that mutant alleles of rs1800716 were associated with an increased chance of having a DET of ≥5 mm in postmenopausal women on tamoxifen. We conclude that the increase in endometrial thickness seen under tamoxifen cannot be used as a marker for favorable genotypes.

Dezentjé VO, Gelderblom H, Van Schaik RH, et al.
CYP2D6 genotype in relation to hot flashes as tamoxifen side effect in a Dutch cohort of the tamoxifen exemestane adjuvant multinational (TEAM) trial.
Breast Cancer Res Treat. 2014; 143(1):171-9 [PubMed] Related Publications
In tamoxifen-treated breast cancer patients the occurrence of hot flashes may be associated with effective estrogen receptor antagonism dependent on genetic variations of metabolic enzymes and the estrogen receptor. Early breast cancer patients who were randomized to receive tamoxifen, followed by exemestane within the tamoxifen exemestane adjuvant multinational trial were genotyped for five CYP2D6 alleles. CYP2D6 genotypes and phenotypes were related to the occurrence of hot flashes as adverse event during the first year of tamoxifen use (primary aim) and the time to the occurrence of hot flashes as AE during the complete time on tamoxifen (secondary aim). In addition, exploratory analyses on 22 genetic variants of other metabolic enzymes and two common polymorphisms in the estrogen receptor-1 were performed. No association was found between the CYP2D6 genotype/phenotype or any other genetic variant and hot flashes during the first year. Only higher age was related to a lower incidence of hot flashes in the first year (adjusted odds ratio 0.94, 95 % CI 0.92-0.96; p < 0.001). The ESR1 PvuII XbaI CG haplotype was associated with the time to the occurrence of hot flashes during the complete time on tamoxifen (CG/CG vs. CG/other + other/other: adjusted hazard ratio 0.49, 95 % CI 0.25-0.97; p = 0.04). In conclusion, the CYP2D6 genotypes and phenotypes were not associated with the occurrence of hot flashes. Common polymorphisms in the estrogen receptor-1 might predict hot flashes as common tamoxifen side effect, although this finding needs replication.

Smith EC
Understanding CYP2D6 and its role in tamoxifen metabolism.
Oncol Nurs Forum. 2013; 40(6):547-8 [PubMed] Related Publications
The gene CYP2D6 has an extremely important role in drug metabolism. "Cytochrome P450, family 2, subfamily D, polypeptide 6" is the official name of CYP2D6. The gene is located at position 13.1 on the long (q) arm of chromosome 21 and encodes a member of the cytochrome P450 superfamily of enzymes. The cytochrome P450 proteins are monooxygenases that are heavily involved in drug metabolism (Genetics Home Reference, 2013), and many drugs are activated into their biologically active compounds. Because of numerous polymorphisms, the gene also has significant person-to-person variability. To date, more than 80 distinct CYP2D6 alleles and specific types and frequencies have been associated with different ethnic groups. CYP2D6*4 is the most common variant allele in Caucasians and, in that population, has a frequency of about 25%. On the other hand, CYP2D6*10 is common in the Asian population (Stearns & Rae, 2008).

Khlifi R, Messaoud O, Rebai A, Hamza-Chaffai A
Polymorphisms in the human cytochrome P450 and arylamine N-acetyltransferase: susceptibility to head and neck cancers.
Biomed Res Int. 2013; 2013:582768 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
The occurrence of head and neck cancer (HNC) is associated with smoking and alcohol drinking. Tobacco smoking exposes smokers to a series of carcinogenic chemicals. Cytochrome P450 enzymes (CYP450s), such as CYP1A1, CYP1B1, and CYP2D6, usually metabolize carcinogens to their inactive derivatives, but they occasionally convert the chemicals to more potent carcinogens. In addition, via CYP450 (CYP2E1) oxidase, alcohol is metabolized to acetaldehyde, a highly toxic compound, which plays an important role in carcinogenesis. Furthermore, two N-acetyltransferase isozymes (NATs), NAT1 and NAT2, are polymorphic and catalyze both N-acetylation and O-acetylation of aromatic and heterocyclic amine carcinogens. Genetic polymorphisms are associated with a number of enzymes involved in the metabolism of carcinogens important in the induction of HNC. It has been suggested that such polymorphisms may be linked to cancer susceptibility. In this paper, we select four cytochrome P450 enzymes (CYP1A1, CYP1BA1, CYP2D6, and CYP2E1), and two N-acetyltransferase isozymes (NAT1 and NAT2) in order to summarize and analyze findings from the literature related to HNC risk by focusing on (i) the interaction between these genes and the environment, (ii) the impact of genetic defect on protein activity and/or expression, and (iii) the eventual involvement of race in such associations.

Ruan XL, Li S, Zeng XT, et al.
No association between cytochrome P450 2D6 gene polymorphism and risk of acute leukemia: evidence based on a meta-analysis.
Chin Med J (Engl). 2013; 126(19):3750-3 [PubMed] Related Publications
BACKGROUND: Many studies indicated the human cytochrome P450 2D6 (CYP2D6) gene polymorphism was associated with acute leukemia (AL) susceptibility, however, the results were inconsistent. So we performed this meta-analysis to evaluate the relationship between CYP2D6*3 or CYP2D6*4 polymorphism and AL susceptibility.
METHODS: We searched PubMed database up to February 20, 2013, and finally yielded 9 case-control studies including 1343 cases and 1843 controls which tested the association between CYP2D6*3 or *4 polymorphism and AL. After data extraction, we conducted a meta-analysis using the Comprehensive Meta Analysis software.
RESULTS: Overall, no significant association between CYP2D6*3 or *4 polymorphism and AL risk was found in this metaanalysis (+ vs. -: OR = 1.13, 95% CI = 0.79-1.63; +/+ vs. -/-: OR = 1.73, 95% CI = 0.99-3.02; -/+ vs. -/-: OR = 1.03, 95% CI = 0.68-1.56; (-/+ and +/+) vs. -/-: OR = 1.08, 95% CI = 0.72-1.63; +/+ vs. (-/+ and -/-): OR = 1.76, 95% CI = 0.98-3.17). Similar results were also been found in stratified subgroup analysis. There was no publication bias.
CONCLUSION: CYP2D6*3 or *4 polymorphism might not be associated with AL susceptibility. However, the results need to be further confirmed by well-designed and high quality randomized controlled trials with larger sample sizes.

Lum DW, Perel P, Hingorani AD, Holmes MV
CYP2D6 genotype and tamoxifen response for breast cancer: a systematic review and meta-analysis.
PLoS One. 2013; 8(10):e76648 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
OBJECTIVE: To evaluate evidence on the association between CYP2D6 genotype and tamoxifen response through.
DESIGN: Systematic review and meta-analysis of prospective, cross-sectional and case-control studies published to 2012. For each study, relative risks and 95% confidence intervals were extracted and pooled with a fixed and random effects model. Heterogeneity, publication bias, subgroup, and meta-regression analyses were performed.
DATA SOURCES: PubMed (inception-2012) and EMBASE (inception-2012).
ELIGIBILITY CRITERIA FOR SELECTING STUDIES: Criteria for inclusion were studies reporting breast cancer outcomes in patients treated with tamoxifen and genotyped for polymorphisms in the CYP2D6 gene.
RESULTS: Twenty-five studies of 13,629 individuals were identified, of which 22 investigated the association of CYP2D6 genotype with outcomes in breast cancer women all receiving tamoxifen treatment ("treatment-only" design). Three randomized trials evaluated the effect of CYP2D6 genotype on tamoxifen response ("effect modification" design). In analysis of treatment-only studies, the relative risk (RR) of all-cause mortality (>307 events in 4,936 patients) for carriers of a CYP2D6 reduced function allele was 1.11 (95% confidence interval (CI): 0.94 to 1.31) compared to individuals with normal/increased function CYP2D6 alleles. When we investigated a composite outcome including all-cause mortality and surrogate endpoints for overall survival (>307 events in 6,721 patients), carriers of a CYP2D6 reduced function allele had a RR of 1.27 (95% CI: 1.11 to 1.45). From two randomized trials that permitted effect-modification analysis, one had only 154 patients and showed evidence of effect modification of tamoxifen by CYP2D6 genotype for distant recurrence but was directionally opposite to that predicted, whereas a larger trial of 2,537 patients failed to show evidence of effect modification for breast cancer-free interval (P values for interaction 0.02 and 0.44, respectively).
CONCLUSIONS: Based on these findings, there is insufficient evidence to recommend CYP2D6 genotyping to guide tamoxifen treatment.

Li J, Czene K, Brauch H, et al.
Association of CYP2D6 metabolizer status with mammographic density change in response to tamoxifen treatment.
Breast Cancer Res. 2013; 15(5):R93 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
INTRODUCTION: Not all breast cancer patients respond to tamoxifen treatment, possibly due to genetic predisposition. As tamoxifen-induced reductions in percent mammographic density (PMD) have been linked to the risk and prognosis of breast cancer, we conducted a candidate gene study to investigate the association between germline CYP2D6 polymorphisms and PMD change.
METHODS: Baseline and follow-up mammograms were retrieved for 278 tamoxifen-treated subjects with CYP2D6 metabolizer status (extensive (EM), heterozygous extensive/intermediate (hetEM/IM) or poor metabolizer (PM)). Logistic regression analyses were conducted comparing subjects who experienced >10% reduction in PMD to those who experienced ≤10% reduction or increase.
RESULTS: After multivariate adjustment, PMD change was found to be significantly associated with the degree of CYP2D6 enzyme functionality (Ptrend = 0.021). Compared with EM, hetEM/IM and PM were 72% (95% confidence interval (CI): 0.10 to 0.79) and 71% (0.03 to 2.62) less likely to experience a >10% reduction, respectively.
CONCLUSIONS: Tamoxifen-induced change in PMD appears to have a genetic component.

Alcazar-González GA, Calderón-Garcidueñas AL, Garza-Rodríguez ML, et al.
Comparative study of polymorphism frequencies of the CYP2D6, CYP3A5, CYP2C8 and IL-10 genes in Mexican and Spanish women with breast cancer.
Pharmacogenomics. 2013; 14(13):1583-92 [PubMed] Related Publications
AIM: Pharmacogenetic studies in breast cancer (BC) may predict the efficacy of tamoxifen and the toxicity of paclitaxel and capecitabine. We determined the frequency of polymorphisms in the CYP2D6 gene associated with activation of tamoxifen, and those of the genes CYP2C8, CYP3A5 and DPYD associated with toxicity of paclitaxel and capecitabine. We also included a IL-10 gene polymorphism associated with advanced tumor stage at diagnosis.
PATIENTS & METHODS: Genomic DNAs from 241 BC patients from northeast Mexico were genotyped using DNA microarray technology.
RESULTS: For tamoxifen processing, CYP2D6 genotyping predicted that 90.8% of patients were normal metabolizers, 4.2% ultrarapid, 2.1% intermediate and 2.9% poor metabolizers. For paclitaxel and the CYP2C8 gene, 75.3% were normal, 23.4% intermediate and 1.3% poor metabolizers. Regarding the DPYD gene, only one patient was a poor metabolizer. For the IL-10 gene, 47.1% were poor metabolizers.
CONCLUSION: These results contribute valuable information towards personalizing BC chemotherapy in Mexican women.

Feld R, Woo MM, Leighl N, et al.
A clinical investigation of inhibitory effect of panobinostat on CYP2D6 substrate in patients with advanced cancer.
Cancer Chemother Pharmacol. 2013; 72(4):747-55 [PubMed] Related Publications
PURPOSE: Panobinostat is a potent oral pan-deacetylase inhibitor with promising clinical activity in hematologic malignancies. Panobinostat was shown to inhibit CYP2D6 activity in vitro; thus understanding the magnitude of the potential clinical inhibition of panobinostat on co-medications that are CYP2D6 substrates becomes important.
METHODS: This study evaluated the effects of co-administration of panobinostat with a sensitive CYP2D6 substrate, dextromethorphan (DM), in patients with advanced cancer who have functional CYP2D6 genes. Patients received 60 mg DM alone on day 1, panobinostat at 20 mg alone on days 3 and 5, and both agents on day 8. Plasma concentrations of DM and its metabolite dextrorphan (DX) were determined by liquid chromatography-tandem mass spectrometry following serial blood collections on day 1 (DM alone) and day 8 (in combination with panobinostat).
RESULTS: Panobinostat increased DM exposure by 64 % [geometric mean ratio (GMR), 1.64 (90 % confidence interval (CI), 1.17-2.31)] and DX exposure by 29 % (GMR, 1.29 [90 % CI, 1.10-1.51]). These results indicated that panobinostat weakly inhibited a sensitive CYP2D6 substrate in cancer patients by increasing DM exposure by less than twofold.
CONCLUSION: Safety monitoring of sensitive CYP2D6 substrates with narrow therapeutic index is recommended when co-administering with panobinostat in future clinical practice.

Fernández-Santander A, Gaibar M, Novillo A, et al.
Relationship between genotypes Sult1a2 and Cyp2d6 and tamoxifen metabolism in breast cancer patients.
PLoS One. 2013; 8(7):e70183 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
Tamoxifen is a pro-drug widely used in breast cancer patients to prevent tumor recurrence. Prior work has revealed a role of cytochrome and sulfotransferase enzymes in tamoxifen metabolism. In this descriptive study, correlations were examined between concentrations of tamoxifen metabolites and genotypes for CYP2D6, CYP3A4, CYP3A5, SULT1A1, SULT1A2 and SULT1E1 in 135 patients with estrogen receptor-positive breast cancer. Patients were genotyped using the Roche-AmpliChip® CYP450 Test, and Real-Time and conventional PCR-RFLP. Plasma tamoxifen, 4-hydroxy-tamoxifen, N-desmethyl-tamoxifen, endoxifen and tamoxifen-N-oxide were isolated and quantified using a high-pressure liquid chromatography-tandem mass spectrometry system. Significantly higher endoxifen levels were detected in patients with the wt/wt CYP2D6 compared to the v/v CYP2D6 genotype (p<0.001). No differences were detected in the remaining tamoxifen metabolites among CYP2D6 genotypes. Patients featuring the SULT1A2*2 and SULT1A2*3 alleles showed significantly higher plasma levels of 4-hydroxy-tamoxifen and endoxifen (p = 0.025 and p = 0.006, respectively), as likely substrates of the SULT1A2 enzyme. Our observations indicate that besides the CYP2D6 genotype leading to tamoxifen conversion to potent hydroxylated metabolites in a manner consistent with a gene-dose effect, SULT1A2 also seems to play a role in maintaining optimal levels of both 4-hydroxy-tamoxifen and endoxifen.

Dezentjé VO, van Schaik RH, Vletter-Bogaartz JM, et al.
CYP2D6 genotype in relation to tamoxifen efficacy in a Dutch cohort of the tamoxifen exemestane adjuvant multinational (TEAM) trial.
Breast Cancer Res Treat. 2013; 140(2):363-73 [PubMed] Related Publications
The clinical importance of CYP2D6 genotype as predictor of tamoxifen efficacy is still unclear. Recent genotyping studies on CYP2D6 using DNA derived from tumor blocks have been criticized because loss of heterozygosity (LOH) in tumors may lead to false genotype assignment. Postmenopausal early breast cancer patients who were randomized to receive tamoxifen, followed by exemestane in a large randomized controlled trial were genotyped for five CYP2D6 alleles. CYP2D6 genotypes and phenotypes were related to disease-free survival during tamoxifen use (DFS-t) in 731 patients. By analyzing microsatellites flanking the CYP2D6 gene, patients whose genotyping results were potentially affected by LOH were excluded. In addition, exploratory analyses on 24 genetic variants of other metabolic enzymes and the estrogen receptor were performed. For the CYP2D6 analysis, only 2.3 % of the samples were excluded, because influence of LOH could not be ruled out. No association was found between the CYP2D6 genotype or predicted phenotype and DFS-t (poor vs. extensive metabolizers: unadjusted hazard ratio 1.33, 95 % CI 0.52-3.43; P = 0.55). DFS-t was associated with UGT2B15*2 (Vt/Vt + Wt/Vt vs. Wt/Wt: adjusted hazard ratio 0.47, 95 % CI 0.25-0.89; P = 0.019) and the estrogen receptor-1 polymorphism ESR1 PvuII (gene-dose effect: adjusted hazard ratio 1.63, 95 % CI 1.04-2.54; P = 0.033). In postmenopausal early breast cancer patients treated with adjuvant tamoxifen followed by exemestane neither CYP2D6 genotype nor phenotype did affect DFS-t. This is in accordance with two recent studies in the BIG1-98 and ATAC trials. Our study is the first CYP2D6 association study using DNA from paraffin-embedded tumor tissue in which potentially false interpretation of genotyping results because of LOH was excluded. Polymorphisms in the estrogen receptor-1 and UGT2B15 may be associated with tamoxifen efficacy, but these findings need replication.

Mihály Z, Kormos M, Lánczky A, et al.
A meta-analysis of gene expression-based biomarkers predicting outcome after tamoxifen treatment in breast cancer.
Breast Cancer Res Treat. 2013; 140(2):219-32 [PubMed] Related Publications
To date, three molecular markers (ER, PR, and CYP2D6) have been used in clinical setting to predict the benefit of the anti-estrogen tamoxifen therapy. Our aim was to validate new biomarker candidates predicting response to tamoxifen treatment in breast cancer by evaluating these in a meta-analysis of available transcriptomic datasets with known treatment and follow-up. Biomarker candidates were identified in Pubmed and in the 2007-2012 ASCO and 2011-2012 SABCS abstracts. Breast cancer microarray datasets of endocrine therapy-treated patients were downloaded from GEO and EGA and RNAseq datasets from TCGA. Of the biomarker candidates, only those identified or already validated in a clinical cohort were included. Relapse-free survival (RFS) up to 5 years was used as endpoint in a ROC analysis in the GEO and RNAseq datasets. In the EGA dataset, Kaplan-Meier analysis was performed for overall survival. Statistical significance was set at p < 0.005. The transcriptomic datasets included 665 GEO-based and 1,208 EGA-based patient samples. All together 68 biomarker candidates were identified. Of these, the best performing genes were PGR (AUC = 0.64, p = 2.3E-07), MAPT (AUC = 0.62, p = 7.8E-05), and SLC7A5 (AUC = 0.62, p = 9.2E-05). Further genes significantly correlated to RFS include FOS, TP53, BTG2, HOXB7, DRG1, CXCL10, and TPM4. In the RNAseq dataset, only ERBB2, EDF1, and MAPK1 reached statistical significance. We evaluated tamoxifen-resistance genes in three independent platforms and identified PGR, MAPT, and SLC7A5 as the most promising prognostic biomarkers in tamoxifen treated patients.

Serrano D, Lazzeroni M, Gandini S, et al.
A randomized phase II presurgical trial of weekly low-dose tamoxifen versus raloxifene versus placebo in premenopausal women with estrogen receptor-positive breast cancer.
Breast Cancer Res. 2013; 15(3):R47 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
INTRODUCTION: We previously demonstrated that 1 or 5 mg per day of tamoxifen (T) given for four weeks before surgery reduces Ki-67 in breast cancer (BC) patients to the same extent as the standard 20 mg/d. Given the long half-life of T, a weekly dose (10 mg per week (w)) may be worth testing. Also, raloxifene (R) has shown Ki-67 reduction in postmenopausal patients in a preoperative setting, but data in premenopausal women are limited. We conducted a randomized trial testing T 10 mg/w vs. R 60 mg/d vs. placebo in a presurgical model.
METHODS: Out of 204 screened subjects, 57 were not eligible, 22 refused to participate and 125 were included in the study. The participants were all premenopausal women with estrogen receptor-positive BC. They were randomly assigned to either T 10mg/w or R 60 mg/d or placebo for six weeks before surgery. The primary endpoint was tissue change of Ki-67. Secondary endpoints were modulation of estrogen and progesterone receptors and several other circulating biomarkers.
RESULTS: Ki-67 was not significantly modulated by either treatment. In contrast, both selective estrogen receptor modulators (SERMs) significantly modulated circulating IGF-I/IGFBP-3 ratio, cholesterol, fibrinogen and antithrombin III. Estradiol was increased with both SERMs. Within the tamoxifen arm, CYP2D6 polymorphism analysis showed a higher concentration of N-desTamoxifen, one of the tamoxifen metabolites, in subjects with reduced CYP2D6 activity. Moreover, a reduction of Ki-67 and a marked increase of sex hormone-binding globulin (SHBG) were observed in the active phenotype.
CONCLUSIONS: A weekly dose of tamoxifen and a standard dose of raloxifene did not inhibit tumor cell proliferation, measured as Ki-67 expression, in premenopausal BC patients. However, in the tamoxifen arm women with an extensive phenotype for CYP2D6 reached a significant Ki-67 modulation.

Zafra-Ceres M, de Haro T, Farez-Vidal E, et al.
Influence of CYP2D6 polymorphisms on serum levels of tamoxifen metabolites in Spanish women with breast cancer.
Int J Med Sci. 2013; 10(7):932-7 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
BACKGROUND: Estrogen receptor-positive breast cancer tumors depend on estrogen signaling for their growth and replication and can be treated by anti-estrogen therapy with tamoxifen. Polymorphisms of the CYP2D6 and CYP2C19 genes are associated with an impaired response to tamoxifen. The study objective was to investigate the impact of genetic polymorphisms in CYP2D6 and CYP2C19 on the pharmacokinetics of tamoxifen and its metabolites in Spanish women with estrogen receptor-positive breast cancer who were candidates for tamoxifen therapy.
METHODS: We studied 90 women with estrogen receptor-positive breast cancer, using the AmpliChip CYP450 test to determine CYP2D6 and CYP2C19 gene variants. Plasma levels of tamoxifen and its metabolites were quantified by high-performance liquid chromatography.
RESULTS: The CYP2D6 phenotype was extensive metabolizer in 80%, intermediate metabolizer in 12.2%, ultra-rapid metabolizer in 2.2%, and poor metabolizer in 5.6% of patients, and the allele frequency was 35.0% for allele (*)1, 21.0% for *2, and 18.9% for *4. All poor metabolizers in this series were *4/*4, and their endoxifen and 4-hydroxy tamoxifen levels were 25% lower than those of extensive metabolizers. CYP2C19*2 allele, which has been related to breast cancer outcomes, was detected in 15.6% of the studied alleles.
CONCLUSION: CYP2D6*4/*4 genotype was inversely associated with 4-hydroxy tamoxifen and endoxifen levels. According to these results, CYP2D6 and CYP2C19 genotyping appears advisable before the prescription of tamoxifen therapy.

Awada Z, Haider S, Tfayli A, et al.
Pharmacogenomics variation in drug metabolizing enzymes and transporters in relation to docetaxel toxicity in Lebanese breast cancer patients: paving the way for OMICs in low and middle income countries.
OMICS. 2013; 17(7):353-67 [PubMed] Related Publications
We investigated the association of genetic polymorphisms in drug metabolizing enzymes (DMEs) and transporters in patients with docetaxel-induced febrile neutropenia, by a new high-throughput DMEs and transporters (DMETPlus) microarray platform, characterizing 1936 single nucleotide polymorphisms (SNPs) in 225 genes. We recruited 100 Lebanese breast cancer patients from a consecutive cohort of 277 patients who received docetaxel either alone, or in combination with trastuzumab. Out of 100 patients, 18 had developed febrile neutropenia (cases). They were age- and treatment- matched with 18 patients who did not develop febrile neutropenia on docetaxel (controls). We found that 12 SNPs in seven genes (ABCC6, ABCG1, ABCG2, CYP1A2, CYP2D6, FMO2, and FMO3) were significantly associated with febrile neutropenia after docetaxel treatment. Many of these SNPs have not been previously reported to be associated with toxicity due to docetaxel treatment. Interestingly, one SNP in the FMO3 gene (rs909530) was significantly associated with three clinical endpoints: febrile neutropenia, reduced absolute neutrophil count, and hemoglobin reduction. To the best of our knowledge, this is the first study that evaluated the effect of a large array of nearly 2000 polymorphisms in DMEs and transporters on docetaxel toxicity in breast cancer patients, and in a previously understudied population. Additionally, it attests to the feasibility of genomics research in low- and middle-income countries (LMICs). In light of the current global epidemic of noncommunicable diseases (NCDs) such as breast cancer impacting LMICs, we suggest pharmacogenomics is considered as an integral part of the global health research agenda for NCDs and personalized therapeutics.

Zeng Z, Liu Y, Liu Z, et al.
CYP2D6 polymorphisms influence tamoxifen treatment outcomes in breast cancer patients: a meta-analysis.
Cancer Chemother Pharmacol. 2013; 72(2):287-303 [PubMed] Related Publications
PURPOSE: To evaluate whether breast cancer (BC) patients with CYP2D6 gene variation have different clinical tamoxifen (TAM) treatment outcomes to those with normal function of CYP2D6.
METHODS: Systematic searches of the PubMed up to February 21, 2013, were retrieved. The study end points were disease-free survival (DFS) and overall survival (OS). Fixed or random-effects meta-analytical models were used to calculate summary hazard ratio (HR) and corresponding 95 % confidence intervals (CIs). Meta-regression, Galbraith plots, subgroup analysis, and sensitivity analysis were also performed.
RESULTS: A total of 11,701 BC patients from 20 trials were included. Compared with reduced CYP2D6 function, normal function was associated with a trend toward improved DFS (HR = 1.37, 95 % CI 1.12-1.69, P = 0.002) and OS (HR = 1.25, 95 % CI 1.03-1.50, P = 0.021). We found significant heterogeneity between studies. When the analysis was stratified into subgroups, significantly worse DFS was found in the groups of intermediate metabolizer versus extensive metabolizer (HR = 1.65, 95 % CI 1.04-2.64, P = 0.035), Asian population (HR = 3.29, 95 % CI 1.64-6.63, P = 0.001), 5 years TAM treatment duration (HR = 1.59; 95 % CI 1.14-2.22, P = 0.006), concomitant chemotherapy (HR = 1.35, 95 % CI 1.04-1.76, P = 0.025), and TAM alone (HR = 1.44, 95 % CI 1.44-2.06, P = 0.045). With respect to OS, no significant association was demonstrated in stratified analyses.
CONCLUSIONS: We concluded that CYP2D6 polymorphisms may influence tamoxifen treatment outcomes of DFS in BC patients.

Karle J, Bolbrinker J, Vogl S, et al.
Influence of CYP2D6-genotype on tamoxifen efficacy in advanced breast cancer.
Breast Cancer Res Treat. 2013; 139(2):553-60 [PubMed] Related Publications
The influence of CYP2D6 genotype on the efficacy of tamoxifen (Tam) has been extensively analyzed in early breast cancer with conflicting results. However, there is only scarce data regarding this potential influence in advanced breast cancer (ABC). We hypothesize that Tam is more effective in patients with a functional CYP2D6 allele than in patients with impaired CYP2D6 activity. ABC patients with prior or ongoing palliative Tam treatment (20 mg/d) were eligible. Genomic DNA was extracted from blood (n = 51) and formalin-fixed, paraffin-embedded tissue (n = 43). CYP2D6*2, *3, *4, *5, *6, *10, *17, *29, *41, CYP2D6 duplication and multiplication were determined in blood and CYP2D6*4 in tissue samples. Primary endpoint was progression free survival (PFS); secondary endpoints included clinical benefit (CB), and overall survival (OS). The clinical charts were retrospectively analyzed regarding survival and treatment effects. Genotyping was performed blinded and clinical data were analyzed separately. 94 patients were identified with a median age of 59 years (29-90 years). In 6 patients genotyping did not show conclusive results, therefore these patients were excluded from further analysis. Genotyping results were as follows: 1.1 % ultrarapid, 84.1 % extensive, 3.4 % intermediate, and 11.4 % poor metabolizers. Patients without any fully functional allele (IM/IM, IM/PM, PM/PM) had a significant shorter PFS and OS compared to patients with at least one functional allele (EM/EM, EM/IM, EM/PM) (PFS: p = 0.017; HR = 2.19; 95 % CI 1.15-4.18; OS: p = 0.028; HR = 2.79; 95 % CI 1.12-6.99). The CB rate was 73 % for EM-group and 38.5 % for IM + PM-group (p = 0.019). Our results show a significant influence of the CYP2D6 genotype on the efficacy of Tam in the treatment of ABC. In contrast to the adjuvant setting, the evidence in the palliative setting is congruent. CYP2D6 testing in ABC should be considered.

Takimoto T, Kijima T, Otani Y, et al.
Polymorphisms of CYP2D6 gene and gefitinib-induced hepatotoxicity.
Clin Lung Cancer. 2013; 14(5):502-7 [PubMed] Related Publications
INTRODUCTION: Gefitinib induces severe hepatotoxicity in approximately a quarter of Japanese patients with epidermal growth factor receptor (EGFR) mutation-positive non-small-cell lung cancer (NSCLC). Gefitinib is metabolized by cytochrome P450 (CYP) enzymes--including CYP3A4/5, CYP1A1, and CYP2D6--in the liver. We hypothesized that polymorphisms of the CYP2D6 gene may account for gefitinib-induced hepatotoxicity.
PATIENTS AND METHODS: Polymorphisms of the CYP2D6 gene were analyzed in 55 patients with NSCLC who experienced grade ≥ 2 transaminase elevation from gefitinib. The distribution of the CYP2D6 genotype was compared with that of the healthy Japanese population. The correlations between the nonfunctional allele *5 or the reduced-function allele *10 and hepatotoxicity-related clinical factors were also examined.
RESULTS: The distribution of the CYP2D6 genotype in the study participants was not different from that of the general Japanese population, reported previously. Existence of allele *5 or *10 did not correlate with clinical factors such as onset of hepatotoxicity within 2 months, grade ≥ 3 serum transaminase elevation, and tolerability to dose reduction or rechallenge of gefitinib. However, in 7 patients taking CYP3A4-inhibitory drugs, rechallenge of gefitinib again caused hepatotoxicity in 4 patients with allele *5 or *10 but not in 3 patients with normal alleles (P = .029). Moreover, switching to erlotinib did not cause hepatotoxicity in any of 17 patients with allele *5 or *10 but did in 3 of 8 patients without these alleles (P = .024).
CONCLUSION: Reduced function of CYP2D6 may partly account for gefitinib-induced hepatotoxicity when CYP3A4 is inhibited. Erlotinib could be safely used in patients with decreased CYP2D6 activity even after they experienced gefitinib-induced hepatotoxicity.

Huang Y, Liu X, Kuang X, Liao D
CYP2D6 T188C variant is associated with lung cancer risk in the Chinese population.
Tumour Biol. 2013; 34(4):2189-93 [PubMed] Related Publications
The CYP2D6 gene has been suggested to play an important role in the pathogenesis of lung cancer. However, the results have been inconsistent. In this study, we performed a meta-analysis to clarify the association of CYP2D6 T188C variant with lung cancer. Published literature from PubMed, Embase, Chinese National Knowledge Infrastructure and Wanfang data were retrieved. Pooled odds ratio (OR) with 95 % confidence interval (CI) was calculated using fixed- or random-effects model. A total of nine studies (1,516 lung cancer cases and 1,950 controls) for CYP2D6 T188C variant were included in the meta-analysis. The meta-analysis indicated that compared with CYP2D6 TT genotype, non-TT genotype (CC or CT) was significantly associated with lung cancer in the Chinese (OR = 1.61, 95 % CI = 1.38-1.87, p < 0.001), with no evidence of between-study heterogeneity (I (2) = 0.0 %, p = 0.991). The sensitivity analysis indicated that the association was stable and no publication bias was detected. The present meta-analysis supported the positive association of CYP2D6 T188C variant with lung cancer in the Chinese. Further large-scale studies with the consideration for gene-gene/gene-environment interactions should be conducted to investigate the association.

Huang FM, Chen HC, Khan MA, et al.
CYP2A6, CYP1A1, and CYP2D6 polymorphisms in lung cancer patients from central south China.
Med Oncol. 2013; 30(2):521 [PubMed] Related Publications
Lung cancer is a common cause of cancer-related death. The link between risk of lung cancer susceptibility and genetic polymorphisms in metabolic enzymes is well documented. In this study, the relationships between lung cancer susceptibility and polymorphisms in the phase I metabolic enzyme genes CYP1A1, CYP2D6, and CYP2A6 were investigated. Genomic DNA was isolated from the peripheral blood of 201 healthy controls and 168 lung carcinoma patients from the Han ethnic group of Hunan Province in Central South China. Polymorphisms of the investigated genes were analyzed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and two-step allelic-specific PCR assays. No significant differences were found between the frequencies in cases and controls for the genotypes wild-type (WW), heterozygous mutant, or homozygous mutant; for CYP1A1 or CYP2D6; or for the genotypes WW, heterozygous deletion, or null genotype for CYP2A6. The three-locus model (CYP2A6/CYP1A1/CYP2D6) had a maximum test sample accuracy that was significant (P < 0.001) with a cross-validation consistency of 10. These results indicated that the three-order interaction of CYP2A6, CYP1A1, and CYP2D6 polymorphisms might increase genetic susceptibility to lung cancer. We report the involvement of a three-order interaction between CYP1A1, CYP2A6, and CYP2D6 polymorphisms in lung cancer risk in people in Central South China, although no relationship between lung cancer risk and individual gene polymorphisms was found.

Altés A, Paré L, Esquirol A, et al.
Pharmacogenetic analysis in the treatment of Hodgkin lymphoma.
Leuk Lymphoma. 2013; 54(8):1706-12 [PubMed] Related Publications
About 15-20% of patients with Hodgkin lymphoma (HL) treated with doxorubicin, bleomycin, vinblastine and dacarbazine (ABVD) chemotherapy ± radiotherapy still die following relapse or progressive disease. The outcome might be influenced by gene polymorphisms influencing chemotherapy metabolism. We studied 126 patients with HL treated with the ABVD regimen. We analyzed glutathione S-transferases (GSTT1, GSTM1 and GSTP1), cytochromes P450 (CYP3A4 and CYP2D6), UGT1A1 and BLMH gene polymorphisms and their association with clinical and outcome variables. Patients with a GSTM1 genotype associated with extensive or ultrahigh activity had a probability of 93.8% to achieve a complete response, while the remainder of the patients had a probability of 82.3% (p = 0.04). This variable maintained its statistical significance in multivariate analysis (hazard ratio 3.7, 95% confidence interval 1-13, p = 0.05). Patients with an extensive or ultrahigh GSTM1 genotype had better prognostic factors than those with poor or intermediate genotypes (hemoglobin level, p = 0.003; serum albumin, p = 0.05; and International Prognostic Score, p = 0.038). Thus, in the treatment of HL, clinical determinants might be more relevant than the pharmacogenetic parameters analyzed to date.

Rolla R, Vidali M, Meola S, et al.
Side effects associated with ultrarapid cytochrome P450 2D6 genotype among women with early stage breast cancer treated with tamoxifen.
Clin Lab. 2012; 58(11-12):1211-8 [PubMed] Related Publications
BACKGROUND: The side effects of tamoxifen, a drug widely used for the treatment and the prevention of recurrence in patients with estrogen receptor positive breast cancers (ER+), have been reported in clinical trials, but to date no information is available on their possible association with an increased enzymatic activity of CYP2D6 (ultra-metabolizers, UMs). The aim of this study was therefore to evaluate the association between the presence of multiple functional CYP2D6 alleles and the occurrence of side effects.
METHODS: 61 women with ER+ breast cancer receiving tamoxifen monotherapy were investigated in order to assess the relationships between CYP2D6 UM phenotype and side effects. Genotyping of 16 CYP2D6 polymorphisms was performed using a new DNA microarray technology.
RESULTS: A highly significant difference was detected (41.2% of difference, 95% CI 6 - 61%, Fisher's exact test, p = 0.030) between the numbers of Ultrarapid Metabolizer patients (UM; high activity) with two or more adverse drug reactions to tamoxifen (7/9; 77.8%), compared to the number of Extensive Metabolizers (EM; normal activity), Intermediate Metabolizers (IM; reduced activity), and Poor Metabolizers (PM; no activity) with at least two side effects (19/52, 36.5%). A similar difference was also observed comparing the two groups (UM vs EM-IM-PM) for the number of side effects (median and inter quartile range, IQR: AM/EM/IM 1, IQR 0-2 vs. ULTRA 2, IQR 2-4; Mann-Whitney p = 0.005).
CONCLUSIONS: Our results suggest a new association between CYP2D6 gene duplication and side effects to tamoxifen, indicating a possible role of CYP2D6 in their occurrence.

Opdam FL, Dezentje VO, den Hartigh J, et al.
The use of the 13C-dextromethorphan breath test for phenotyping CYP2D6 in breast cancer patients using tamoxifen: association with CYP2D6 genotype and serum endoxifen levels.
Cancer Chemother Pharmacol. 2013; 71(3):593-601 [PubMed] Related Publications
PURPOSE: Adjuvant therapy with tamoxifen significantly reduces breast cancer recurrence and mortality in estrogen receptor positive disease. CYP2D6 is the main enzyme involved in the activation of the prodrug tamoxifen into the anti-estrogen endoxifen. Endoxifen is thought to be a main determinant for clinical efficacy in breast cancer patients using tamoxifen. As the large interindividual variation in endoxifen levels is only partly explained by CYP2D6 genotype, we explored the use of the (13)C-dextromethorphan breath test (DM-BT) for phenotyping CYP2D6 and to predict serum steady-state endoxifen levels as a marker for clinical outcome in breast cancer patients using tamoxifen.
METHODS: In 65 patients with early breast cancer using tamoxifen, CYP2D6 phenotype was assessed by DM-BT. CYP2D6 genotype using Amplichip and serum steady-state levels of endoxifen were determined. Genotype was translated into the gene activity score and into ultrarapid, extensive, heterozygous extensive, intermediate or poor metabolizer CYP2D6 predicted phenotype.
RESULTS: CYP2D6 phenotype determined by the DM-BT explained variation in serum steady-state endoxifen levels for 47.5% (R(2) = 0.475, p < 0.001). Positive and negative predictive values for a recently suggested threshold serum level of endoxifen (5.97 ng/mL) for breast cancer recurrence rate were 100 and 90%, respectively, for both CYP2D6 phenotype by DM-BT (delta-over-baseline at t = 50 min (DOB(50)) values of 0.7-0.9) and genotype (CYP2D6 gene activity score of 1.0).
CONCLUSION: DM-BT might be, along with CYP2D6 genotyping, of value in selection of individualized endocrine therapy in patients with early breast cancer, especially when concomitant use of CYP2D6 inhibiting medication alters the phenotype.

Goetz MP, Suman VJ, Hoskin TL, et al.
CYP2D6 metabolism and patient outcome in the Austrian Breast and Colorectal Cancer Study Group trial (ABCSG) 8.
Clin Cancer Res. 2013; 19(2):500-7 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
PURPOSE: Controversy exists about CYP2D6 genotype and tamoxifen efficacy.
EXPERIMENTAL DESIGN: A matched case-control study was conducted using the Austrian Breast and Colorectal Cancer Study Group Trial 8 (ABCSG8) that randomized postmenopausal women with estrogen receptor (ER)-positive breast cancer to tamoxifen for 5 years (arm A) or tamoxifen for 2 years followed by anastrozole for 3 years (arm B). Cases had disease recurrence, contralateral breast cancer, second non-breast cancer, or died. For each case, controls were identified from the same treatment arm of similar age, surgery/radiation, and tumor-node-metastasis (TNM) stage. Genotyping was conducted for alleles associated with no (PM; *3, *4, *6), reduced (IM; *10, and *41), and extensive (EM: absence of these alleles) CYP2D6 metabolism.
RESULTS: The common CYP2D6*4 allele was in Hardy-Weinberg equilibrium. In arm A during the first 5 years of therapy, women with two poor alleles [PM/PM: OR, 2.45; 95% confidence interval (CI), 1.05-5.73, P = 0.04] and women with one poor allele (PM/IM or PM/EM: OR, 1.67; 95% CI, 0.95-2.93; P = 0.07) had a higher likelihood of an event than women with two extensive alleles (EM/EM). In years 3 to 5 when patients remained on tamoxifen (arm A) or switched to anastrozole (arm B), PM/PM tended toward a higher likelihood of a disease event relative to EM/EM (OR, 2.40; 95% CI, 0.86-6.66; P = 0.09) among women on arm A but not among women on arm B (OR, 0.28; 95% CI, 0.03-2.30).
CONCLUSION: In ABCSG8, the negative effects of reduced CYP2D6 metabolism were observed only during the period of tamoxifen administration and not after switching to anastrozole.

Sukasem C, Sirachainan E, Chamnanphon M, et al.
Impact of CYP2D6 polymorphisms on tamoxifen responses of women with breast cancer: a microarray-based study in Thailand.
Asian Pac J Cancer Prev. 2012; 13(9):4549-53 [PubMed] Related Publications
This study was designed to investigate the frequency of CYP2D6 polymorphisms and evaluate the association between genetic polymorphisms of CYP2D6 and tamoxifen therapeutic outcome in Thai breast cancer patients. We recruited 48 breast cancer patients who received adjuvant tamoxifen for evaluating CYP2D6 genetic polymorphisms using microarray-based technology. Associations between genotypes-phenotypes and disease free survival were analyzed. Median follow up time was 5.6 years. The mean age of the subjects was 50 years. The 3 common allelic frequencies were 43.8% (*10), 36.5 (*1) and 10.4% (*2) which are related to extensive metabolizer (EM) and intermediate metabolizer (IM) with 70.8% and 29.2 %, respectively. No association between CYP2D6 genotypes and DFS was demonstrated. Nevertheless, exploratory analysis showed statistically significant shorter DFS in the IM group of post-menopause patients (HR, 6.85; 95% CI, 1.48 -31.69; P = 0.005). Furthermore, we observed statistically significant shorter DFS of homozygous CYP2D6*10 when compared with heterozygous CYP2D6*10 and other genotypes (P=0.005). CYP2D6*10 was the most common genotype in our subjects. Post-menopause patients with homozygous CYP2D6*10 and IM have shorter DFS. To confirm this relationship, larger samples and comprehensively designed trials in Thailand are required.

Seong SJ, Lim M, Sohn SK, et al.
Influence of enzyme and transporter polymorphisms on trough imatinib concentration and clinical response in chronic myeloid leukemia patients.
Ann Oncol. 2013; 24(3):756-60 [PubMed] Related Publications
BACKGROUND: This study explored the impact of genetic polymorphisms in cytochrome P450 (CYP) enzymes and transporters on the plasma trough concentration of imatinib mesylate (IM) and clinical response in chronic myeloid leukemia (CML).
PATIENTS AND METHODS: In total, 82 patients with CML who had been administered 400 mg IM daily for over 6 months were genotyped for 11 single-nucleotide polymorphisms in nine genes (CYP3A4, CYP3A5, CYP2C9, CYP2C19, CYP2D6, ABCB1, SLC22A1, SLC22A2 and ABCG2) using blood samples. The trough imatinib concentration and clinical responses were assessed 6 months after the initiation of IM therapy.
RESULTS: The CC, CA and AA genotypes in ABCG2 421C>A gave significantly different frequencies for the major molecular response (MMR) (P = 0.02). However, no significant differences were found between the genotypes of the CYP enzymes and transporters identified in this study and the imatinib plasma trough concentrations and clinical response frequencies, except for the correlation of ABCG2 with MMR.
CONCLUSIONS: The results of the present study may indicate that the ABCG 421C>A genetic polymorphism influences the MMR of imatinib in patients with CML.

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