Endoxifen Concentrations Research Articles

Effects of CYP2D6*10 polymorphism on tamoxifen pharmacokinetics in patients with breast cancer in Asia: a meta-analysis.

Insufficient serum metabolite concentrations of tamoxifen can compromise treatment efficacy in patients with breast cancer. The purpose of this meta-analysis was to explore correlations between cytochrome P450 (CYP) 2D6*10 gene polymorphisms and serum concentrations of tamoxifen and its active metabolites in patients with breast cancer in Asia. The study included a systematic literature search for cohort studies published before March 2018 in English databases (PubMed, Embase, Cochrane Library, and Web of Science) and Chinese databases (Chinese National Knowledge Infrastructure and Wan Fang database). The meta-analysis was performed using RevMan 5.3 software. Pooled means and standard deviations were calculated with 95% confidence intervals. Publication bias and sensitivity analyses were also performed using STATA 14.0. In total, 7 studies and 552 patients were included in the meta-analysis. Serum concentrations of endoxifen were significantly different in each CYP2D6*10 genotype group (p < 0.05). The CC genotype was associated with higher concentrations of 4-OH-TAM than the CT/TT genotype (p < 0.05). However, there were no statistically significant between-group differences in serum concentrations of TAM (p > 0.05). Publication bias and sensitivity analyses confirmed that the meta-analysis results were stable and reliable. CYP2D6*10 polymorphisms influence the pharmacokinetics of tamoxifen in patients with breast cancer in Asia.

PCN191 - COST-EFFECTIVENESS OF MONITORING ENDOXIFEN LEVELS IN BREAST CANCER PATIENTS ADJUVANTLY TREATED WITH TAMOXIFEN

Breast cancer is the most common malignancy in women worldwide. Recurrence rates in breast cancer are considered to be dependent on the serum concentration of endoxifen, the active metabolite of tamoxifen. The goal of this study is to investigate the cost-effectiveness of periodically monitoring serum concentrations of endoxifen in adjuvant estrogen receptor alfa (ERα) positive breast cancer patients treated with tamoxifen in the Netherlands. A Markov model with disease free survival (DFS), recurrent disease (RD) and death states was constructed. The benefit of drug monitoring was modeled via a difference in the fraction of patients achieving adequate serum concentrations. Robustness of results to changes in model assumptions were tested through deterministic and probabilistic sensitivity analyses. Monitoring of endoxifen added 0.0115 quality-adjusted life years (QALYs) and saved € 1,564 per patient in the base case scenario. Deterministic sensitivity analysis demonstrated a large effect on the incremental cost-effectiveness ratio (ICER) of the differences in costs and utilities between the DFS and RD states. Probabilistic sensitivity analysis showed that the probability of cost-effectiveness at a willingness to pay of € 0 per quality-adjusted life year (QALY) was 89.8%. Based on this model, monitoring of endoxifen in adjuvant ERα+ breast cancer patients treated with tamoxifen is likely to add QALYs and save costs from a healthcare payer perspective. We advise clinicians to consider integrating serum endoxifen concentration monitoring into standard adjuvant tamoxifen treatment of ERα+ breast cancer patients.

258P - Incidence of clinically significant toxicities in patients with high endoxifen concentrations

258P - Incidence of clinically significant toxicities in patients with high endoxifen concentrations

Cost-effectiveness of monitoring endoxifen levels in breast cancer patients adjuvantly treated with tamoxifen

PurposeBreast cancer is the most common malignancy in women worldwide. Recurrence rates in breast cancer are considered to be dependent on the serum concentration of endoxifen, the active metabolite of tamoxifen. The goal of this study is to investigate the cost-effectiveness of periodically monitoring serum concentrations of endoxifen in adjuvant estrogen receptor alfa (ERα) positive breast cancer patients treated with tamoxifen in the Netherlands.MethodsA Markov model with disease-free survival (DFS), recurrent disease (RD), and death states was constructed. The benefit of drug monitoring was modeled via a difference in the fraction of patients achieving adequate serum concentrations. Robustness of results to changes in model assumptions were tested through deterministic and probabilistic sensitivity analyses.ResultsMonitoring of endoxifen added 0.0115 quality-adjusted life-years (QALYs) and saved € 1564 per patient in the base case scenario. Deterministic sensitivity analysis demonstrated a large effect on the incremental cost-effectiveness ratio (ICER) of the differences in costs and utilities between the DFS and RD states. Probabilistic sensitivity analysis showed that the probability of cost-effectiveness at a willingness to pay of € 0 per quality-adjusted life-year (QALY) was 89.8%.ConclusionsBased on this model, monitoring of endoxifen in adjuvant ERα + breast cancer patients treated with tamoxifen is likely to add QALYs and save costs from a healthcare payer perspective. We advise clinicians to consider integrating serum endoxifen concentration monitoring into standard adjuvant tamoxifen treatment of ERα + breast cancer patients.

CYP2D6 genotype and endoxifen plasma concentration do not predict hot flash severity during tamoxifen therapy.

Tamoxifen is frequently prescribed to prevent breast cancer recurrence. Tamoxifen is a prodrug and requires bioactivation by CYP2D6. Tamoxifen use is often limited by adverse effects including severe hot flashes. There is paucity of prospectively collected data in terms of CYP2D6 genotype and measured tamoxifen, 4-hydroxytamoxifen and endoxifen concentrations in relation to hot flash severity during tamoxifen therapy. We conducted a longitudinal prospective study of breast cancer patients on tamoxifen (n = 410). At each visit, blood samples were collected, and patients completed a standardized hot flash survey (n = 1144) that reflected hot flash severity during the 7 days prior to the visit. Plasma concentrations of tamoxifen, 4-hydroxytamoxifen, and endoxifen were measured using liquid chromatography-tandem mass spectrometry and genotyping was carried out for CYP2D6. A linear mixed-effects regression analysis assessed the association of covariates in relation to the hot flash severity score (HFSS). Median age at first assessment was 50years with 61.9% of patients considered peri-menopausal. Most patients (92.2%) experienced hot flash symptoms with 51.0% having low HFSS (0-4) and 7.32% experiencing HFSS > 25. Age was significantly associated with hot flash severity, with patients aged 45-59 more likely to have higher HFSS. Neither duration of tamoxifen therapy nor observed tamoxifen, endoxifen and 4-hydroxy tamoxifen plasma concentration predicted hot flash severity. Genetic variation in CYP2D6 or CYP3A4 was not predictive of hot flash severity. Hot flash severity during tamoxifen therapy can not be accounted for by CYP2D6 genotype or observed plasma concentration of tamoxifen, 4-hydroxytamoxifen, or endoxifen.

A prospective study on the effect of endoxifen concentration and CYP2D6 phenotypes on clinical outcome in early stage breast cancer patients receiving adjuvant tamoxifen.

523Background: It has been postulated that endoxifen levels are better predictors of tamoxifen efficacy than CYP2D6 phenotype. Although in a retrospective study an endoxifen threshold of 5.9 ng/ml ...

Tratamiento de los síntomas vasomotores en pacientes con cáncer de mama. Revisión narrativa

Las mujeres con antecedentes de cáncer de mama suelen experimentar síntomas vasomotores más severos y frecuentes que la población general. Numerosos trabajos han demostrado que los síntomas vasomotores (SVM) son los efectos adversos más frecuentes de la terapia adyuvante, y que hasta 20% de las pacientes con cáncer de mama considera discontinuar el tratamiento debido a estos síntomas, a pesar de su beneficio en la reducción de la recurrencia. Mientras que la terapia sustitutiva hormonal (THM) es usada regularmente en mujeres sanas para tratamiento de los SVM, está contraindicada en pacientes con antecedente de cáncer de mama. Existen muy pocos datos clínicos sobre las intervenciones no farmacológicas, y el papel de las terapias alternativas y complementarias sigue siendo controvertido. La revisión de la literatura da cuenta de que estos agentes farmacológicos, los inhibidores de la recaptación de serotonina-norepinefrina (IRNSs), los inhibidores selectivos de la recaptación de serotonina (IRSs), los antihipertensivos y los anticonvulsivos, disminuyen la intensidad y frecuencia de los SVM, demostrando una mejoría clínicamente significativa. Sin embargo, algunos IRSSs e IRSNs son potentes inhibidores del citocromo P450 2D6 (CYP 2D6), lo que impacta en la concentración de endoxifeno, debiendo ser evitados en pacientes tratadas con tamoxifeno. Son una opción el citalopram y la venlafaxina, si bien su consecuencia sobre la recurrencia y supervivencia del cáncer de mama es controvertida. La eficacia en el tratamiento de los SVM con antidepresivos es menor que con estrógenos y hay pocas publicaciones comparando ambos tratamientos. Faltan datos sobre el lapso de la indicación. Dos fármacos antiepilépticos también han demostrado efectividad, la gabapentina y la pregabalina. Algunas investigaciones comparativas están en curso, y habrá que esperar sus resultados para individualizar cuál es el óptimo en el manejo de los síntomas menopáusicos en mujeres que han padecido cáncer de mama.

CYP2D6 and Endoxifen in Tamoxifen Therapy: A Tribute to David A. Flockhart.

This issue of Clinical Pharmacology & Therapeutics (CPT) includes the Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for using CYP2D6 genotyping to guide tamoxifen therapy for breast cancer patients. CYP2D6 metabolizes tamoxifen to its more active metabolite, endoxifen, and patients with reduced CYP2D6 activity have reduced circulating endoxifen concentrations. In this associated commentary, we recognize and honor the late Dr. David Flockhart, who began the research and made early fundamental discoveries on tamoxifen that have now resulted in this guideline.

Abstract P3-12-03: Impact of genetic polymorphisms on plasma levels of tamoxifen and its metabolites and toxicity: 6-months results of the adjuvant breast cancer longitudinal PHACS study (NCT01127295)

Abstract Supported by a PHRC grant (#09-18-005) Background: The role of CYP2D6 genetic polymorphisms and plasma levels of active metabolites of tamoxifen (TAM) on clinical response and occurrence of side effects remains controversial. We conducted a prospective, adjuvant, multicentre, 3-year follow-up study of breast cancer patients in order to evaluate the relationships between pharmacogenetics, pharmacokinetics and toxicity of TAM and its metabolites (n=879) or aromatase inhibitors (AI, n=1098). The present report focuses on the evaluation at 6 months after inclusion of 864 patients treated with 20 mg/day TAM.The clinical results and the AI PG/PK analyses are described elsewhere (abstracts #851544 and #851525). Methods: Residual plasma concentrations for tamoxifen and its 6 major metabolites (endoxifen ENDO, 4-hydroxy-tamoxifen 4-OH-TAM, N-desmethyl TAM, TAM-N-oxyde, 4'-OH-TAM and Z'ENDO) at 6 months after start of treatment were measured by UPLC-MS/MS in 789 patients. Nine patients with TAM concentrations below the limit of quantification were excluded for non-compliance. SNP genotyping of 95 selected SNPs was performed on the Biomark (Fluidigm) in a microfluidic multiplex 96 dynamic array chip with Taqman assays and was available for 857 patients. Patients were classified according to their CYP2D6 metaboliser status (MS) (PM, IM, EM and UM) based on presence of functional, decreased function or no functional alleles (*4, *6, *7, *9, *10, *17, *41) and number of CYP2D6 copies (*5 or duplication). Metabolic ratios (MR) were calculated for TAM/4-OH-TAM, TAM/N-desmethyl tamoxifen (NDT), NDT/ENDO and 4-OH-TAM/ENDO. Anti-estrogenic activity score (AAS) was calculated according to a recently proposed algorithm (De Vries Schultink et al.,Breast Cancer Res Treat. 2017).Toxicity was measured as a binary outcome (first occurrence or worsening of hot flushes, fatigue, depression, pain, arthralgia, vaginal dryness). All genetic associations were adjusted for multiple testing. Results: ENDO concentration and AAS increased significantly with CYP2D6 MS (p&amp;lt;0.001). The presence of a CYP3A4*22 allele was significantly associated with endoxifen concentrations; this association remained significant after adjusting for CYP2D6 MS. TAM/4-OH-TAM MR was significantly influenced by the presence of CYP3A4*22, CYP2C19*2 and *17, and CYP2D6 status. The percentage of patients having an AAS&amp;gt;=1798 (i.e., threshold previously associated with recurrence-free survival RFS by De Vries et al. 2017) was 6%, 50%, 84% and 91% of patients respectively classified as PM, IM, EM and UM. Side effects were not significantly associated with higher levels of TAM metabolites concentrations. After correction for multiple testing, SNPs or CYP2D6 MS were not significantly associated with occurrence or worsening of adverse events, premature treatment discontinuations or switch due to toxicity within the first 6 months. Conclusions: In this large prospective study, we quantified the impact of PG on TAM PK and AAS, previously shown to predict RFS. Although the toxicity observed after 6 months of TAM does not seem correlated with PK or PG, these relationships need to be re-evaluated during the 3-year follow-up. Citation Format: White-Koning M, Arellano C, Le Morvan V, Evrard A, Puzskiel A, Vachoux C, Dauba J, Houyau P, Poublanc M, Robert J, Boyer J-C, Roché H, Thomas F, Chatelut E. Impact of genetic polymorphisms on plasma levels of tamoxifen and its metabolites and toxicity: 6-months results of the adjuvant breast cancer longitudinal PHACS study (NCT01127295) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-12-03.

Cytochrome P450 Genetic Variation Associated with Tamoxifen Biotransformation in American Indian and Alaska Native People.

Despite evidence that pharmacogenetics can improve tamoxifen pharmacotherapy, there are few studies with American Indian and Alaska Native (AIAN) people. We examined variation in cytochrome P450 (CYP) genes (CYP2D6, CYP3A4, CYP3A5, and CYP2C9) and tamoxifen biotransformation in AIAN patients with breast cancer (n = 42) from the Southcentral Foundation in Alaska and the Confederated Salish and Kootenai Tribes in Montana. We tested for associations between CYP diplotypes and plasma concentrations of tamoxifen and metabolites. Only the CYP2D6 variation was significantly associated with concentrations of endoxifen (P = 0.0008) and 4‐hydroxytamoxifen (P = 0.0074), tamoxifen's principal active metabolites, as well as key metabolic ratios. The CYP2D6 was also the most significant predictor of active metabolites and metabolic ratios in a multivariate regression model, including all four genes as predictors, with minor roles for other CYP genes. In AIAN populations, CYP2D6 is the largest contributor to tamoxifen bioactivation, illustrating the importance of validating pharmacogenetic testing for therapy optimization in an understudied population.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2D6 and Tamoxifen Therapy.

Tamoxifen is biotransformed by CYP2D6 to 4-hydroxytamoxifen and 4-hydroxy N-desmethyl tamoxifen (endoxifen), both with greater antiestrogenic potency than the parent drug. Patients with certain CYP2D6 genetic polymorphisms and patients who receive strong CYP2D6 inhibitors exhibit lower endoxifen concentrations and a higher risk of disease recurrence in some studies of tamoxifen adjuvant therapy of early breast cancer. We summarize evidence from the literature and provide therapeutic recommendations for tamoxifen based on CYP2D6 genotype.

Comprehensive assessment of cytochromes P450 and transporter genetics with endoxifen concentration during tamoxifen treatment.

Tamoxifen bioactivation to endoxifen is mediated primarily by CYP2D6; however, considerable variability remains unexplained. Our aim was to perform a comprehensive assessment of the effect of genetic variation in tamoxifen-relevant enzymes and transporters on steady-state endoxifen concentrations. Comprehensive genotyping of CYP enzymes and transporters was performed using the iPLEX ADME PGx Pro Panel in 302 tamoxifen-treated breast cancer patients. Predicted activity phenotype for 19 enzymes and transporters were analyzed for univariate association with endoxifen concentration, and then adjusted for CYP2D6 and clinical covariates. In univariate analysis, higher activity of CYP2C8 (regression β=0.22, P=0.020) and CYP2C9 (β=0.20, P=0.04), lower body weight (β=-0.014, P<0.0001), and endoxifen measurement during winter (each β<-0.39, P=0.002) were associated with higher endoxifen concentrations. After adjustment for the CYP2D6 diplotype, weight, and season, CYP2C9 remained significantly associated with higher concentrations (P=0.02), but only increased the overall model R by 1.3%. Our results further support a minor contribution of CYP2C9 genetic variability toward steady-state endoxifen concentrations. Integration of clinician and genetic variables into individualized tamoxifen dosing algorithms would marginally improve their accuracy and potentially enhance tamoxifen treatment outcomes.

Variations in plasma concentrations of tamoxifen metabolites and the effects of genetic polymorphisms on tamoxifen metabolism in Korean patients with breast cancer.

Inter-individual variation in tamoxifen metabolism in breast cancer patients is caused by various genetic and clinical factors. We measured the plasma concentrations of tamoxifen and its metabolites and investigated genetic polymorphisms influencing those concentrations. We measured the concentrations of tamoxifen, endoxifen, N-desmethyltamoxifen (NDM), and 4-hydroxytamoxifen (4-OH tamoxifen) in 550 plasma specimens from 281 breast cancer patients treated with tamoxifen. Duplicate or triplicate specimens were obtained from 179 patients at 3-month intervals. In 80 patients, genotyping for tamoxifen metabolizing enzymes was performed using the DMET Plus array and long-range PCR. Plasma concentrations of tamoxifen and its metabolites showed wide variations among patients. The following genetic polymorphisms were associated with the plasma concentrations when body mass index and tamoxifen concentrations were considered as co-variables: CYP1A2 -2467delT, CYP2B6 genotype, CYP2D6 activity score (AS), and FMO3 441C>T. CYP2D6 AS and three variants in the SULT1E1 gene showed correlation with ratios of tamoxifen metabolites. CYP2D6 AS was the only variable that showed associations with both metabolite concentration and ratio: endoxifen (P < 0.001), NDM (P < 0.001), endoxifen/NDM (P < 0.001), NDM/tamoxifen (P < 0.001), and 4-OH tamoxifen/tamoxifen (P = 0.005). Serial measurements of 448 plasma concentrations in 179 patients at 3-month intervals showed wide intra-individual variation. Our study showed that genetic polymorphisms can in part determine the baseline concentrations of tamoxifen and its metabolites. However, marked intra-individual variations during follow-up monitoring were observed, and this could not be explained by genotype. Therefore, serial measurements of tamoxifen and its metabolites would be helpful in monitoring in vivo tamoxifen metabolic status.

Improved Prediction of Endoxifen Metabolism by CYP2D6 Genotype in Breast Cancer Patients Treated with Tamoxifen.

Purpose: Prediction of impaired tamoxifen (TAM) to endoxifen metabolism may be relevant to improve breast cancer treatment, e.g., via TAM dose increase. The polymorphic cytochrome P450 2D6 (CYP2D6) strongly determines an individual’s capacity for endoxifen formation, however, CYP2D6 phenotype assignments inferred from genotype widely differ between studies. Thus, we modeled plasma endoxifen predictability depending on variable CYP2D6 genotype groupings.Methods: CYP2D6 diplotype and metabolite plasma concentrations were assessed in 908 pre- and post-menopausal estrogen receptor (ER)-positive, TAM treated early breast cancer patients of Caucasian (N = 678), Middle-Eastern Arab (N = 77), and Asian (N = 153) origin. Robust coefficients of determination (R2) were estimated for endoxifen (E) or metabolic ratio endoxifen/desmethyl-TAM (E/DMT) as dependent and different CYP2D6 phenotype assignments as independent variables. Allele activity scores (ASs) were modified with respect to a reduced ∗10 allele activity. Predictability of endoxifen plasma concentrations above the clinical threshold of 5.9 ng/mL was investigated by receiver operating characteristic (ROC) analysis.Results: CYP2D6 diplotypes (N = 898) were strongly associated with E and E/DMT independent of age (P < 10-15). Across all ethnicities, 68–82% inter-patient variability of E/DMT was explained by CYP2D6 diplotype, while plasma endoxifen was predictable by 39–58%. The previously used codeine specific phenotype classification showed worse prediction for both endpoints particularly in Asians (median R2< 20%; P < 10-9). Downgrading of ∗10 activity slightly improved the explanatory value of metabolizer phenotype (P < 0.002). Endoxifen plasma concentrations above the clinical threshold of 5.9 ng/mL were achieved in 82.3% of patients and were predictable (96% sensitivity, 57% specificity) by CYP2D6 diplotypes with AS > 0.5, i.e., omitting PM/PM and PM/IM patients.Conclusion: The CYP2D6 explanatory power for active drug level assessment is maximized by TAM-specific phenotype assignments while a genotype cutoff that separates PM/PM and PM/IM from the remaining patients may improve clinical benefit via increased endoxifen concentrations.

Impact of CYP2D6 polymorphisms on endoxifen concentrations and breast cancer outcomes.

We investigated the impact of germline CYP2D6 genotyping done using the non-tumor specimen on endoxifen concentrations and/or clinical outcomes in breast cancer (BC) patients treated with tamoxifen in published studies. We evaluated published data from 13 001 patients in 29 studies. Mean±s.d. endoxifen concentrations were significantly lower in poor metabolizers (PM) versus extensive metabolizers (EM) (8.8±7.2 versus 22.3±11.8 ng ml-1; P<0.05). The PM status did not influence clinical outcomes in majority of the studies. However, only one study followed the Gaedigk activity scoring for phenotypic assignments, which predicted recurrence-free survival in CYP2D6 poor metabolizers. In two independent studies with 1676 patients, low endoxifen concentrations predicted poor BC-free survival. From our review of published data we found that standardization of CYP2D6 genotype-phenotype classification is needed in order to ensure effective evaluation of associations between CYP2D6 polymorphisms and endoxifen concentrations and BC outcomes. Universal implementation of this standardization classification system should be a priority among researchers and laboratories. Furthermore, additional clinical research is warranted to determine whether patients with CYP2D6 PM phenotypes or low endoxifen levels will have better clinical outcomes with increased tamoxifen dosing compared to standard dosing.

Abstract 5033: Optimized CYP2D6 phenotype assignment for plasma endoxifen prediction in breast cancer patients treated with tamoxifen

Abstract Tamoxifen (Tam), a standard therapy for estrogen receptor (ER)-positive breast cancer, is bioactivated to its active metabolite endoxifen by the cytochrome P450 enzyme CYP2D6. CYP2D6 polymorphisms constituting extensive (EM), intermediate (IM) and poor (PM) metabolizer phenotypes are main determinants of variable endoxifen plasma concentrations and supposed to influence therapeutic efficacy. Genotype-guided prediction of TAM metabolizer status has long been debated to be useful for clinical dose adjustment in patients with impaired metabolism. As this requires accurate genotype-phenotype assignments, we tested several CYP2D6 phenotype classifications including the codeine metabolism-based scoring implemented by the ‘Clinical Pharmacogenetics Implementation Consortium’ (Crews et al. 2014, CPT) for their predictive value of active metabolite concentrations. We applied linear modelling of square-root transformed plasma endoxifen or log-transformed metabolic ratio (MR) endoxifen/desmethyl-TAM depending on CYP2D6 phenotype classification in a cohort of 936 pre- and postmenopausal TAM treated breast cancer patients of European, Middle Eastern Arabic, and Asian descent (Muerdter et al CPT 2011; Saladores et al. TPJ 2015). CYP2D6 diplotypes were defined by PM (*3, *4, *5, *6, *7), IM (*9, *10, *41), EM (*1, *2, *35) or UM (duplicated EM) alleles. CYP2D6 phenotypes were defined by various diplotype groupings and an adapted activity score regarding the *10 allele. Models were adjusted for CYP2C9 and CYP3A5 genotypes, and robust coefficients of determination (R2) with 95% confidence intervals from 10.000 bootstrap replicates were calculated using R package lmrob. Our analyses indicate, that the commonly used codeine-based CYP2D6 phenotype assignment poorly predicts CYP2D6 mediated endoxifen formation. This is evident from a low predictability (&amp;lt;20%) for both metabolite endpoints particularly in Asians, most likely due to a misclassification of abundant IM/IM (*10) diplotypes as EM. Importantly, the active metabolite-to-precursor MR appears to be the endpoint that is more closely linked to CYP2D6 enzyme activity, as it explains up to 68-82% of MR variability. In contrast, absolute endoxifen concentrations were only modestly predictable (38-57%) by CYP2D6 diplotype or other phenotype groupings. Moreover, a reduced activity for the *10 compared to other IM alleles appears to improve endoxifen predictabilty by phenotype. Personalized TAM treatment decisions based on plasma endoxifen prediction should rely on TAM specific CYP2D6 genotype-guided phenotype assignments that quantitatively capture the allele-dosage effects and that include endoxifen-to-precursor MR as the endpoint most directly linked to CYP2D6. Citation Format: Werner Schroth, Stefan Winter, Michel Eichelbaum, Thomas Muerdter, Matthias Schwab, Hiltrud Brauch. Optimized CYP2D6 phenotype assignment for plasma endoxifen prediction in breast cancer patients treated with tamoxifen [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5033. doi:10.1158/1538-7445.AM2017-5033

Abstract P2-09-11: Metabolite-guided long-term prediction of outcome in tamoxifen treated breast cancer patients

Abstract Background The genetic polymorphisms of CYP2D6 determine its enzymatic activity thereby the pharmacokinetic velocity by which tamoxifen (tam) is converted into active metabolites. Combined analyses of tam metabolites compared to CYP2D6 type and long-term survival could allow prediction of tam response and personalization of therapies. The clinical importance of defining such subgroups in the era of the new long-term (10-year) tam treatment paradigm is actualized. Material and Methods From May 1995 to December 1998, patients were included in an observational micro-metastasis study in the Oslo region and treated according to the national guidelines at the time (1). Serum samples were drawn at 3-year follow-up from 356 relapse-free patients, 106 of these were treated with tamoxifen. The median follow up time for breast cancer death was 16.8 years (3.5-19.4). Serum samples were processed using protein precipitation with acetonitrile. An Aquity UPLC system was used to chromatographically separate 10 tam metabolites using a BEH C18 Phenyl column (100 x 2.1 mm, 1.7 μm particle size) that was developed with a water-methanol gradient containing 0.1% formic acid. The LC system was coupled to a Xevo TQ-S tandem mass spectrometer equipped with an atmospheric pressure photoionization source. The method was validated with respect to linearity, imprecision, accuracy, and functional sensitivity according to FDA guidelines. Results The new LC-MS/MS method separated the active Z-isomers of 4OHtam and 4OHNDtam (endoxifen) from its inactive Z'-isomers and E-isomers. Imprecision (intra and inter-day CV %) was within 10 % for target concentrations for all metabolites and accuracies were in the range 95-106%. The method was validated with serum samples from 42 breast cancer patients using 20 mg of tamoxifen. The endoxifen concentrations ranged from 0 to 90 nM, with a median value of 25 nM. The previous observed endoxifen level of 10 nM in poor metabolizers (2) was used as cut-off for the grouping of patients. The nil endoxifen (NE) group (&amp;lt; 0.1nM, n=14) or low-endoxifene (LE) group (0.1-10 nM, n=8) were grouped together. Univariate survival analysis did not show a significant association between breast cancer specific survival and endoxifen levels. (p=0.15; logrank and p=0.18;Breslow). However, for the period beyond 10-years of follow-up the breast cancer survival differed between the high endoxifene (HE) group and the NE+LE groups. For patients surviving the first 10 years the breast cancer specific survival was 94.2% vs. 77.8% for the HE and NE+LE groups respectively (p=0.020, logrank and p=0.017, Breslow, HR=4.5, CI 95=1.1-17.9). In the multivariate analysis endoxifen ≤/&amp;gt; 10 nM remained the only factor in the final model. Discussion We developed a new accurate and precise LC-MS/MS method for the measurement of 10 tamoxifen metabolites. Importantly, the method separates active and inactive isomers of 4OHtam and 4OHNDtam/endoxifen. Despite the low number of patients, we observed a poorer long-term survival beyond 10 years in patients with nil or low serum concentration of endoxifen. A comprehensive analysis is presented addressing the relationship between genotyped based and metabolite based prediction of long-term outcome in tamoxifen treated breast cancer patients. Ref: 1. Wiedswang G, et al. Clin Ca Res; 2004 2. Mürdter TE, et al. Clin Pharmacol Ther; 2011. Citation Format: Helland T, Henne N, Bifulco E, Hustad SS, Kristensen VN, Lash T, Borgen E, Janssen EAM, Lien EA, Naume B, Mellgren G, Søiland H. Metabolite-guided long-term prediction of outcome in tamoxifen treated breast cancer patients [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-09-11.

Comprehensive assessment of cytochromes P450 and transporter genetics with endoxifen concentration during tamoxifen treatment

Comprehensive assessment of cytochromes P450 and transporter genetics with endoxifen concentration during tamoxifen treatment

An Antiestrogenic Activity Score for tamoxifen and its metabolites is associated with breast cancer outcome.

Endoxifen concentrations have been associated with breast cancer recurrence in tamoxifen-treated patients. However, tamoxifen itself and other metabolites also show antiestrogenic anti-tumor activity. Therefore, the aim of this study was to develop a comprehensive Antiestrogenic Activity Score (AAS), which accounts for concentration and antiestrogenic activity of tamoxifen and three metabolites. An association between the AAS and recurrence-free survival was investigated and compared to a previously published threshold for endoxifen concentrations of 5.97ng/mL. The antiestrogenic activities of tamoxifen, (Z)-endoxifen, (Z)-4-hydroxytamoxifen, and N-desmethyltamoxifen were determined in a cell proliferation assay. The AAS was determined by calculating the sum of each metabolite concentration multiplied by an IC50 ratio, relative to tamoxifen. The AAS was calculated for 1370 patients with estrogen receptor alpha (ERα)-positive breast cancer. An association between AAS and recurrence was investigated using Cox regression and compared with the 5.97ng/mL endoxifen threshold using concordance indices. An AAS thresholdof 1798 was associated with recurrence-free survival, hazard ratio (HR) 0.67 (95% confidence interval (CI) 0.47-0.96), bias corrected after bootstrap HR 0.69 (95% CI 0.48-0.99). The concordance indices for AAS and endoxifen did not significantly differ; however, using the AAS threshold instead of endoxifen led to different dose recommendations for 5.2% of the patients. Endoxifen concentrations can serve as a proxy for the antiestrogenic effect of tamoxifen and metabolites. However, for the aggregate effect of tamoxifen and three metabolites, defined by an integrative algorithm, a trend towards improving treatment is seen and moreover, is significantly associated with breast cancer recurrence.

Cytochrome P-450 2D6 (CYP2D6) Genotype and Breast Cancer Recurrence in Tamoxifen-Treated Patients: Evaluating the Importance of Loss of Heterozygosity.

Tamoxifen therapy for estrogen receptor-positive breast cancer reduces the risk of recurrence by approximately one-half. Cytochrome P-450 2D6, encoded by the polymorphic cytochrome P-450 2D6 gene (CYP2D6), oxidizes tamoxifen to its most active metabolites. Steady-state concentrations of endoxifen (4-hydroxy-N-desmethyltamoxifen), the most potent antiestrogenic metabolite, are reduced in women whose CYP2D6 genotypes confer poor enzyme function. Thirty-one studies of the association of CYP2D6 genotype with breast cancer survival have yielded heterogeneous results. Some influential studies genotyped DNA from tumor-infiltrated tissues, and their results may have been susceptible to germline genotype misclassification from loss of heterozygosity at the CYP2D6 locus. We systematically reviewed 6 studies of concordance between genotypes obtained from paired nonneoplastic and breast tumor-infiltrated tissues, all of which showed excellent CYP2D6 genotype agreement. We applied these concordance data to a quantitative bias analysis of the subset of the 31 studies that were based on genotypes from tumor-infiltrated tissue to examine whether genotyping errors substantially biased estimates of association. The bias analysis showed negligible bias by discordant genotypes. Summary estimates of association, with or without bias adjustment, indicated no clinically important association between CYP2D6 genotype and breast cancer survival in tamoxifen-treated women.