Vincent O. Dezentjé

Effect of Concomitant CYP2D6 Inhibitor Use and Tamoxifen Adherence on Breast Cancer Recurrence in Early-Stage Breast Cancer

PURPOSE The use of cytochrome P450 2D6-inhibiting drugs (CYP2D6 inhibitors) during tamoxifen treatment leads to a decrease in plasma concentration of endoxifen, the major active tamoxifen metabolite. Concomitant use of CYP2D6 inhibitors, such as selective serotonin reuptake inhibitors, as well as low tamoxifen adherence may negatively impact tamoxifen efficacy in patients with breast cancer. The objectives of this study were to relate concomitant CYP2D6 inhibitor use and tamoxifen adherence to breast cancer event-free time (EFT). PATIENTS AND METHODS Data were from PHARMO and included a community pharmacy dispensing database; PALGA, a nationwide pathology database; and the Dutch Medical Register in the Netherlands. Patients with breast cancer treated with adjuvant tamoxifen between 1994 and 2006 were included. A Cox proportional hazards model with a time-dependent definition for concomitant CYP2D6 inhibitor exposure was used. Adherence calculated over the first year after tamoxifen initiation was related to breast cancer events in the following period. RESULTS In total, 1,962 patients with breast cancer using tamoxifen were included, among whom 150 (7.6%) frequently used a CYP2D6 inhibitor during tamoxifen treatment. No association between concomitant CYP2D6 inhibitor use and breast cancer recurrence was observed (adjusted hazard ratio [HR], 0.87; 95% CI, 0.42 to 1.79; P = .69). Poor tamoxifen adherence was associated with lower EFT (adjusted HR, 0.987; 95% CI, 0.975 to 0.999; P = .029). CONCLUSION This observational study did not show an association between concomitant CYP2D6 inhibitor use and breast cancer recurrence among patients treated with adjuvant tamoxifen despite the strong biologic rationale. This study shows, to the best of our knowledge for the first time, that poor tamoxifen adherence is associated with an increased risk of breast cancer events.

Clinical Implications of CYP2D6 Genotyping in Tamoxifen Treatment for Breast Cancer

In October 2006 the Food and Drug Administration recommended an update in the tamoxifen label to reflect the increased risk of recurrence in breast cancer patients who are cytochrome P450 2D6 (CYP2D6) poor metabolizers. This recommendation was based on only a few studies at that time. More clinical studies addressing the relation between the CYP2D6 genotype and tamoxifen efficacy have been published since, mostly describing Caucasian populations in the adjuvant treatment setting. An updated analysis of the literature is presented. Furthermore, the possibility to implement CYP2D6 genotyping in clinical practice is evaluated by analyzing the results of six studies on mainly Caucasian patients using adjuvant tamoxifen. Three studies were consistent with the FDA advice, but the three other studies showed contradictory results. Although some of the published criticism on the negative studies is justified, this does not imply that these results should be discarded. The reviewed literature is put in perspective acknowledging the limiting effect of Mendelian randomization on confounding and the limitations of the various study designs. The current accumulation of data showing worse clinical outcome in patients with decreased CYP2D6 metabolism in other types of populations still indicates that the CYP2D6 genotype may well become a clinically relevant predictive marker. The CYP2D6 genotype might be one of the first predictors of therapeutic response in cancer care based on germline DNA creating the possibility to analyze blood instead of tumor.

Genotyping of DNA Samples Isolated from Formalin-Fixed Paraffin-Embedded Tissues Using Preamplification

DNA isolated from formalin-fixed paraffin-embedded (FFPE) tissue is often fragmented and cross-linked and is therefore difficult to genotype. To enable this source of DNA for genotyping analysis using Taqman probes, we tested whether enrichment of the target genes would increase the amount of available DNA. For enrichment of the target genes, we used preamplification by means of diluted Taqman assays. To establish the appropriateness of preamplification, we used DNA extracted from paraffin-embedded tissue and compared the genotyping results of a series of single nucleotide polymorphisms assessed in DNA samples with and without preamplification. In a subset of patients, DNA was isolated from both blood and FFPE tissue to test the reliability of genotyping results derived after preamplification. We found an increase in call rate after preamplification and a convincing concordance in genotype. Based on our findings, we can safely conclude that preamplification of DNA isolated from paraffin-embedded tissue is a valuable and reliable method to optimize genotyping results.

Concomitant CYP2D6 inhibitor use and tamoxifen adherence in early-stage breast cancer: A pharmacoepidemiologic study

CRA509 Background: The use of cytochrome P450 2D6 inhibiting drugs (CYP2D6 inhibitors) during tamoxifen treatment leads to a decrease in plasma concentration of endoxifen, the major active tamoxifen metabolite. Concomitant use of CYP2D6 inhibitors, such as the commonly prescribed selective serotonin reuptake inhibitors, as well as low tamoxifen adherence may negatively impact tamoxifen efficacy in breast cancer. The objectives were to relate concomitant CYP2D6 inhibitor use and tamoxifen adherence to breast cancer event free time (EFT). METHODS Data were used from PHARMO, a pharmacy database, PALGA, a nationwide pathology database and the Dutch Medical Register in the Netherlands. Breast cancer patients who were treated with tamoxifen as adjuvant therapy between 1994 and 2006 were included. A Cox proportional hazards model with a time-dependent definition for the CYP2D6 inhibitor exposure was used. RESULTS 1,990 breast cancer patients using tamoxifen were included, among whom 215 (10.8%) used a CYP2D6 inhibitor during tamoxifen treatment. No association between concomitant CYP2D6 inhibitor use and breast cancer recurrence was observed. Poor tamoxifen adherence was associated with lower EFT. CONCLUSIONS This observational study did not show an association between concomitant CYP2D6 inhibitor use and breast cancer recurrence among patients treated with adjuvant tamoxifen. However, this study shows for the first time that poor tamoxifen adherence is associated with lower EFT. No significant financial relationships to disclose.

The Effect of Tamoxifen Dose Increment in Patients With Impaired CYP2D6 Activity.

Background: The effect of tamoxifen dose elevation on endoxifen serum concentration was investigated in patients with reduced CYP2D6 activity resulting from genetic variation and/or CYP2D6 inhibitor use. Additionally, baseline differences in endoxifen concentrations between the different CYP2D6 phenotypes were studied. Methods: Patients, treated with tamoxifen 20 mg once daily (QD) for at least 4 weeks, were classified as phenotypic extensive (EM), intermediate (IM), or poor (PM) metabolizer based on their genotype and comedication. In patients with an IM or PM phenotype, the tamoxifen dose was increased to 40 mg QD for 4 weeks. Tamoxifen, 4-OH-tamoxifen, N-desmethyltamoxifen, and endoxifen serum concentrations were measured at baseline and 4 weeks after the dose increment. Side effects of tamoxifen were assessed using the validated Functional Assessment of Cancer Therapy–Endocrine Symptom subscale (FACT-ESS-19). Results: The median baseline endoxifen concentration differed between EMs (11.4 mcg/L: n = 19), IMs (8.3 mcg/L: n = 16), and PMs (4.0 mcg/L: n = 7), P = 0.040. Tamoxifen dose elevation significantly increased the median endoxifen concentrations in 12 IMs from 9.5 to 17.4 mcg/L (P < 0.001) and in 4 PMs from 3.8 to 7.8 mcg/L (P = 0.001), without influencing median FACT-ESS-19 scores. Conclusions: Raising the tamoxifen dose to 40 mg QD significantly increased endoxifen concentrations in IMs and PMs without increasing side effects. The tamoxifen dose increment in PMs was insufficient to reach endoxifen concentrations equal to those observed in EMs. Future studies will clarify the direct effect of endoxifen exposure on tamoxifen efficacy and may reveal a threshold endoxifen concentration that is critical for its efficacy.

The effect of rs5758550 on CYP2D6*2 phenotype and formation of endoxifen in breast cancer patients using tamoxifen

AIM CYP2D6*2 is considered fully active, but it has been suggested that it only happens in the presence of rs5758550. This study aims to elucidate the impact of this enhancer. MATERIALS & METHODS DNA and blood samples from women enrolled in the CYPTAM study (NTR1509) were analyzed. Fourteen CYP2D6*2 carriers without the enhancer were reclassified. The relationship of CYP2D6 phenotypes and drug levels was studied. RESULTS After correction for the absence of the enhancer, the correlation between CYP2D6 phenotypes and endoxifen did not improve (R2: 0.290 vs 0.279). No difference was observed in mean concentrations between CYP2D6*2 individuals with and without the enhancer. CONCLUSION The rs5758550 enhancer does not lead to improved prediction of endoxifen levels in breast cancer patients.

Sunitinib treatment in a patient with metastatic renal cell carcinoma and bariatric surgery

In the past decade, many tyrosine kinase inhibitors (TKI) were added to the arsenal of oral oncolytics used in the treatment of a variety of malignancies. In contrary to intravenous drugs, the bioavailability of orally administered drugs depends on gastrointestinal absorption and first-pass metabolism. Challenges in reaching effective plasma levels may arise in patients with altered gastrointestinal anatomy, while pharmacokinetics can differ. In this case report, we demonstrate a patient with a history of gastric bypass surgery due to obesity and an indication for treatment with sunitinib for metastatic renal cell carcinoma (mRCC). Since the plasma concentration of sunitinib and its active metabolite desethylsunitinib appeared to be inadequate during the standard treatment regimen, the sunitinib dose was successfully escalated.

Abstract P3-07-46: CYPTAM-BRUT 3: Endometrial thickness cannot be used as a marker for tamoxifen metabolization in postmenopausal breast cancer patients

Background: Tamoxifen is commonly used for the treatment of all stages of estrogen receptor (ER) positive breast cancer (BC), the largest group of BC. In postmenopausal women, known endometrial side-effects are cystic appearance, hyperplasia, polyps and endometrial cancer. Tamoxifen is converted through several CYP450 enzymes into the active metabolite endoxifen. Patients with particular single nucleotide polymorphisms (SNPs) in those CYP450 enzymes (e.g. CYP2D6) have lower endoxifen concentrations and therefore could experience less benefit from tamoxifen. However, the clinical significance stays controversial in the literature as results remain contradictory. Our primary hypothesis is that women with lower endoxifen levels do not have the typical tamoxifen-induced increase in endometrial thickness. The aim of this study is to test the association between endoxifen concentration and the increase in double endometrial thickness (DET). Patients and methods: CYPTAM-BRUT 3 is a prospective, multicentric study including postmenopausal women with an ER positive BC receiving tamoxifen in the adjuvant setting. Primary objective is the association between serum endoxifen levels and change in DET between baseline and follow-up after 3 - 6 months. Secondary objectives are investigating the relation between serum endoxifen levels and other endometrial changes (i.e. the presence of cysts/polyps), menopausal symptoms assessed with a questionnaire and serum levels of follicle-stimulating hormone (FSH) and sex hormone-binding globulin (SHBG). Other objectives are the association between the 9CYP2D6 tamoxifen activity score9, based on SNPs and co-medication, and DET, other endometrial changes, FSH and SHBG. The CYPTAM-BRUT 3 study is a sub-study of the CYPTAM study in Leiden, The Netherlands, with survival as primary outcome. Results: 144 women were included in 19 hospitals. There was no significant association found between endoxifen and change in DET (p=0.888), as for the association between endoxifen and the development of cysts or polyps (p=0.208). For the questionnaire items no correlation was found (p≥0.051). Changes of FSH and SHBG were in the range of what would be expected during tamoxifen treatment in the general population and there was no association with endoxifen (p=0.726 and p=0.181). In addition, no association was found between the CYP2D6 TAS score and DET (p=0.613), other endometrial changes (p=0.196), FSH (p=0.976) and SHBG (p=0.900). Conclusion: Our study is one of the first studies that prospectively investigated the relation between tamoxifen metabolization, in correlation with endometrial thickness and SNPs. We can conclude that the typical increase in endometrial thickness seen in a significant proportion of postmenopausal women under tamoxifen cannot be used to predict that those women have a high endoxifen concentration or that women without an increased endometrial thickness have a significantly lower endoxifen concentration. The same conclusions can be made for the other tamoxifen-induced changes as cysts and polyps, menopausal symptoms, FSH and SHBG. It may also apply to tamoxifen efficacy but further prospective studies looking at survival are needed to answer that question. Citation Format: Poppe A, Dieudonne A-S, Lintermans A, Laenen A, Blomme C, Lambrechts D, Wildiers H, Christiaens M-R, Timmerman D, Van Calster B, Vereecke C, Vandeputte G, Fontaine C, Decloedt J, Berteloot P, Depypere H, Joerger M, Dezentje V, Neven P. CYPTAM-BRUT 3: Endometrial thickness cannot be used as a marker for tamoxifen metabolization in postmenopausal breast cancer patients. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-07-46.

Abstract OT2-1-05: Prospective multicenter study evaluating the effect of impaired tamoxifen metabolization on efficacy in breast cancer patients receiving tamoxifen in the neo-adjuvant or metastatic setting - The CYPTAM-BRUT 2 trial

Background Tamoxifen is commonly used to treat and prevent hormone receptor positive breast cancers. This drug is metabolized into more active metabolites by liver enzymes such as cytochrome P450 (CYP) enzymes. Endoxifen is considered to be the principal active metabolite of tamoxifen. As CYP enzymes are highly polymorphic in humans, endoxifen plasma levels are modulated by the patient’s genotype. It, however, is not yet clear if lowered endoxifen plasma levels have an effect on tamoxifen efficacy. This is the first prospective study where the association between endoxifen plasma concentrations, multiple CYP-genotypes and clinical outcome in postmenopausal patients treated with tamoxifen is investigated. Trial Design CYPTAM-BRUT 2 is a prospective multi-center open label, single-arm, non-randomized observational study. Postmenopausal women with measurable, estrogen receptor positive breast cancer receiving tamoxifen as neo-adjuvant or as first-line metastatic treatment are included in this study. The objective treatment response and clinical benefit are observed to investigate the efficacy of 20 mg tamoxifen daily. Patients are allowed to have started tamoxifen before inclusion but not more than three months. Further, if more than twelve months have passed after completion of the adjuvant therapy prior endocrine therapy in the adjuvant setting is allowed. Patients receiving neo-adjuvant tamoxifen will be assessed no more than four months after starting with tamoxifen. The primary endpoint is a statistical association between steady-state endoxifen plasma concentrations and the objective response rate (ORR) after 3-6 months of tamoxifen, under the assumption that the relationship is linear with an odds ratio (OR) of 1.49 per 10 nmol/L. Using available data on endoxifen concentrations, this OR is chosen to reflect an improvement from 10% ORR in the lowest endoxifen quartile to 30% in the highest endoxifen quartile when the overall ORR is around 18%. To have 90% power at a 5% significance level, 180 patients have to be included into the study. The main secondary study endpoint is the relation between endoxifen plasma concentrations and clinical benefit (CR+PR+SD at 6 months). The study has to include 270 patients to detect a statistically significant association with endoxifen with 90% power at a 5% significance level, assuming an OR of 1.28 per 10 nmol/L. This OR is chosen to reflect an improvement of clinical benefit at 6 months from 30% in the lowest endoxifen quartile to 50% in the highest endoxifen quartile (overall clinical benefit around 39%). For both endpoints the RECIST criteria are used. Other endpoints are progression-free survival, tolerability of tamoxifen treatment and the association between CYP2D6 genotype and clinical outcome. Patient accrualPatients from 22 participating centers in Belgium and Switzerland are included in this trial. In May 2014, the predefined sample size of 270 patients was reached. Follow-up of the last patients will continue until all required data are obtained (i.e blood samples and response evaluation). Citation Format: Kathleen Van Asten, Lynn Jongen, Anne-Sophie Dieudonne, Anneleen Lintermans, Chantal Blomme, Olivier Brouckaert, Diether Lambrechts, Hans Wildiers, Marie-Rose Christiaens, Dirk Timmerman, Ben Van Calster, Jan Decloedt, Patrick Berteloot, Didier Verhoeven, Markus Joerger, Khalil Zaman, Vincent Dezentje, Patrick Neven. Prospective multicenter study evaluating the effect of impaired tamoxifen metabolization on efficacy in breast cancer patients receiving tamoxifen in the neo-adjuvant or metastatic setting - The CYPTAM-BRUT 2 trial [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr OT2-1-05.