Potent CYP2D6 Inhibiting drugs do not increase relapse rate in early breast cancer patients treated with adjuvant tamoxifen

Time to Update Evidence-Based Guideline Recommendations About Concurrent Tamoxifen and Antidepressant Use? A Systematic Review

Concerns around pharmacological interaction between tamoxifen and antidepressants have resulted in evidence-base guidelines that recommend avoidance or caution with concurrent use. It remains unclear however whether this interaction is clinically important. A systematic review of studies comparing endocrine therapy (including tamoxifen and aromatase inhibitors) alone or concurrent with antidepressants in breast cancer patients was performed. The literature search sought studies within MEDLINE, EMBASE, and the Cochrane Collaboration Library published from database inception until December 1, 2020. Outcomes of interest included recurrence, breast cancer-specific survival, overall mortality, quality of life, and treatment compliance. Studies were assessed with the Cochrane Risk of Bias tool for randomized controlled trials and the Newcastle Ottawa tool for case-control and cohort studies. From 695 citations, we included 15 studies (2 randomized controlled trials [255 patients], 10 retrospective cohort studies [75,678 patients], and 3 case-control studies [18,836 patients]). While between-study clinical and methodologic differences (including analysis of confounding variables) precluded formal meta-analysis, findings from included studies did not find consistent evidence that concurrent use of antidepressants (including paroxetine) with tamoxifen therapy has negative impacts on the outcomes of interest. In this systematic review, despite data from nearly 100,000 patients, concurrent use of tamoxifen and antidepressants showed no consistent negative effect on clinical outcomes. Given the recognized harm to patients of changing either endocrine therapy or antidepressants to avoid concurrent use, current evidence-based guidelines should be updated accordingly. More rigorously designed pharmacoepidemiologic studies are needed.

Effect of selective serotonin reuptake inhibitors use on endocrine therapy adherence and breast cancer mortality: a population-based study

The purpose of the study was to investigate whether the concomitant use of selective serotonin reuptake inhibitors (SSRI) with tamoxifen influences the risk of death due to breast cancer, and we also investigated the association between SSRI use and adherence to oral endocrine therapy (ET). We analyzed data from BCBaSe Sweden, which is a database created by the data linkage of Registries from three different regions of Sweden. To investigate the association between ET adherence and SSRI use, we included all women who were diagnosed with non-distant metastatic ER-positive invasive breast cancer from July 2007 to July 2011 and had at least one dispensed prescription of oral tamoxifen or aromatase inhibitor. To investigate the role of concurrent administration of SSRI and tamoxifen on breast cancer prognosis, we performed a nested case–control study. In the adherence cohort, 9104 women were included in the analyses. Women who received SSRI, either before or after breast cancer diagnosis, were at higher risk for low adherence to ET. However, when the overlapping period between SSRI use and ET was >50 %, no excess risk for low adherence was observed. Non-adherence (<80 %) to ET was significantly associated with worse breast cancer survival (OR 4.07; 95 % CI 3.27–5.06). In the case–control study, 445 cases and 11125 controls were included. The concomitant administration of SSRI and tamoxifen did not influence breast cancer survival, neither in short-term (OR 1.41; 95 % CI 0.74–2.68) nor in long-term SSRI users (OR 0.85; 95 % CI 0.35–2.08). Concomitant SSRI and tamoxifen use does not seem to increase risk for death due to breast cancer. Given the positive association between continuing antidepressive pharmacotherapy for a longer period of time and adherence to ET, it is essential to capture and treat depression in breast cancer patients to secure adherence to ET.

Breast cancer recurrence in relation to antidepressant use

PURPOSE

Women with breast cancer frequently use antidepressants; however, questions about the effect of these medications on breast cancer recurrence remain.

METHODS

We identified 4,216 women ≥18 years with an incident stage I or II breast cancer diagnosed between 1990 and 2008 in a mixed-model healthcare delivery system linked to a cancer registry. Recurrences were ascertained from chart review. Medication exposures were extracted from electronic pharmacy records. We used multivariable Cox proportional hazards models to estimate hazard ratios (HR) and 95 % confidence intervals (CI) to assess the association between antidepressant use and breast cancer recurrence and mortality. We also conducted analyses restricted to tamoxifen users.

RESULTS

Antidepressants overall, tricyclic antidepressants, and selective serotonin reuptake inhibitors were not associated with risk of breast cancer recurrence or mortality. Women taking paroxetine only (adjusted HR: 1.66; 95 % CI 1.02, 2.71) and trazodone only (adjusted HR: 1.76; 95 % CI 1.06, 2.92), but not fluoxetine only (adjusted HR: 0.92; 95 % CI 0.55, 1.53), had higher recurrence risks than antidepressant nonusers. There was some suggestion of an increased recurrence risk with concurrent paroxetine and tamoxifen use compared with users of tamoxifen only (adjusted HR: 1.49; 95 % CI 0.79, 2.83).

CONCLUSIONS

In general, antidepressants did not appear increase risk of breast cancer recurrence, though there were some suggested increases in risk that warrant further investigation in other datasets. Our results combined systematically and quantitatively with results from other studies may be useful for patients and providers making decisions about antidepressant use after breast cancer diagnosis.

Pharmacogenomics toward personalized tamoxifen therapy for breast cancer

Tamoxifen has been used not only for the treatment or prevention of recurrence in patients with estrogen receptor positive breast cancers but also for recurrent breast cancer. Because CYP2D6 is known to be an important enzyme responsible for the generation of the potent tamoxifen metabolite, ‘endoxifen’, lots of studies reported that genetic variation which reduced its enzyme activity were associated with poor clinical outcome of breast cancer patients treated with tamoxifen. However, there are some discrepant reports questioning the association between CYP2D6 genotype and clinical outcome after tamoxifen therapy. Dose-adjustment study of tamoxifen based on CYP2D6 genotypes provides the evidence that dose adjustment is useful for the patients carrying reduced or null allele of CYP2D6 to maintain the effective endoxifen level. This review describes critical issues in pharmacogenomic studies as well as summarizes the results of the association of CYP2D6 genotype with tamoxifen efficacy.

How often did Belgian physicians co-prescribe tamoxifen with strong CYP2D6 inhibitors over the last 6 years?

AIMS

Tamoxifen is widely used in the treatment of breast cancer. It is a pro-drug metabolized to the more active endoxifen through CYP2D6. Concomitant intake of CYP2D6 inhibitors results in lower endoxifen levels and could influence efficacy. The objective of this study was to evaluate the evolution of co-prescription of tamoxifen and CYP2D6 inhibitors in Belgium.

METHODS

Data were retrieved from the Pharmanet database of the National Institute for Health and Disability Insurance for the period January 2006-December 2009. For the analysis of the evolution of the co-prescription, the period was divided in subperiods of 2 months. The category tamoxifen+CYP2D6 inhibitor was defined as women who were delivered tamoxifen and a CYP2D6 inhibitor in that subperiod. The results were validated on the period December 2011-May 2012.

RESULTS

The percentage of co-prescription decreased over time for the strong CYP2D6 inhibitors and increased for the weak CYP2D6 inhibitor, with these trends persisting in 2012. Tamoxifen and CYP2D6 inhibitors were mostly prescribed by general practitioners and gynaecologists and by general practitioners and psychiatrists, respectively.

DISCUSSION

This study shows that a proportion of women taking tamoxifen in Belgium are prescribed a strong CYP2D6 inhibitor, which could affect tamoxifen efficacy. Over time, the concomitant intake decreased. Paroxetine was the most prescribed strong CYP2D6 inhibitor. Venlafaxine, a weak CYP2D6 inhibitor, was prescribed more often. This study also shows that tamoxifen and the CYP2D6 inhibitors are not only prescribed by physicians specialized in breast cancer; therefore, all physicians should be aware of this interaction.

Metabolism and transport of tamoxifen in relation to its effectiveness: new perspectives on an ongoing controversy

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.

CYP2D6 polymorphisms influence tamoxifen treatment outcomes in breast cancer patients: a meta-analysis

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.

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

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.

CYP2D6 phenotype indicative for optimized antiestrogen efficacy associates with outcome in early breast cancer patients

BACKGROUND

Endoxifen serum concentrations seem to correlate with outcome in breast cancer (BC) patients. Concurrently, cytochrome P450 2D6 (CYP2D6) enzyme activity and dextromethorphan (DM) metabolism are deemed a surrogate marker for the formation of endoxifen. Here, we conducted a matched cohort study to determine the impact of an extensive CYP2D6 phenotype on relapse in patients with early-stage estrogen receptor (ER)-positive BC and adjuvant tamoxifen intake.

METHODS

CYP2D6 extensive metabolism was determined upon appropriate dextromethorphan/dextrorphan (DM/DX) urinary excretion ratios (≤0.30). Fifty-nine BC patients were identified as extensive phenotype metabolizers, while for 148 matched controls, CYP2D6 was not determined. Patients and controls did not differ with respect to age, stage, hormone receptor status, HER2, grade, menopausal status, chemotherapy and antihormonal therapy. Survival analysis was performed according to clinical follow-up.

RESULTS

Disease-free survival (DFS) of patients identified as extensive CYP2D6 metabolizers did not differ significantly from controls (p = 0.10). However, when patients with ER expression of ≤ 20 % were excluded from the analysis, DFS was associated with a more favorable outcome (p = 0.06).

CONCLUSIONS

This study suggests a positive association between extensive CYP2D6 metabolism and outcome in early-stage ER-positive BC patients using tamoxifen and in particular, when a sufficient number ERs are represented on the primary tumor.

Impact of CYP2D6 polymorphism on tamoxifen therapy: where are we?

Tamoxifen is a mainstay in the treatment of hormone-receptor sensitive breast cancer. To be effective, it needs conversion into 4-hydroxy-tamoxifen and endoxifen. The key enzyme involved is encoded by the gene CYP2D6 of which several, sometimes population-specific alleles are known. Corresponding enzyme variants may result in poor, intermediate, and extensive metabolization and therefore different steady-state plasma levels of active metabolites. Those are hypothesized to be linked to clinical outcomes of tamoxifen therapy. However, a wealth of mostly retrospective cohort studies came up with conflicting results. Appraisal of these studies is difficult and a metaanalysis impossible due to heterogeneity of patient populations, disease factors, treatment modalities, and measured outcomes. As standardization would not overcome intrinsic limitations of retrospective analyses, prospective trials comparing genotype-guided versus unsighted tamoxifen treatment are required to prove whether routine CYP2D6 genotyping is clinically effective and cost-effective.

Personalized participatory medicine: sharing knowledge and uncertainty

Informing patients about risks and benefits of alternative treatment options and choosing between them is becoming a bigger challenge as knowledge about the relationship between the individual's genetic profile and the efficacy and safety of available medications accumulates. Putting personalized medicine into practice requires new modes of information sharing and decision making by patient and physician. This is illustrated by a case study on treatment choices of breast cancer patients following genotyping for CYP2D6, recently published in Genome Medicine.

See research article: http://genomemedicine.com/content/3/10/64

Evaluation of CYP2D6 and efficacy of tamoxifen and raloxifene in women treated for breast cancer chemoprevention: results from the NSABP P1 and P2 clinical trials

BACKGROUND

Controversy exists regarding the association between CYP2D6 enzyme activity and tamoxifen effectiveness in the adjuvant treatment of invasive breast cancer; however, this association in the primary prevention of breast cancer is unknown.

METHODS

We conducted a nested case-control study in the context of the NSABP P1 and P2 prevention trials to determine the impact of CYP2D6 genotype, CYP2D6 inhibitor use, and metabolizer status (CYP2D6 genotype combined with CYP2D6 inhibitor use), on breast cancer events. Women who developed breast cancer (both noninvasive and invasive) while on 5 years of selective estrogen receptor modulators therapy (cases) were matched to controls free of breast cancer. Comprehensive CYP2D6 genotyping was conducted for alleles associated with absent (*3, *4, *5, and *6), reduced (*10, *17, and *41), and increased (*1XN and *2XN) enzyme activity. Information regarding the use of CYP2D6 inhibitors was recorded.

RESULTS

A total of 591 cases were matched to 1,126 controls and DNA was genotyped in more than 97%. In patients treated with tamoxifen, there was no association of CYP2D6 genotype [OR (extensive/poor metabolizer): 0.90; 95% CI: 0.46-1.74, P = 0.74), use of a potent CYP2D6 inhibitor (OR 0.92; 95% CI: 0.575-1.486), or CYP2D6 metabolizer status (OR 1.03; 95% CI: 0.669-1.607) with breast cancer occurrence. Likewise, there was no association between any CYP2D6 metabolism parameter with breast cancer events in raloxifene-treated patients.

CONCLUSION

In the NSABP P1 and P2 clinical trials, alterations in CYP2D6 metabolism are not associated with either tamoxifen or raloxifene efficacy.

Clinical epidemiology and pharmacology of CYP2D6 inhibition related to breast cancer outcomes

Adjuvant tamoxifen therapy of breast cancer patients with estrogen receptor-positive tumors reduces the rate of breast cancer recurrence by approximately a half. Tamoxifen is metabolized by several polymorphic enzymes, including cytochrome P450 2D6 (CYP2D6), to more active metabolites. We have reviewed the clinical pharmacology of tamoxifen and evaluated the evidence from clinical epidemiology studies regarding the association between CYP2D6 inhibition and tamoxifen effectiveness. We conclude that the impact of CYP2D6 inhibition on tamoxifen effectiveness is likely to be null or small, at least in the populations studied so far. Understanding the effect of variations in tamoxifen metabolism on breast cancer outcomes, if any, will likely require a broader perspective, including examination of the complete metabolic pathway and subgroups of patients with other markers of potentially poor tamoxifen response.