Trends in co-prescribing of antidepressants and tamoxifen among women with breast cancer, 2004-2010

Overview of sexual dysfunction in patients with cancer

Among survivor's patients with cancer, sexual dysfunction (SD) is a common treatment-related disturbance that significantly affects their quality of life. The disorder can be a short-term effect, but frequently it can be permanent and patients often do not receive adequate support to overcome the problem. The characteristics of SD may differ depending on the type of neoplasm and oncological treatment. The most common long-term effects are those related to treatment-induced menopause, ablative oncologic surgery, and altered gonadal function. Breast, prostate, and gynecologic cancers are the tumors most commonly associated with disturbances in sexual health, although there is evidence of SD in patients with other types of neoplasms. It is necessary for the healthcare team caring for oncological patients to be aware of the characteristics of sexual dysfunction in this population. This will make it possible to offer patients a comprehensive and personalized approach to improve their quality of life.

The Role of the Pharmacist in Patient Self-Advocacy for Osteoporosis Screening

Background Osteoporosis is a common bone disease affecting more than 200 million people worldwide. Commonly prescribed medications have the potential to contribute to bone loss and fracture risk. Providers may be unaware of effects of other commonly used medication classes, which can lead to inadequate prevention or a lack of screening. Objective To describe a case of drug-induced bone density loss, characterized by long-term use of proton pump inhibitors (PPIs) in a postmenopausal woman; to describe the pharmacist’s role in encouraging patient self-advocacy. Setting A rural and medically underserved area in eastern Washington State. Practice Description This patient case was part of a grant-funded project to identify and intervene with complex and high-risk patients from local rural and underserved populations. Practice Innovation A pharmacist met with a 61-year-old female patient to complete a comprehensive medication review and subsequently identified a risk of osteoporosis secondary to long-term PPI and hormone replacement therapy use. Empowered by the knowledge of risk of development of low bone density, the patient approached her provider twice with a request for bone density measurement. Results Despite initial hesitancy from her physician, the patient advocated for herself with concerns about developing osteoporosis. Following obtaining a dual energy X-ray absorptiometry scan, the patient received a diagnosis of osteoporosis. Discussion Education from the pharmacist prompted the patient to advocate for osteoporosis screening and ultimately led to a diagnosis. Conclusion Pharmacists play a critical role in identifying medication-induced conditions in patients with complex medications and multiple chronic disease states.

Selective serotonin reuptake inhibitors associated with increased mortality risk in breast cancer patients in Northern Israel

BACKGROUND

Approximately one in six women in the USA takes antidepressants and a third use selective serotonin reuptake inhibitors (SSRIs) after breast cancer diagnosis. Recent investigation demonstrated serotonin receptor (5-HTR2B) expression in the breast and serotonin production as an indicator of poor breast cancer prognosis. This study investigates the association between SSRI use at different time intervals relative to breast cancer diagnosis on survival.

METHODS

A population-based sample of 6959 consecutive, newly diagnosed breast cancer cases in Northern Israel was included. Patients were recruited from January 2000 and followed up through March 2020. Participants completed risk factor questionnaires regarding medical, reproductive and family history, medication use and health habits. Full prescription data were available through the Israeli national Clalit medical database. Multivariate Cox proportional hazard models were used to determine survival based on time of SSRI use.

RESULTS

Use of SSRIs in the 5 years prior to breast cancer diagnosis was associated with a 66% increase in overall mortality (HRadj = 1.66; CI: 1.05-2.63). SSRI use that initiated after breast cancer diagnosis was associated with an 81% increase in mortality (HRadj = 1.81; CI: 1.58-2.06). Use of SSRIs in the 5 years post-diagnosis was associated with a dose-response increase (P < 0.001) in long-term mortality (>5 years). Heavy SSRI use (≥24 prescription fills) after diagnosis was associated with nearly doubling in mortality (HR = 1.99; CI: 1.39-2.83).

CONCLUSION

SSRI use prior to and after breast cancer diagnosis is associated with increased mortality in breast cancer patients. Additional research is needed to better understand mechanisms mediating this association.

Importance of medication reconciliation in cancer patients

Cancer patients are a complex and vulnerable population whose medication history is often extensive. Medication reconciliations in this population are especially essential, since medication discrepancies can lead to dire outcomes. This commentary aims to describe the significance of conducting medication reconciliations in this often-forgotten patient population. We discuss additional clinical interventions that can arise during this process as well. Medication reconciliations provide the opportunity to identify and prevent drug-drug and herb-drug interactions. They also provide an opportunity to appropriately adjust chemotherapy dosing according to renal and hepatic function. Finally, reconciling medications can also provide an opportunity to identify and deprescribe inappropriate medications. While clinical impact appears evident in this landscape, evidence of economic impact is lacking. As more cancer patients are prescribed a combination of oral chemotherapies, intravenous chemotherapies and non-anticancer medications, future studies should evaluate the advantages of conducting medication reconciliations in these patient populations across multiple care settings.

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.

Prevalence of the co-prescription of tamoxifen and CYP2D6 inhibitors in Saudi population: A cross sectional study

Consumption of Cytochrome P450 2D6 (CYP2D6) inhibiting drugs along with tamoxifen treatment results in decrease in plasma concentration of endoxifen, the major active tamoxifen metabolite. Simultaneous use of CYP2D6 inhibitors, such as selective serotonin reuptake inhibitors (SSIs), as well as lesser tamoxifen adherence may negatively impact tamoxifen efficacy in patients with breast cancer. The objective of our study was to assess the co-prescription of CYP2D6 inhibitors and tamoxifen use and also to relate concomitant CYP2D6 inhibitor use and tamoxifen adherence to breast cancer in Riyadh, Saudi Arabia. All patients treated for breast cancer who had at least one tamoxifen prescription in their electronic medical records (EMRs) from June 2015 to June 2017 were included. Patients who had other adjuvant hormonal therapy were excluded from the study. In total, 499 patients (25 males and 474 females) with breast cancer using tamoxifen were included. Our study was purely observational study revealed that prescription of weak inhibitors with tamoxifen increased in the second year as opposed to decrease in the prescription of strong inhibitors. Also, a substantial percentage of patient population were found to be non-adherent to the tamoxifen therapy in this study.

Risk of mortality with concomitant use of tamoxifen and selective serotonin reuptake inhibitors: multi-database cohort study

OBJECTIVE

 To compare differences in mortality between women concomitantly treated with tamoxifen and selective serotonin reuptake inhibitors (SSRIs) that are potent inhibitors of the cytochrome-P450 2D6 enzyme (CYP2D6) versus tamoxifen and other SSRIs.

DESIGN

 Population based cohort study.

SETTING

 Five US databases covering individuals enrolled in private and public health insurance programs from 1995 to 2013.

PARTICIPANTS

 Two cohorts of women who started taking tamoxifen. In cohort 1, women started taking an SSRI during tamoxifen treatment. In cohort 2, women were already taking an SSRI when they started taking tamoxifen.

MAIN OUTCOME MEASURES

 All cause mortality in each cohort in women taking SSRIs that are potent inhibitors of CYP2D6 (paroxetine, fluoxetine) versus other SSRIs. Propensity scores were used to match exposure groups in a variable ratio fashion. Results were measured separately for each cohort and combined hazard ratios calculated from Cox regression models across the two cohorts with random effects meta-analysis.

RESULTS

 There were 6067 and 8465 new users of tamoxifen in cohorts 1 and 2, respectively. Mean age was 55. A total of 991 and 1014 deaths occurred in cohorts 1 and 2 during a median follow-up of 2.2 (interquartile range 0.9-4.5) and 2.0 (0.8-3.9) years, respectively. The pooled hazard ratio for death for potent inhibitors (rate 58.6/1000 person years) compared with other SSRIs (rate 57.9/1000 person years) across cohorts 1 and 2 was 0.96 (95% confidence interval 0.88 to 1.06). Results were consistent across sensitivity analyses.

CONCLUSION

 Concomitant use of tamoxifen and potent CYP2D6 inhibiting SSRIs versus other SSRIs was not associated with an increased risk of death.

A systematic review and meta-analysis of prescribing practices of antidepressants in cancer patients

BACKGROUND

Antidepressants are commonly used for the pharmacological treatment of depression. We aimed to summarise the prevalence of antidepressant prescription to cancer patients, and differences by study or patient characteristics.

METHODS

PubMed, Embase, Web of Science, Scopus and psychINFO were searched using keywords 'psychotropic', 'antidepressants', 'prescription' and 'cancer'. Prevalence of antidepressants, type, dose and follow-up of antidepressants and prescriber details were extracted.

RESULTS

Overall, 1537 articles between 1979 and February 2015 were found, 38 met the inclusion criteria and were reviewed according to PRISMA guidelines. The prevalence rate of prescribing antidepressants to cancer patients was 15.6% (95% CI = 13.3-18.3). Prescription was significantly less common in studies from Asia (7.4%; 95% CI = 4.3-12.5), more common in female (22.6%; 95% CI = 16.0-31.0) or breast cancer patients (22.6%; 95% CI = 16.0-30.9). Selective serotonin reuptake inhibitors were the most frequently prescribed antidepressants. General practitioners and psychiatrists, followed by oncologists, were identified as the major providers of antidepressant prescriptions to cancer patients. Few studies reported the exact dose, length of time drugs were prescribed for or follow-up regimens.

CONCLUSIONS

There is considerable variation in the prescribing patterns of antidepressants across the world, with few studies reporting robust data on exact dose or follow-up regimens. Prospective studies that monitor antidepressant prescribing, including details of reasons for prescribing and the healthcare providers involved, dose, change in dose or type of medication and follow-up are needed to ascertain whether patients are being treated optimally and if side effects or drug-drug interactions are identified and managed. Copyright © 2016 John Wiley & Sons, Ltd.

Tamoxifen and Antidepressant Drug Interaction in a Cohort of 16,887 Breast Cancer Survivors

BACKGROUND

Controversy persists about whether certain antidepressants reduce tamoxifen's effectiveness on lowering breast cancer recurrence. We investigated whether taking tamoxifen and antidepressants (in particular, paroxetine) concomitantly is associated with an increased risk of recurrence or contralateral breast cancer.

METHODS

We examined 16 887 breast cancer survivors (TNM stages 0-II) diagnosed between 1996 and 2007 and treated with tamoxifen in two California health plans. Women were followed-up through December 31, 2009, for subsequent breast cancer. The main exposure was the percent of days of overlap when both tamoxifen and an antidepressant (paroxetine, fluoxetine, other selective serotonin reuptake inhibitors, tricyclics, and other classes) were used. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using multivariable Cox regression models with time-varying medication variables.

RESULTS

Of the 16 887 women, half (n = 8099) used antidepressants and 2946 women developed subsequent breast cancer during the 14-year study period. We did not find a statistically significant increased risk of subsequent breast cancer in women who concurrently used paroxetine and tamoxifen. For 25%, 50%, and 75% increases in percent overlap days between paroxetine and tamoxifen, hazard ratios were 1.06 (95% CI = 0.98 to 1.14, P = .09), 1.13 (95% CI = 0.98 to 1.30, P = .09), and 1.20 (95% CI = 0.97 to 1.49, P = .09), respectively, in the first year of tamoxifen treatment but were not statistically significant. Hazard ratios decreased to 0.94 (95% CI = 0.81 to 1.10, P = .46), 0.89 (95% CI = 0.66 to 1.20, P = .46), and 0.85 (95% CI = 0.54 to 1.32, P = .46) by the fifth year (all non-statistically significantly). Absolute subsequent breast cancer rates were similar among women who used paroxetine concomitantly with tamoxifen vs tamoxifen-only users. For the other antidepressants, we again found no such associations.

CONCLUSIONS

Using the comprehensive electronic health records of insured patients, we did not observe an increased risk of subsequent breast cancer in women who concurrently used tamoxifen and antidepressants, including paroxetine.

Early and late long-term effects of adjuvant chemotherapy

Adjuvant chemotherapy continues to play an important role in breast cancer management. Exposure to chemotherapy can lead to a variety of early and late long-term toxicities, including ovarian failure (with resultant infertility and sexual dysfunction), bone loss, weight gain, neurotoxicity, neurocognitive changes, cardiac toxicity and secondary malignancy. Although chemotherapy effects may vary in medical severity, all effects have the potential to lead to a decrease in quality of life and a decrement on overall health status. Improved understanding of the etiology and management of chemotherapy-related toxicity may allow optimization of patient selection for treatment and ameliorate the concerns of patients who are considering embarking on a chemotherapy program. This article presents an overview of relevant early and late long-term toxicities, with a focus on recent advances and clinical management.

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.

How Do Payers Respond to Regulatory Actions? The Case of Bevacizumab

PURPOSE

In February 2008, the US Food and Drug Administration (FDA) granted accelerated approval for bevacizumab for metastatic breast cancer. After public hearings in July 2010, and June 2011, the FDA revoked this approved indication in November 2011, on the basis of additional evidence regarding its risk/benefit profile. The Centers for Medicare and Medicaid Services, local Medicare contractors, and commercial payers varied in their stated intentions to cover bevacizumab after FDA's regulatory actions. We examined payer-specific trends in bevacizumab use after the FDA's regulatory actions.

METHODS

We used outpatient medical claims compiled by IMS Health to evaluate trends in bevacizumab use for breast cancer for Medicare-insured and commercially insured patients (N = 102,906) using segmented regression. Given that Medicare coverage policies may vary across regional contractors, we estimated trends in bevacizumab use across 10 local coverage areas. In a sensitivity analysis, we estimated trends in bevacizumab use for breast cancer compared with trends in use for lung cancer using difference-in-differences models.

RESULTS

Among chemotherapy infusions for breast cancer, bevacizumab use decreased from 31% in July 2010, to 4% in September 2012. Use decreased by 11% among commercially insured and 13% among Medicare-insured patients after July 2010 (interaction P = .68) and continued to decline by 9% per month (interaction P = .61). We observed no contractor-level variation in bevacizumab use among Medicare beneficiaries. During the same period, bevacizumab use for lung cancer was stable.

CONCLUSION

Although insurers varied in public statements regarding coverage intentions, bevacizumab use declined similarly among all payers, suggesting that provider decision making, rather than payer-specific coverage policies, drove reductions.

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.

Control Outcomes and Exposures for Improving Internal Validity of Nonrandomized Studies

OBJECTIVE

Control outcomes and exposures can improve internal validity of nonrandomized studies by assessing residual bias in effect estimates. Control outcomes are those expected to have no treatment effect or the opposite effect of the primary outcome. Control exposures are treatments expected to have no effect on the primary outcome. We review examples of control outcomes and exposures from prior studies and provide recommendations for conducting and reporting these analyses.

DATA SOURCES AND STUDY DESIGN

Review in Google Scholar and Medline of research studies employing control outcomes or exposures. We abstracted publication year, control outcome, control exposure, primary outcome, primary exposure, control outcome/exposure effect, proposed source of bias, and causal criteria.

PRINCIPAL FINDINGS

There is inconsistent terminology for these concepts, making study identification challenging. Six of 11 studies found null associations between treatments and negative control outcomes/exposures, providing greater confidence that the primary study findings were not biased. Five studies found unexpected associations, suggesting bias in the primary association.

CONCLUSIONS

The rigor of nonrandomized studies can be improved with inclusion of control outcomes and exposures for bias detection. Given ongoing concern about clinical and policy inferences from nonrandomized studies, we recommend adoption of these measurement tools.

Racial disparities in initiation of adjuvant endocrine therapy of early breast cancer

Endocrine therapy (ET) is the cornerstone of adjuvant therapy for hormone-receptor positive (HR+) breast cancer. The survival gap between African-American (AA) and white women with breast cancer is most pronounced in HR+ subtypes, and could be related to differences in ET use. The relationship between race and initiation of ET is not well defined. We investigated patterns of ET initiation by race in a diverse cohort of women covered by commercial health insurance. We identified 2,640 women with incident HR+ breast cancer in the North Carolina Central Cancer Registry whose records linked to commercial insurance claims using the Integrated Cancer Information and Surveillance System (ICISS) database. The sample included women age <65 years diagnosed with stage I-III HR+ cancers between 2004 and 2009. We used multivariate Poisson regression to examine the effect of race on likelihood of initiating ET. 14 % of women did not initiate ET within 12 months of diagnosis. AA women were 17 % less likely to initiate ET than whites (aRR 0.83, 95 % CI 0.74-0.93). When analyzed by subset, racial disparities persisted among women who received chemotherapy (aHR 0.67, 95 % CI 0.56-0.80) but not among women who did not receive chemotherapy (aHR 0.96, 95 % CI 0.76-1.21). AA women in our sample were less likely to initiate ET than whites, and this disparity was concentrated among chemotherapy-treated women. ET under-utilization may contribute to the racial survival gap in HR+ breast cancer, and represents an opportunity for intervention to reduce breast cancer disparities.

Psychiatric benefits of integrative therapies in patients with cancer

Integrative oncology uses non-pharmacological adjuncts to mainstream care to manage physical, emotional, and psychological symptoms experienced by cancer survivors. Depression, anxiety, fatigue and pain are among the common, often burdensome symptoms that can occur in clusters, deplete patient morale, interfere with treatment plans, and hamper recovery. Patients already seek various modalities on their own to address a broad range of problems. Legitimate complementary therapies offered at major cancer institutions improve quality of life, speed recovery, and optimize patient support. They also augment the benefits of psychiatric interventions, due to their ability to increase self-awareness and improve physical and psychological conditioning. Further, these integrated therapies provide lifelong tools and develop skills that patients use well after treatment to develop self-care regimens. The active referral of patients to integrative therapies achieves three important objectives: complementary care is received from therapists experienced in working with cancer patients, visits become part of the medical record, allowing treatment teams to guide individuals in maximizing benefit, and patients are diverted from useless or harmful 'alternatives.' We review the reciprocal physical and psychiatric benefits of exercise, mind-body practices, massage, acupuncture, and music therapy for cancer survivors, and suggest how their use can augment mainstream psychiatric interventions.

Efficacy and safety of pharmacotherapy in cancer-related psychiatric disorders across the trajectory of cancer care: a review

At least 25-30% of patients with cancer and an even higher percentage of patients in an advanced phase of illness meet the criteria for a psychiatric diagnosis, including depression, anxiety, stress-related syndromes, adjustment disorders, sleep disorders and delirium. A number of studies have accumulated over the last 35 years on the use of psychotropic drugs as a pillar in the treatment of psychiatric disorders. Major advances in psycho-oncology research have also shown the efficacy of psychotropic drugs as adjuvant treatment of cancer-related symptoms, such as pain, hot flushes, pruritus, nausea and vomiting, fatigue, and cognitive impairment. The knowledge about pharmacokinetics and pharmacodynamics, clinical use, safety, side effects and efficacy of psychotropic drugs in cancer care is essential for an integrated and multidimensional approach to patients treated in different settings, including community-based centres, oncology, and palliative care. A search of the major databases (MEDLINE, Embase, PsycLIT, PsycINFO, the Cochrane Library) was conducted in order to summarize relevant data concerning the efficacy and safety of pharmacotherapy for cancer-related psychiatric disorders in cancer patients across the trajectory of the disease.

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.

Pharmacogenomics of breast cancer therapy: an update

Clinical and histopathologic characteristics of breast cancer have long played an important role in treatment decision-making. Well-recognized prognostic factors include tumor size, node status, presence or absence of metastases, tumor grade, and hormone receptor expression. High tumor grade, presence of hormone receptors, and HER2-positivity are a few predictive markers of response to chemotherapy, endocrine manipulations, and anti-HER2 agents, respectively. However, there is much heterogeneity of outcomes in patients with similar clinical and pathologic features despite equivalent treatment regimens. Some of the differences in response to specific therapies can be attributed to somatic tumor characteristics, such as degree of estrogen receptor expression and HER2 status. In recent years, there has been great interest in evaluating the role that pharmacogenetics/pharmacogenomics, or variations in germline DNA, play in alteration of drug metabolism and activity, thus leading to disparate outcomes among patients with similar tumor characteristics. The utility of these variations in treatment decision-making remains debated. Here we review the data available to date on genomic variants that may influence response to drugs commonly used to treat breast cancer. While none of the variants reported to date have demonstrated clinical utility, ongoing prospective studies and increasing understanding of pharmacogenetics will allow us to better predict risk of toxicity or likelihood of response to specific treatments and to provide a more personalized therapy.