Associations between genetic variants and the effect of letrozole and exemestane on bone mass and bone turnover

Pharmacogenetics of Toxicities Related to Endocrine Treatment in Breast Cancer: A Systematic Review and Meta-analysis

BACKGROUND/AIM

Endocrine therapy is the standard treatment for hormone receptor-positive (HR+) breast cancer (BC). Yet, it is accompanied by treatment-related toxicities, leading to poor treatment adherence, high relapse, and low rates of survival. While pharmacogenomic variants have the potential to guide personalized treatment, their predictive value is inconsistent across published studies.

MATERIALS AND METHODS

To systematically assess the literature's current landscape of pharmacogenomics of endocrine therapy-related adverse drug effects, systematic searches in MEDLINE, Embase, Cochrane CENTRAL, Google Scholar and PharmGKB databases were conducted.

RESULTS

We identified 87 articles. Substantial heterogeneity and variability in pharmacogenomic effects were evident across studies, with many using data from the same cohorts and predominantly focusing on the Caucasian population and postmenopausal women. Meta-analyses revealed Factor V Leiden mutation as a predictor of thromboembolic events in tamoxifen-treated women (p<0.0001). Meta-analyses also found that rs7984870 and rs2234693 were associated with musculoskeletal toxicities in postmenopausal women receiving aromatase inhibitors (p<0.0001 and p<0.0001, respectively).

CONCLUSION

Overall, the current body of evidence regarding the potential role of pharmacogenomics in endocrine therapy-related toxicity in BC remains largely inconclusive. Key concerns include the heterogeneity in toxicity definitions, lack of consideration for genotype-treatment interactions, and the failure to account for multiple testing. The review underscores the necessity for larger and well-designed studies, particularly with the inclusion of premenopausal women and non-Caucasian populations.

SNP of Aromatase Predict Long-term Survival and Aromatase Inhibitor Toxicity in Patients with Early Breast Cancer: A Biomarker Analysis of the GIM4 and GIM5 Trials

PURPOSE

In estrogen receptor-positive (ER+) breast cancer, single-nucleotide polymorphisms (SNP) in the aromatase gene might affect aromatase inhibitors (AI) metabolism and efficacy. Here, we assessed the impact of SNP on prognosis and toxicity of patients receiving adjuvant letrozole.

EXPERIMENTAL DESIGN

We enrolled 886 postmenopausal patients in the study. They were treated with letrozole for 2 to 5 years after taking tamoxifen for 2 to 6 years, continuing until they completed 5 to 10 years of therapy. Germline DNA was genotyped for SNP rs4646, rs10046, rs749292, and rs727479. Log-rank test and Cox model were used for disease-free survival (DFS) and overall survival (OS). Cumulative incidence (CI) of breast cancer metastasis was assessed through competing risk analysis, with contralateral breast cancer, second malignancies and non-breast cancer death as competing events. CI of skeletal and cardiovascular events were assessed using DFS events as competing events. Subdistribution HR (sHR) with 95% confidence intervals were calculated through Fine-Gray method.

RESULTS

No SNP was associated with DFS. Variants rs10046 [sHR 2.03, (1.04-2.94)], rs749292 [sHR 2.11, (1.12-3.94)], and rs727479 [sHR 2.62, (1.17-5.83)] were associated with breast cancer metastasis. Three groups were identified on the basis of the number of these variants (0, 1, >1). Variant-based groups were associated with breast cancer metastasis (10-year CI 2.5%, 7.6%, 10.7%, P = 0.035) and OS (10-year estimates 96.5%, 93.0%, 89.6%, P = 0.030). Co-occurrence of rs10046 and rs749292 was negatively associated with 10-year CI of skeletal events (3.2% vs. 10%, P = 0.033). A similar association emerged between rs727479 and cardiovascular events (0.3% vs. 2.1%, P = 0.026).

CONCLUSIONS

SNP of aromatase gene predict risk of metastasis and AI-related toxicity in ER+ early breast cancer, opening an opportunity for better treatment individualization.

Genetic overlap for ten cardiovascular diseases: A comprehensive gene-centric pleiotropic association analysis and Mendelian randomization study

Recent studies suggest that pleiotropic effects may explain the genetic architecture of cardiovascular diseases (CVDs). We conducted a comprehensive gene-centric pleiotropic association analysis for ten CVDs using genome-wide association study (GWAS) summary statistics to identify pleiotropic genes and pathways that may underlie multiple CVDs. We found shared genetic mechanisms underlying the pathophysiology of CVDs, with over two-thirds of the diseases exhibiting common genes and single-nucleotide polymorphisms (SNPs). Significant positive genetic correlations were observed in more than half of paired CVDs. Additionally, we investigated the pleiotropic genes shared between different CVDs, as well as their functional pathways and distribution in different tissues. Moreover, six hub genes, including ALDH2, XPO1, HSPA1L, ESR2, WDR12, and RAB1A, as well as 26 targeted potential drugs, were identified. Our study provides further evidence for the pleiotropic effects of genetic variants on CVDs and highlights the importance of considering pleiotropy in genetic association studies.

Breast cancer pharmacogenetics: a systematic review

Breast cancer was declared the most prevalent type of cancer in 2020. Among other factors, treatment response can be affected by genetic polymorphisms - which is the focus of pharmacogenetics - and ethnicity is also a contributing factor in this context. Relevant genes in disease treatment pathways were selected to evaluate treatment response from the pharmacogenetic perspective; polymorphism frequencies and ethnic and continental representation across the available literature were also assessed through a systematic review. The identified associations and gaps have been described in this study with the purpose that, in the future, treatments can be personalized and thus be more effective, safer, and accessible to all.

Aromatase and CDK4/6 Inhibitor-Induced Musculoskeletal Symptoms: A Systematic Review

BACKGROUND

Treatment with aromatase inhibitors (AIs) is fundamental in women with hormone receptor-positive breast cancer in the adjuvant as well as the metastatic setting. Even though it is considered to be a well-tolerated therapy, aromatase inhibitor-associated musculoskeletal syndrome (AIMSS) is the most common adverse event encountered by breast cancer patients. CDK4/6 inhibitors have emerged as a new treatment strategy in metastatic hormone receptor-positive breast cancer. However, the impact of CDK4/6 inhibitors on musculoskeletal symptoms caused by AIs is not well-defined.

OBJECTIVES

This systematic review aims to identify the frequency of joint symptoms induced by treatment with AIs and CDK4/6 inhibitors in the metastatic setting.

SEARCH STRATEGY

Eligible articles were identified by a search of existing literature for the period 2005/01/01-2021/01/01; The algorithm consisted of a predefined combination of the following keywords "breast", "cancer", "aromatase inhibitors", "CDK4/6", "phase III".

SELECTION CRITERIA

This study was performed in accordance with PRISMA guidelines. All randomized controlled Phase III trials (RCTs) evaluating the administration of third-generation aromatase inhibitors (AIs) and CDK4/6 inhibitors in postmenopausal women in the metastatic setting were considered eligible for this review.

DATA COLLECTION

Overall, 16 randomized control trials (RCTs) were retrieved, of which nine studies explored the administration of AIs in the metastatic setting and seven studies investigated the combination of CDK4/6 inhibitors and AIs. Arthralgia was reported in 1-47% of patients treated with AIs and 5.8-33.3% of patients treated with CDK4/6 inhibitors. Myalgias occurred in 2-23.7% of patients receiving AIs compared with 4.8-11.9% of patients treated with CDK4/6 inhibitors. The incidence of back pain was 7-32.9% vs. 2.9-8.5% in postmenopausal women with metastatic disease treated with AIs and CDK4/6 inhibitors, respectively. Bone pain was reported in 7-32.9% of postmenopausal women treated with AIs and 2.9-8.5% of women treated with CDK4/6 inhibitors.

CONCLUSIONS

AI treatment-induced musculoskeletal syndrome is an adverse event affecting over one-third (20-47%) of postmenopausal patients treated with AIs that often leads to treatment discontinuation. Data from RCTs provide evidence that the incidence of musculoskeletal symptoms is relatively decreased upon CDK4/6 inhibitor administration. CDK4/6 inhibitors may provide a protective role against AIMSS development.

Aromatase Inhibitor-Associated Musculoskeletal Syndrome: Understanding Mechanisms and Management

Aromatase inhibitors (AIs) are a key component in the chemoprevention and treatment of hormone receptor-positive (HR+) breast cancer. While the addition of AI therapy has improved cancer-related outcomes in the management of HR+ breast cancer, AIs are associated with musculoskeletal adverse effects known as the aromatase inhibitor-associated musculoskeletal syndrome (AIMSS) that limit its tolerability and use. AIMSS is mainly comprised of AI-associated bone loss and arthralgias that affect up to half of women on AI therapy and detrimentally impact patient quality of life and treatment adherence. The pathophysiology of AIMSS is not fully understood though has been proposed to be related to estrogen deprivation within the musculoskeletal and nervous systems. This review aims to characterize the prevalence, risk factors, and clinical features of AIMSS, and explore the syndrome's underlying mechanisms and management strategies.

Aromatase Inhibitors-Induced Musculoskeletal Disorders: Current Knowledge on Clinical and Molecular Aspects

Aromatase inhibitors (AIs) have radically changed the prognosis of hormone receptor positive breast cancer (BC) in post-menopausal women, and are a mainstay of the adjuvant therapy for BC after surgery in place of, or following, Tamoxifen. However, AIs aren't side effect-free; frequent adverse events involve the musculoskeletal system, in the form of bone loss, AI-associated arthralgia (AIA) syndrome and autoimmune rheumatic diseases. In this narrative review, we reported the main clinical features of these three detrimental conditions, their influence on therapy adherence, the possible underlying molecular mechanisms and the available pharmacological and non-pharmacological treatments. The best-known form is the AIs-induced osteoporosis, whose molecular pathway and therapeutic possibilities were extensively investigated in the last decade. AIA syndrome is a high prevalent joint pain disorder which often determines a premature discontinuation of the therapy. Several points still need to be clarified, as a universally accepted diagnostic definition, the pathogenetic mechanisms and satisfactory management strategies. The association of AIs therapy with autoimmune diseases is of the utmost interest. The related literature has been recently expanded, but many issues remain to be explored, the first being the molecular mechanisms.

Management of osteoporosis in women with breast cancer

The screening, prevention and treatment of osteoporosis are similar in women with or without breast cancer. Breast cancer treatments, such as aromatase inhibitors, chemotherapy-induced ovarian failure and gonadotropin-releasing hormone antagonists all decrease estrogen levels, which in turn causes net bone resorption and bone loss. Bone loss over time will be of sufficient magnitude to cause some women to experience fractures. Thus, osteoporosis is an equation; the peak bone mass achieved by age 30 years minus the age-related and menopausal bone loss. Women should have their bone density measured by dual x-ray absorptiometry scans every 2 years. As clinically indicated, women should receive anti-osteoporosis drugs such as zoledronic acid, denosumab or oral bisphosphonates.

Association of CYP19A1 gene variations with adjuvant letrozole-induced adverse events in South Indian postmenopausal breast cancer cohort expressing hormone-receptor positivity

PURPOSE

Musculoskeletal adverse events (MS-AEs) and vasomotor symptoms (VMSs) are the major side-effects of newer generation non-steroidal aromatase inhibitor (AI), letrozole. Single-nucleotide polymorphisms (SNPs) in CYP19A1 gene coding for the enzyme aromatase are related to AI treatment-associated adverse drug reactions. Therefore, we aimed to determine whether SNPs in the CYP19A1 gene are associated with adjuvant letrozole-induced 'specific' AEs in postmenopausal hormone receptor-positive (HR+) breast cancer patients.

METHODS

Genomic DNA was isolated from 198 HR+ breast cancer patients by the phenol-chloroform method, and eleven SNPs in the CYP19A1 gene were genotyped by TaqMan genotyping assays on the qRT-PCR system. Toxicity was assessed according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 3.0, and the data were analyzed using SPSS v19.0 and Haploview v4.2 statistical software.

RESULTS

Subjects carrying the genetic variants of CYP19A1 gene SNP rs700519 had significantly higher odds (OR 2.33; 95% CI [1.29-4.20], P = 0.0057) of MS-AEs under dominant statistical effect. The frequency of the two distinct haplotypes that include the variant allele 'T' at rs700519 locus, H5-GCTATCTGGCG (P = 0.042) and H11-GCTATTGCACG (P = 0.013) were significantly higher in patients with musculoskeletal toxicity than in those without MS-AEs and thus predisposing to MS-AEs. Similarly, H6-GCCAGCTGGCG (P = 0.037) haplotype exhibited higher frequencies in patients presented with VMSs. However, no such association was observed between CYP19A1 genotypes and VMSs.

CONCLUSIONS

To the best of our knowledge, this is the first study assessing the impact of CYP19A1 genetic variations with adjuvant letrozole treatment-associated AEs in Indian women. Genetic variations in the CYP19A1 gene is associated with letrozole-induced AEs and warrants further investigation in larger cohorts to validate this finding.

A New Genetic Risk Score to Predict the Outcome of Locally Advanced or Metastatic Breast Cancer Patients Treated With First-Line Exemestane: Results From a Prospective Study

INTRODUCTION

Approximately 50% of locally advanced or metastatic breast cancer (MBC) patients treated with first-line exemestane do not show objective response and currently there are no reliable biomarkers to predict the outcome of patients using this therapy. The constitutive genetic background might be responsible for differences in the outcome of exemestane-treated patients. We designed a prospective study to investigate the role of germ line polymorphisms as biomarkers of survival.

PATIENTS AND METHODS

Three hundred two locally advanced or MBC patients treated with first-line exemestane were genotyped for 74 germ line polymorphisms in 39 candidate genes involved in drug activity, hormone balance, DNA replication and repair, and cell signaling pathways. Associations with progression-free survival (PFS) and overall survival (OS) were tested with multivariate Cox regression. Bootstrap resampling was used as an internal assessment of results reproducibility.

RESULTS

Cytochrome P450 19A1-rs10046TC/CC, solute carrier organic anion transporter 1B1-rs4149056TT, adenosine triphosphate binding cassette subfamily G member 2-rs2046134GG, fibroblast growth factor receptor-4-rs351855TT, and X-ray repair cross complementing 3-rs861539TT were significantly associated with PFS and then combined into a risk score (0-1, 2, 3, or 4-6 risk points). Patients with the highest risk score (4-6 risk points) compared with ones with the lowest score (0-1 risk points) had a median PFS of 10 months versus 26.3 months (adjusted hazard ratio [AdjHR], 3.12 [95% confidence interval (CI), 2.18-4.48]; P < .001) and a median OS of 38.9 months versus 63.0 months (AdjHR, 2.41 [95% CI, 1.22-4.79], P = .012), respectively.

CONCLUSION

In this study we defined a score including 5 polymorphisms to stratify patients for PFS and OS. This score, if validated, might be translated to personalize locally advanced or MBC patient treatment and management.

Exemestane may be less detrimental than letrozole to bone health in women homozygous for the UGT2B17*2 gene deletion

PURPOSE

UGT2B17 gene deletion (UGT2B17*2) has been reported to affect bone health as well as the pharmacokinetics of aromatase inhibitor (AI) drugs such as exemestane. The goal of this study was to assess associations between UGT2B17 gene deletion and bone health prior to and after 24 months of AI treatment in postmenopausal women with hormone receptor positive (HR+) breast cancer.

METHODS

Bone health in women with HR+ breast cancer enrolled on the prospective randomized Exemestane and Letrozole Pharmacogenetics (ELPh) trial was determined by measuring bone turnover markers (BTM) and bone mineral density (BMD) pre-treatment and after 3 BTM and 24 BMD months of treatment with either the steroidal AI exemestane or the nonsteroidal AI letrozole. DNA samples were genotyped for UGT2B17*2.

RESULTS

Of the 455 subjects included in the analyses, 244 (53.6%) carried at least one copy of UGT2B17*2. UGT2B17*2 was associated with lower pre-treatment BMD at the hip (P = 0.01) and spine (P = 0.0076). Letrozole treatment was associated with a greater decrease in BMD of the hip (P = 0.03) and spine (P = 0.03) than exemestane. UGT2B17 genotype was not associated with changes in BMD from 24 months of AI treatment, though in UGT2B17*2 homozygous patients, there was a trend toward greater decreases in BMD of the spine from treatment with letrozole compared with exemestane (P = 0.05).

CONCLUSION

UGT2B17*2 may be associated with lower baseline BMD in women with HR+ breast cancer. Exemestane is less detrimental to bone health than letrozole in postmenopausal women treated with AI, and this effect may be confined to patients carrying UGT2B17*2, though this finding requires independent validation.

The Roles of Common Variation and Somatic Mutation in Cancer Pharmacogenomics

Cancer pharmacogenomics is the science concerned with understanding genetic alterations and its effects on the pharmacokinetics and pharmacodynamics of anti-cancer drugs, with the aim to provide cancer patients with the precise medication that will achieve a good response and cause low/no incidence of adverse events. Advances in biotechnology and bioinformatics have enabled genomic research to evolve from the evaluation of alterations at the single-gene level to studies on the whole-genome scale using large-scale genotyping and next generation sequencing techniques. International collaborative efforts have resulted in the construction of databases to curate the identified genetic alterations that are clinically significant, and these are currently utilized in clinical sequencing and liquid biopsy screening/monitoring. Furthermore, countless clinical studies have accumulated sufficient evidence to match cancer patients to therapies by utilizing the information of clinical-relevant alterations. In this review we summarize the importance of germline alterations that act as predictive biomarkers for drug-induced toxicity and drug response as well as somatic mutations in cancer cells that function as drug targets. The integration of genomics into the medical field has transformed the era of cancer therapy from one-size-fits-all to cancer precision medicine.

Osteoporosis and musculoskeletal complications related to therapy of breast cancer

Aromatase inhibitors (AIs) are the treatment of choice for the majority of postmenopausal women with estrogen receptor (ER) positive breast cancers in early and advanced stage settings. One of most frequent side effects of AIs is bone loss that is of sufficient magnitude to increase risk of osteoporotic fractures. Osteoporosis is primarily a complex genetic disease with few modifiable risk factors. As the lifespan increases, and breast mortality decreases, more women with breast cancer will be at risk of osteoporotic fractures, or falls that result in fractures. The screening, prevention, and treatment of osteoporosis do not differ in women with or without breast cancer. Rather, breast cancer treatments, including AIs, chemotherapy-induced ovarian failure, and gonadotropin-releasing hormone (GnRH) agonists, all decrease estrogen, which causes net bone resorption, leading some women to experience fracture. Occurring in about fifty-percent of women, AI-induced arthralgia is one of the most common side effects, and causes of nonadherence and discontinuation. Registry studies show that nonadherence and discontinuation may contribute to higher breast cancer mortality. Thus, understanding the mechanisms, risk factors, and interventions to mitigate symptoms of AI-induced arthralgia is a high priority.

Personalizing aromatase inhibitor therapy in patients with breast cancer

BACKGROUND

Aromatase inhibitors are the mainstay of therapy for patients with hormone receptor-positive breast cancer in both adjuvant and metastatic settings. Their use in clinical practice has been challenged by significant inter-individual variability in response and tolerability. Hence, the purpose of this paper is to provide a succinct review of the literature on the genetic factors contributing to this variability.

DESIGN

A systematic search in PUBMED was conducted to identify studies that investigated the association between germline polymorphisms and disposition, clinical response and toxicities of aromatase inhibitors, as well as those evaluating the implications of mutations in ESR1 on clinical response.

RESULTS

Polymorphisms in genes coding for phase I and phase II enzymes (pharmacokinetic genes) significantly modulated exposure to aromatase inhibitors; however, there is a paucity of data linking interindividual variability in drug exposure to clinical response. Furthermore, pharmacogenetic studies interrogating relationship between polymorphisms in CYP19A1 (the target site of aromatase inhibitors, i.e. a pharmacodynamic gene) and response yielded conflicting results. Acquired mutations in ESR1 receptors have been identified as the underlying mechanism of resistance to aromatase inhibitors, and likely predict drug response. Although some pharmacogenetic studies have implicated polymorphisms in CYP19A1 and ESR1 with drug-related side effects, the putative role of these genes in predicting toxicity warrants further validation.

CONCLUSION

Genetic polymorphisms in pharmacokinetic and pharmacodynamic genes appear to influence aromatase inhibitor disposition, response and/or toxicity; however, prospective interventional studies are needed to understand the application of genomics to personalize aromatase inhibitor therapy in breast cancer patients.

Long-term effect of exemestane therapy on bone mineral density supported by bisphosphonates: Results of 5-year adjuvant treatment in postmenopausal women with early-stage breast cancer

PURPOSE

Unlike anastrozole, the effect of long-term exemestane (EXE) therapy on bone mineral density (BMD) is still unknown. We assessed changes in BMD from baseline to 5 years of EXE treatment.

METHODS

Postmenopausal women with endocrine-responsive breast cancer receiving EXE as adjuvant therapy were enrolled in this study. EXE was administered for 5 years. The BMD of the lumbar spine (LS) and femoral neck (FN) was assessed by dual-energy X-ray absorptiometry at baseline and after 6 months and 1, 2, 3, 4, 5 and 6 years. Oral bisphosphonate (Bis) treatment was initiated when patients were diagnosed with osteoporosis with a T-score of -2.5 or lower.

RESULTS

Eighty-one patients were enrolled in the study between 2005 and 2010. The median follow-up period was 54.9 months. Forty-two patients were administered Bis. Overall, the BMD of the LS increased by 7.3% from baseline and that of the FN increased by 3.4% with 5 years of EXE treatment. At the sixth year (i.e. 1 year after the treatment), BMD of the LS increased by 7.2% and that of the FN increased by 5.7%. Furthermore, the BMD of the FN increased by 12.0% in patients treated upfront with Bis and by 1.2% in those not treated with Bis (P = 0.0262). Fractures developed in nine patients (11.1%) and seven (8.6%) had fragility fractures.

CONCLUSION

Oral Bis improves BMD of the FN in patients with osteoporosis. Five-year EXE treatment with proper addition of Bis helps maintain the BMD of the LS and FN at the sixth year.

Variable aromatase inhibitor plasma concentrations do not correlate with circulating estrogen concentrations in post-menopausal breast cancer patients

PURPOSE

The aromatase inhibitors (AI) exemestane (EXE), letrozole (LET), and anastrozole suppress estrogen biosynthesis, and are effective treatments for estrogen receptor (ER)-positive breast cancer. Prior work suggests that anastrozole blood concentrations are associated with the magnitude of estrogen suppression. The objective of this study was to determine whether the magnitude of estrogen suppression, as determined by plasma estradiol (E2) concentrations, in EXE or LET treated patients is associated with plasma AI concentrations.

METHODS

Five hundred post-menopausal women with ER-positive breast cancer were enrolled in the prospective Exemestane and Letrozole Pharmacogenetic (ELPh) Study conducted by the COnsortium on BReast cancer phArmacogomics (COBRA) and randomly assigned to either drug. Estrogen concentrations were measured at baseline and after 3 months of AI treatment and drug concentrations were measured after 1 or 3 months. EXE or LET concentrations were compared with 3-month E2 concentration or the change from baseline to 3 months using several complementary statistical procedures.

RESULTS

Four-hundred patients with on-treatment E2 and AI concentrations were evaluable (EXE n = 200, LET n = 200). Thirty (7.6%) patients (EXE n = 13, LET n = 17) had 3-month E2 concentrations above the lower limit of quantification (LLOQ) (median: 4.75; range: 1.42-63.8 pg/mL). EXE and LET concentrations were not associated with on-treatment E2 concentrations or changes in E2 concentrations from baseline (all p > 0.05).

CONCLUSIONS

Steady-state plasma AI concentrations do not explain variability in E2 suppression in post-menopausal women receiving EXE or LET therapy, in contrast with prior evidence in anastrozole treated patients.

Estrogen receptors in breast and bone: from virtue of remodeling to vileness of metastasis

Bone metastasis is a prominent cause of morbidity and mortality in cancer. High rates of bone colonization in breast cancer, especially in the subtype expressing estrogen receptors (ERs), suggest tissue-specific proclivities for metastatic tumor formation. The mechanisms behind this subtype-specific organ-tropism remains largely elusive. Interestingly, as the major driver of ER+ breast cancer, ERs also have important roles in bone development and homeostasis. Thus, any agents targeting ER will also inevitably affect the microenvironment, which involves the osteoblasts and osteoclasts. Yet, how such microenvironmental effects are integrated with direct therapeutic responses of cancer cells remain poorly understood. Recent findings on ER mutations, especially their enrichment in bone metastasis, raised even more provocative questions on the role of ER in cancer-bone interaction. In this review, we evaluate the importance of ERs in bone metastasis and discuss new avenues of investigation for bone metastasis treatment based on current knowledge.

Institutional profile of pharmacogenetics within University of Michigan College of Pharmacy

The University of Michigan College of Pharmacy has made substantial investment in the area of pharmacogenomics to further bolster its activity in pharmacogenomics research, implementation and education. Four tenure-track faculty members have active research programs that focus primarily on the discovery of functional polymorphisms (HJ Zhu), and genetic associations with treatment outcomes in patients with cancer (DL Hertz), cardiovascular disease (JA Luzum) and psychiatric conditions (VL Ellingrod). Recent investments from the University and the College have accelerated the implementation of pharmacogenetics broadly across the institution and in targeted therapeutic areas. Students within the PharmD and other health science professions receive substantial instruction in pharmacogenomics, in preparation for careers in biomedical health in which they can contribute to the generation, dissemination and utilization of pharmacogenomics knowledge to improve patient care.

Pharmacogenetics and aromatase inhibitor induced side effects in breast cancer patients

This paper reviews genetic variations mainly related to the onset of adverse events during aromatase inhibitors in early breast cancer. Genetic variability could occur at different steps. The analysis included studies that involved breast cancer patients, treated with an aromatase inhibitor, genotyped for CYP19A1 and/or CYP17A1 and/or CYP27B1 and/or TCLA1, and/or RANK/RANKL/OPG and/or ESR1/ESR2, and assessed for toxicity profile. Twenty-two articles were included for the analysis. Three studies evaluated outcomes and adverse events; 19 studies assessed only side effects. Functional variations may be useful in predicting the onset of toxicities. The identification of polymorphisms at increased risk of toxicity may enable patient management. However, more data are needed to be applied in the individualization of treatment in daily practice.

Germline genetic predictors of aromatase inhibitor concentrations, estrogen suppression and drug efficacy and toxicity in breast cancer patients

The third-generation aromatase inhibitors (AIs), anastrozole, letrozole and exemestane, are highly effective for the treatment of estrogen receptor-positive breast cancer in postmenopausal women. AIs inhibit the aromatase (CYP19A1)-mediated production of estrogens. Most patients taking AIs achieve undetectable blood estrogen concentrations resulting in drug efficacy with tolerable side effects. However, some patients have suboptimal outcomes, which may be due, in part, to inherited germline genetic variants. This review summarizes published germline genetic associations with AI treatment outcomes including systemic AI concentrations, estrogenic response to AIs, AI treatment efficacy and AI treatment toxicities. Significant associations are highlighted with commentary about prioritization for future validation to identify pharmacogenetic predictors of AI treatment outcomes that can be used to inform personalized treatment decisions in patients with estrogen receptor-positive breast cancer.

ESR1 and PGR polymorphisms are associated with estrogen and progesterone receptor expression in breast tumors

Hormone receptor-positive (HR+) breast cancers express the estrogen (ERα) and/or progesterone (PgR) receptors. Inherited single nucleotide polymorphisms (SNPs) in ESR1, the gene encoding ERα, have been reported to predict tamoxifen effectiveness. We hypothesized that these associations could be attributed to altered tumor gene/protein expression of ESR1/ERα and that SNPs in the PGR gene predict tumor PGR/PgR expression. Formalin-fixed paraffin-embedded breast cancer tumor specimens were analyzed for ESR1 and PGR gene transcript expression by the reverse transcription polymerase chain reaction based Oncotype DX assay and for ERα and PgR protein expression by immunohistochemistry (IHC) and an automated quantitative immunofluorescence assay (AQUA). Germline genotypes for SNPs in ESR1 (n = 41) and PGR (n = 8) were determined by allele-specific TaqMan assays. One SNP in ESR1 (rs9322336) was significantly associated with ESR1 gene transcript expression (P = 0.006) but not ERα protein expression (P > 0.05). A PGR SNP (rs518162) was associated with decreased PGR gene transcript expression (P = 0.003) and PgR protein expression measured by IHC (P = 0.016), but not AQUA (P = 0.054). There were modest, but statistically significant correlations between gene and protein expression for ESR1/ERα and PGR/PgR and for protein expression measured by IHC and AQUA (Pearson correlation = 0.32-0.64, all P < 0.001). Inherited ESR1 and PGR genotypes may affect tumor ESR1/ERα and PGR/PgR expression, respectively, which are moderately correlated. This work supports further research into germline predictors of tumor characteristics and treatment effectiveness, which may someday inform selection of hormonal treatments for patients with HR+ breast cancer.

The implications of genetic variation for the pharmacokinetics and pharmacodynamics of aromatase inhibitors

INTRODUCTION

Breast cancer is the most common female cancer and remains a serious public health concern worldwide. Third-generation aromatase inhibitors (AIs) are widely used in postmenopausal women with estrogen receptor positive breast cancer. However, there is marked interindividual variability in terms of the efficacy and incidence of adverse events following treatment with AIs. Pharmacogenetics has the potential to predict clinical outcomes based on patients' genetic information, paving the way towards personalized treatment.

AREAS COVERED

This article reviews pharmacogenetic studies of AIs, including pharmacokinetic and pharmacodynamic aspects, highlighting those studies where the efficacy and adverse events of AIs have been examined using both candidate gene and genome-wide approaches.

EXPERT OPINION

Pharmacogenetics is a promising approach to develop personalized medicine with AIs. However, the application of pharmacogenetics to predict therapeutic efficacy and adverse events in breast cancer patients is still far from implementation in routine clinical practice. Large, comprehensive, multicenter studies that simultaneously evaluate multiple genes and pathways, including rare variants, are warranted in order to produce reliable and informative results. The ultimate aim is to develop clinically-relevant guidelines for breast cancer therapy.