Estrogen receptor genotypes, menopausal status, and the lipid effects of tamoxifen

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.

Serum Cholesterol Level Changes during Gonadotropin-Releasing Hormone-Agonist Therapy in Premenopausal Female Patients with Breast Cancer

OBJECTIVES

To investigate the changes in cholesterol levels during medical ovarian suppression.

METHODS

We reviewed the medical records and blood test results of 187 female patients with breast cancer who underwent gonadotropin-releasing hormone (GnRH)-agonist therapy for > 24 weeks at our hospital between 1 January 2018 and 31 December 2020. The study excluded patients in this cohort who had previously been diagnosed with dyslipidemia, diabetes, or had recently received lipid-lowering agents, resulting in a final sample size of 152 participants. The age at diagnosis and preoperative body mass index (BMI) were included as baseline demographics. A generalized additive mixed model was applied to analyze the relationship between the duration of GnRH-agonist treatment and changes in cholesterol levels.

RESULTS

The study participants had a mean age of 42.5 ± 5.2 years and a mean preoperative BMI of 23.0 ± 3.6 kg/m²; the mean GnRH-agonist therapy duration was 19.3 months (range: 5.6-37.7 months); and the total cholesterol level before GnRH-agonist treatment was 171 mg/dL that was significantly higher at 181 mg/dL (P = 0.03) during the most recent measurement. The total cholesterol level was unaffected by the GnRH-agonist therapy until 19.3 months after which it significantly increased by 1.28 mg/dL per month (P = 0.011). There was no significant effect of age, preoperative BMI, or the glomerular filtration rate on the total cholesterol levels.

CONCLUSIONS

Long-term GnRH agonist therapy for > 19 months can cause a significant increase in the serum cholesterol levels. To prevent complications, patients receiving the treatment should be informed and monitored for the possible progression of dyslipidemia.

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.

Comparison of changes in lipid profiles of premenopausal women with early-stage breast cancer treated with different endocrine therapies

Adjuvant endocrine therapy improves the prognosis of early breast cancer with hormone receptor positivity. However, there is no systematic report on the effect of endocrine therapy (particularly ovarian function suppression, OFS) on serum lipids in premenopausal women. This retrospective cohort study aimed to determine whether various endocrine treatments had different effects on blood lipids. This study enrolled 160 premenopausal patients with stage I-III breast cancer in eastern China. The initial diagnostic information was retrieved from patient's medical records, including age at the time of diagnosis, tumor characteristics, anticancer treatment and past medical history. The changes in blood lipids in patients receiving different types of endocrine therapy were compared at the 3rd, 6th, 12th, and 24th months after initiating endocrine therapy. Generalized linear mixed model was used in our analyses. Our data revealed that low-density lipoprotein cholesterol (LDL-C) levels in patients with tamoxifen (TAM) were significantly lower in the 6th, 12th, and 24th months than that in the 3rd month, while high-density lipoprotein cholesterol (HDL-C) levels in the 6th, 12th, and 24th months were significantly higher than that in the 3rd month, indicating that blood lipid levels generally improved with time. While in TAM plus OFS group, HDL-C levels were significantly higher in the 24th month than in the 3rd month, total cholesterol (TC) levels were significantly higher in the 24th month than in the 6th month. The lipid profiles of OFS plus aromatase inhibitor (AI) group did not show significant differences at any time point but were significantly higher than those of the other two groups especially in LDL and TC. TAM group tended to have lower serum lipid levels. With longer follow-up, no statistically significant difference in values was observed between TAM and TAM plus OFS groups at various time points. Compared with the other two groups, OFS plus AI group presented an increasing trend toward LDL-C and TC. The risk of dyslipidemia requires further investigation using a large sample size.

Is the beta estradiol receptor receiving enough attention for its metabolic importance in postmenopause?

The relationship between menopause and the development of metabolic diseases is well established. In postmenopause women, there is an expansion of visceral white adipose tissue (WATv), which highly contributes to the rise of circulating lipids. Meanwhile, muscle glucose uptake decreases and hepatic glucose production increases. Consequently, in the pancreas, lipotoxicity and glycotoxicity lead to deficient insulin production. These factors initiate an energy imbalance and enhance the probability of developing cardiovascular and metabolic diseases. Although the activation of estradiol receptors (ER) has been shown to be beneficial for the WAT stock pattern, leading to the insulin-sensitive phenotype, authors have described the risk of these receptors' activation, contributing to neoplasia development. The selective activation of beta-type ER (ERβ) seems to be a promising strategy in the treatment of energy imbalance, acting on several tissues of metabolic importance and allowing an intervention with less risk for the development of estrogen-dependent neoplasia. However, the literature on the risks and benefits of selective ERβ activation still needs to increase. In this review, several aspects related to ERβ were considered, such as its physiological role in tissues of energy importance, beneficial effects, and risks of its stimulation during menopause. PubMed, SciELO, Cochrane, and Medline/Bireme databases were used in this study.

An exploratory analysis on the influence of genetic variants on weight gain among etonogestrel contraceptive implant users

OBJECTIVE

To identify genetic variants associated with weight gain related to etonogestrel contraceptive implant use.

STUDY DESIGN

We conducted a retrospective analysis from a parent pharmacogenomic study of healthy, reproductive-aged women using etonogestrel implants. We reviewed medical records to calculate objective weight changes from implant insertion to study enrollment and asked participants about subjective weight gain (yes/no) during contraceptive implant use. We used genotyping data (99 genetic variants) from the parent study to conduct backward-stepwise generalized linear modeling to identify genetic variants associated with objective weight changes.

RESULTS

Among 276 ethnically diverse participants, median body-mass index (BMI) was 25.8 kg/m² (range 18.5-48.1). We found a median weight change of +3.2 kg (range -27.6 to +26.5) from implant insertion to study enrollment. Report of subjective weight gain had minimal agreement with measured weight gain during implant use (Cohen's kappa = 0.21). Our final generalized linear model contained two variables associated with objective weight change that met conservative statistical significance (p < 5.0 × 10^-4). Participants with two copies (homozygous) of the ESR1 rs9340799 variant on average gained 14.1 kg more than all other participants (p = 1.4 × 10^-4). Higher enrollment BMI was also associated with objective weight gain (β = 0.54, p = 9.4 × 10^-12).

CONCLUSION

Genetic variants in the estrogen receptor 1 (ESR1) do not have known associations with obesity or metabolic syndrome, but there is physiologic plausibility for a progestin-mediated genetic association between ESR1 and weight gain. Additional genetic research is needed to substantiate our findings and elucidate further advances in individualized counseling on the risk of weight gain with exogenous steroid hormones.

IMPLICATIONS

Genetic variation in the estrogen receptor 1 gene may account for variability in weight gain among etonogestrel contraceptive implant users. If these findings can be replicated with other progestin-containing medications, we may be able to better individualize contraceptive counseling.

ESR1 and ESR2 polymorphisms in the BIG 1-98 trial comparing adjuvant letrozole versus tamoxifen or their sequence for early breast cancer

Estrogen receptor 1 (ESR1) and ESR2 gene polymorphisms have been associated with endocrine-mediated physiological mechanisms, and inconsistently with breast cancer risk and outcomes, bone mineral density changes, and hot flushes/night sweats. DNA was isolated and genotyped for six ESR1 and two ESR2 single-nucleotide polymorphisms (SNPs) from tumor specimens from 3691 postmenopausal women with hormone receptor-positive breast cancer enrolled in the BIG 1-98 trial to receive tamoxifen and/or letrozole for 5 years. Associations with recurrence and adverse events (AEs) were assessed using Cox proportional hazards models. 3401 samples were successfully genotyped for five SNPs. ESR1 rs9340799(XbaI) (T>C) variants CC or TC were associated with reduced breast cancer risk (HR = 0.82,95% CI = 0.67-1.0), and ESR1 rs2077647 (T>C) variants CC or TC was associated with reduced distant recurrence risk (HR = 0.69, 95% CI = 0.53-0.90), both regardless of the treatments. No differential treatment effects (letrozole vs. tamoxifen) were observed for the association of outcome with any of the SNPs. Letrozole-treated patients with rs2077647 (T>C) variants CC and TC had a reduced risk of bone AE (HR = 0.75, 95% CI = 0.58-0.98, P interaction = 0.08), whereas patients with rs4986938 (G>A) genotype variants AA and AG had an increased risk of bone AE (HR = 1.37, 95% CI = 1.01-1.84, P interaction = 0.07). We observed that (1) rare ESR1 homozygous polymorphisms were associated with lower recurrence, and (2) ESR1 and ESR2 SNPs were associated with bone AEs in letrozole-treated patients. Genes that are involved in estrogen signaling and synthesis have the potential to affect both breast cancer recurrence and side effects, suggesting that individual treatment strategies can incorporate not only oncogenic drivers but also SNPs related to estrogen activity.

Evaluation of endometrial thickness and bone mineral density based on CYP2D6 polymorphisms in Turkish breast cancer patients receiving tamoxifen treatment

BACKGROUND

Several previous studies have examined the effect of CYP2D6 gene polymorphism on the efficacy and metabolism of tamoxifen (Tamoxifen Teva, Nolvadex) in the treatment of breast cancer. In the present study, the metabolic profiles associated with various CYP2D6 genotypes were evaluated.

METHOD

In the present study 92 Turkish breast cancer patients with early-stage hormone receptor-positive tumors treated with adjuvant tamoxifen (20 mg) were evaluated for CYP2D6 genotype and metabolic profiles. Known side effects of tamoxifen treatment, including endometrial thickening, changes in serum lipid levels and bone density, and hepatosteatosis, were evaluated according to the CYP2D6 polymorphism.

RESULT

The distribution of metabolic characteristics in the Turkish population was as follows: 77.1% normal metabolism, 11.5% intermediate metabolism, 5.2% ultrarapid metabolism, and 2.1% poor metabolism. The CYP2D6 genotypes associated with rapid metabolism were CYP2D6 3X*1/*1 duplication (DUP) and CYP2D6 2X*1/*2, while poor metabolism was associated with the genotypes CYP2D6 *3/*4 and CYP2D6 *6/*6. There was no statistically significant relationship between metabolic characteristics and bone density or hepatosteatosis. A statistically significant difference in total cholesterol and triglycerides was detected in lipid profile analysis (p = 0.003, p = 0.02). Assessment of endometrial thickness revealed a significant association of hyperplasia and poor metabolism, and an association between atrophy and ultrarapid metabolism (p = 0.01).

CONCLUSION

Significant development of endometrial hyperplasia was identified among individuals with poor tamoxifen metabolism. As a result, tamoxifen may be a significant predictor of endometrial thickening among individuals with poor metabolic characteristics.

A review on the role of L-carnitine in the management of tamoxifen side effects in treated women with breast cancer

L-carnitine is an antioxidant and is found to be a protective agent against many diseases including cancer. This review illustrates the possible role of L-carnitine as an add-on therapy to breast cancer patients maintained on tamoxifen. The objectives of carnitine treatment are diverse: improving tamoxifen-related side effects, offering better cancer prognosis by reducing the risk of developing cancer recurrence or metastasis, and modulating the growth factors which may be, in part, a prospective illustration to overcome tamoxifen resistance. So, it could be recommended to supplement L-carnitine to breast cancer patients starting tamoxifen treatment.

Novel modeling of combinatorial miRNA targeting identifies SNP with potential role in bone density

MicroRNAs (miRNAs) are post-transcriptional regulators that bind to their target mRNAs through base complementarity. Predicting miRNA targets is a challenging task and various studies showed that existing algorithms suffer from high number of false predictions and low to moderate overlap in their predictions. Until recently, very few algorithms considered the dynamic nature of the interactions, including the effect of less specific interactions, the miRNA expression level, and the effect of combinatorial miRNA binding. Addressing these issues can result in a more accurate miRNA:mRNA modeling with many applications, including efficient miRNA-related SNP evaluation. We present a novel thermodynamic model based on the Fermi-Dirac equation that incorporates miRNA expression in the prediction of target occupancy and we show that it improves the performance of two popular single miRNA target finders. Modeling combinatorial miRNA targeting is a natural extension of this model. Two other algorithms show improved prediction efficiency when combinatorial binding models were considered. ComiR (Combinatorial miRNA targeting), a novel algorithm we developed, incorporates the improved predictions of the four target finders into a single probabilistic score using ensemble learning. Combining target scores of multiple miRNAs using ComiR improves predictions over the naïve method for target combination. ComiR scoring scheme can be used for identification of SNPs affecting miRNA binding. As proof of principle, ComiR identified rs17737058 as disruptive to the miR-488-5p:NCOA1 interaction, which we confirmed in vitro. We also found rs17737058 to be significantly associated with decreased bone mineral density (BMD) in two independent cohorts indicating that the miR-488-5p/NCOA1 regulatory axis is likely critical in maintaining BMD in women. With increasing availability of comprehensive high-throughput datasets from patients ComiR is expected to become an essential tool for miRNA-related studies.

Functional characterization of a genetic polymorphism in the promoter of the ESR2 gene

The ESR2 gene encodes the estrogen receptor beta protein. Several studies have shown that genetic variants in the ESR2 gene are associated with a variety of clinical phenotypes. However, very little is known about the functional significance of ESR2 genetic variants. We used a bioinformatics approach to identify regions of the ESR2 promoter that is evolutionarily conserved across the genomes of several species. We resequenced 1.6 kb of the ESR2 gene which included 0.8 kb of the promoter, 0.3 kb of exon ON, and 0.5 kb of the following intron. We identified five single-nucleotide polymorphisms (SNPs) in the ESR2 promoter and one SNP in the intron. Phase analysis indicated that the SNPs likely exist in 11 different haplotypes. Three of the SNPs (rs8008187, rs3829768, rs35036378) were predicted to alter transcription factor binding sites in the ESR2 promoter. All three were detected only in African American subjects. The rs35036378 SNP was in the TATA box and was highly conserved across species. ESR2 promoter reporter assays in LNCaP and SKBR3 cell lines showed that the variant construct containing the rs35036378 SNP allele had approximately 50% less activity relative to the wild-type construct. We conclude that the rs35036378 SNP appears to cause a reduced promoter activity of the ESR2 gene.

Whole genome amplification of DNA for genotyping pharmacogenetics candidate genes

Whole genome amplification (WGA) technologies can be used to amplify genomic DNA when only small amounts of DNA are available. The Multiple Displacement Amplification Phi polymerase based amplification has been shown to accurately amplify DNA for a variety of genotyping assays; however, it has not been tested for genotyping many of the clinically relevant genes important for pharmacogenetic studies, such as the cytochrome P450 genes, that are typically difficult to genotype due to multiple pseudogenes, copy number variations, and high similarity to other related genes. We evaluated whole genome amplified samples for Taqman(™) genotyping of SNPs in a variety of pharmacogenetic genes. In 24 DNA samples from the Coriell human diversity panel, the call rates, and concordance between amplified (∼200-fold amplification) and unamplified samples was 100% for two SNPs in CYP2D6 and one in ESR1. In samples from a breast cancer clinical trial (Trial 1), we compared the genotyping results in samples before and after WGA for three SNPs in CYP2D6, one SNP in CYP2C19, one SNP in CYP19A1, two SNPs in ESR1, and two SNPs in ESR2. The concordance rates were all >97%. Finally, we compared the allele frequencies of 143 SNPs determined in Trial 1 (whole genome amplified DNA) to the allele frequencies determined in unamplified DNA samples from a separate trial (Trial 2) that enrolled a similar population. The call rates and allele frequencies between the two trials were 98 and 99.7%, respectively. We conclude that the whole genome amplified DNA is suitable for Taqman(™) genotyping for a wide variety of pharmacogenetically relevant SNPs.

Glyceollin-elicited soy protein consumption induces distinct transcriptional effects as compared to standard soy protein

Glyceollins are stress-induced compounds in soybeans with bioactive properties distinct from parent soy isoflavones. The goals of this study were to evaluate the effects of dietary glyceollin-enriched and standard soy protein isolates and identify candidate target pathways of glyceollins on transcriptional profiles within mammary gland tissue. Thirty female postmenopausal cynomolgus monkeys were randomized to diets containing one of three protein sources for 3 weeks: (1) control casein/lactalbumin (C/L), (2) standard soy protein containing 194 mg/day isoflavones (SOY), and (3) glyceollin-enriched soy protein containing 189 mg/day isoflavones + 134 mg/day glyceollins (GLY). All diets contained a physiologic dose of estradiol (E2) (1 mg/day). All doses are expressed in human equivalents scaled by caloric intake. Relative to the control C/L diet, the GLY diet resulted in greater numbers of differentially regulated genes, which showed minimal overlap with those of SOY. Effects of GLY related primarily to pathways involved in lipid and carbohydrate metabolism, including peroxisome proliferator-activated receptor (PPAR)-γ and AMP-activated protein kinase (AMPK) signaling, adipocytokine expression, triglyceride synthesis, and lipase activity. Notable genes upregulated by the GLY diet included PPAR-γ, adiponectin, leptin, lipin 1, and lipoprotein lipase. The GLY diet also resulted in lower serum total cholesterol, specifically nonhigh-density lipoprotein cholesterol, and increased serum triglycerides as compared to the C/L diet. No effects of GLY or SOY were seen on serum insulin, adipocytokines, or vascular and bone turnover markers. These preliminary findings suggest that glyceollin-enriched soy protein has divergent effects from standard soy with some specificity for adipocyte activity and nutrient metabolism.

A SNP in steroid receptor coactivator-1 disrupts a GSK3β phosphorylation site and is associated with altered tamoxifen response in bone

The coregulator steroid receptor coactivator (SRC)-1 increases transcriptional activity of the estrogen receptor (ER) in a number of tissues including bone. Mice deficient in SRC-1 are osteopenic and display skeletal resistance to estrogen treatment. SRC-1 is also known to modulate effects of selective ER modulators like tamoxifen. We hypothesized that single nucleotide polymorphisms (SNP) in SRC-1 may impact estrogen and/or tamoxifen action. Because the only nonsynonymous SNP in SRC-1 (rs1804645; P1272S) is located in an activation domain, it was examined for effects on estrogen and tamoxifen action. SRC-1 P1272S showed a decreased ability to coactivate ER compared with wild-type SRC-1 in multiple cell lines. Paradoxically, SRC-1 P1272S had an increased protein half-life. The Pro to Ser change disrupts a putative glycogen synthase 3 (GSK3)β phosphorylation site that was confirmed by in vitro kinase assays. Finally, knockdown of GSK3β increased SRC-1 protein levels, mimicking the loss of phosphorylation at P1272S. These findings are similar to the GSK3β-mediated phospho-ubiquitin clock previously described for the related coregulator SRC-3. To assess the potential clinical significance of this SNP, we examined whether there was an association between SRC-1 P1272S and selective ER modulators response in bone. SRC-1 P1272S was associated with a decrease in hip and lumbar bone mineral density in women receiving tamoxifen treatment, supporting our in vitro findings for decreased ER coactivation. In summary, we have identified a functional genetic variant of SRC-1 with decreased activity, resulting, at least in part, from the loss of a GSK3β phosphorylation site, which was also associated with decreased bone mineral density in tamoxifen-treated women.

Comparison of changes in the lipid profile of postmenopausal women with early stage breast cancer treated with exemestane or letrozole

Effects of aromatase inhibitor (AI) therapy on the plasma lipid profile are not clear. Here the authors describe changes in fasting lipids (total cholesterol, high-density lipoprotein [HDL], low-density lipoprotein [LDL], and triglycerides) before and after 3 months of exemestane or letrozole treatment. HDL was reduced in the entire cohort (P < .001) and in the exemestane group (P < .001) but unchanged in the letrozole group (P = .169). LDL was increased in the entire cohort (P = .005) and in the letrozole group (P = .002) but unchanged in the exemestane group (P = .361). This effect was at least partially attributable to washout of tamoxifen as only patients with prior use of tamoxifen experienced a significant increase in LDL. Baseline HDL was an independent predictor of the change in HDL (r(2) = -0.128, P < .001), and prior tamoxifen use was associated with greater increases in LDL (r(2) = 0.057, P < .001). Use of lipid-altering medications did not protect against the exemestane-induced drop in HDL or the increase in LDL observed in women with prior use of tamoxifen taking letrozole. In conclusion, AI treatment and/or washout of tamoxifen induced detrimental changes in the lipid profile of postmenopausal women with breast cancer.

CYP2D6 genotyping and tamoxifen: an unfinished story in the quest for personalized medicine

The philosophy behind personalized medicine is that each patient has a unique biologic profile that should guide the choice of therapy, resulting in an improved treatment outcome, ideally with reduced toxicity. Thus, there has been increasing interest in identifying genetic variations that are predictive of a drug's efficacy or toxicity. Although it is one of the most effective drugs for treating breast cancer, tamoxifen is not effective in all estrogen receptor (ER)-positive breast cancer patients, and it is frequently associated with side effects, such as hot flashes. Relative resistance to tamoxifen treatment may be a result, in part, from impaired drug activation by cytochrome P450 2D6 (CYP2D6). Indeed, recent studies have identified allelic variations in CYP2D6 to be an important determinant of tamoxifen's activity (and toxicity). This article will summarize the current information regarding the influence of the major genotypes and CYP2D6 inhibitors on tamoxifen metabolism, with a focus on its clinical utility and the current level of evidence for CYP2D6 genotyping of patients who are candidates for tamoxifen treatment.

A review of estrogen receptor alpha gene (ESR1) polymorphisms, mood, and cognition

OBJECTIVE

There are significant individual differences in the extent to which mood and cognition change as a function of reproductive stage, menstrual phase, postpartum, and hormone therapy use. This review explores the extent to which variations or polymorphisms in the estrogen receptor alpha gene (ESR1) predict cognitive and mood outcomes.

METHODS

A literature search was conducted from 1995 to November 2009 through PubMed, Embase, and PsychINFO. Twenty-five manuscripts that summarize investigations of ESR1 in mental health were reviewed.

RESULTS

Among studies investigating ESR1 in relation to cognition, 11 of 14 case-control studies reported an association between ESR1 polymorphisms and risk for developing dementia. Three of four prospective cohort studies reported an association between ESR1 polymorphisms and significant cognitive decline. There are inconsistencies between case-control and cohort studies regarding whether specific ESR1 alleles increase or decrease the risk for cognitive dysfunction. The relationships between ESR1 and cognitive impairment tend to be specific to or driven by women and restricted to risk for Alzheimer disease rather than other dementia causes. Three of five studies examining ESR1 polymorphisms in relation to anxiety or depressive symptoms found significant associations. Significant associations have also been reported between ESR1 polymorphisms and childhood-onset mood disorder and premenstrual dysphoric disorder.

CONCLUSIONS

A strong relationship between ESR1 variants and cognitive outcomes is evident, and preliminary evidence suggests a role of the ESR1 gene in certain mood outcomes. Insights into the discordant results will come from future studies that include haplotype analyses, analyses within specific ethnic/racial populations, and sex-stratified analyses.

Estrogen receptor genotypes, menopausal status, and the effects of tamoxifen on lipid levels: revised and updated results

We previously reported that the ESR1 XbaI genotypes were associated with baseline and tamoxifen-induced serum lipid profiles. The analysis in that study was carried out by PCR followed by restriction-enzyme digestion. After reanalysis using more robust TaqMan assays, the findings related to ~10% of the genotypes for the ESR1 XbaI single-nucleotide polymorphism (SNP) were revised. For the other genotypes (i.e., ESR1 PvuII, ESR2, and CYP2D6), the results were nearly identical to those in the previous study. Upon reanalysis, previously reported associations between the ESR1 Xba1 genotypes and baseline triglyceride and low-density lipoprotein (LDL) cholesterol levels were no longer observed. Previously reported associations between the ESR1 XbaI genotypes and tamoxifen-induced changes in levels of total cholesterol, triglycerides, and high-density lipoprotein (HDL) cholesterol were also no longer observed. However, the following observations from the original report did not change: (i) the levels of circulating lipids are lower in women taking tamoxifen; (ii) there is an association between the ESR2-02 genotypes and changes in triglyceride levels; and (iii) neither ESR1 PvuII nor CYP2D6 is associated with any changes in serum lipid concentrations in patients receiving treatment with tamoxifen.

The Impact of CYP2D6 Genotyping on Tamoxifen Treatment

Tamoxifen remains a cornerstone of treatment for patients with oestrogen-receptor-positive breast cancer. Tamoxifen efficacy depends on the biotransformation, predominantly via the cytochrome P450 2D6 (CYP2D6) isoform, to the active metabolite endoxifen. Both genetic and environmental (drug-induced) factors may alter CYP2D6 enzyme activity directly affecting the concentrations of active tamoxifen metabolites. Several studies suggest that germline genetic variants in CYP2D6 influence the clinical outcomes of patients treated with adjuvant tamoxifen. Here, we review the existing data relating CYP2D6 genotypes to tamoxifen efficacy.

Dietary fat, tamoxifen use and circulating sex hormones in postmenopausal breast cancer survivors

Evidence is inconsistent regarding whether dietary fat influences sex hormone concentrations. This issue is important for breast cancer survivors since clinical recommendations suggest maintaining low hormone levels primarily via pharmacologic agents. This study examines associations between dietary fat and circulating sex hormones among participants in the Health, Eating, Activity and Lifestyle (HEAL) Study, a cohort of breast cancer survivors (N = 511). During a postdiagnosis interview, detailed data were collected on diet, physical activity, lifestyle habits, and medication use (including tamoxifen). Staff measured height and weight and collected fasting bloods. Multivariate linear regression modeled associations of dietary fat with serum sex hormones. Among women using tamoxifen, we observed modest inverse associations of dietary fat with estrone (P < 0.01), estradiol (P < 0.05), testosterone (P < 0.01), free testosterone (P < 0.01), and DHEA (P < 0.01) for higher vs. lower fat intake; but there was no evidence for a trend. Associations were consistent across measures (percent energy from fat, total, saturated, and polyunsaturated fat), and modest effect modification was observed between fat intake and tamoxifen in relation to hormones. Among women not using tamoxifen, fat intake was not associated with hormone concentrations. Further work is needed to confirm the findings and to understand the clinical implications of these observations.

Influence of red clover (Trifolium pratense) isoflavones on gene and protein expression profiles in liver of ovariectomized rats

Isoflavones such as genistein, biochanin A, formononetin, and glycetin are fairly abundant in red clover (Trifolium pratense, Fabaceae) and show estrogenic, antioxidant and hypolipidemic activities. To explore these effects mediated by red clover extract at the gene and protein levels, female ovariectomized rats were treated with an isoflavone rich extract of T. pratense. The experimental rats were divided into 2 groups of five animals each: a) control b) experimental group (red clover extract treated with 450mg/kg/day for four days). The treatment influenced the plasma lipid levels differentially. Plasma LDL concentrations were significantly reduced (p<0.05), whereas triglycerides increased (p<0.05). Plasma HDL and total cholesterol remained unchanged. The rat livers were examined for their differential gene expression by Affymetrix Rae230 DNA microarrays. In addition, the total liver proteins were separated by 2D PAGE and proteins, which showed differences in their intensities were identified by MALDI-TOF-MS. The extract influenced the transcript levels of many novel estrogen and non-estrogen responsive genes as well as other regulatory genes. Functional annotations indicate that genes involved in metabolic pathways, information processing, membrane transport regulation, signal transduction and other cellular processes were regulated. Quantitative reverse transcription analysis with real-time PCR confirmed that red clover extract regulates genes involved in lipid metabolism and antioxidation mechanisms. Proteomic analysis support the potential of red clover extract to modulate the lipid metabolism. In summary isoflavone rich red clover extract mediates numerous genomic and non-genomic effects, which influence besides the lipid metabolism a broad range of cellular functions, including metabolic actions, cell cycle regulation and antioxidant activity.

Thresholds for therapies: highlights of the St Gallen International Expert Consensus on the primary therapy of early breast cancer 2009

The 11(th) St Gallen (Switzerland) expert consensus meeting on the primary treatment of early breast cancer in March 2009 maintained an emphasis on targeting adjuvant systemic therapies according to subgroups defined by predictive markers. Any positive level of estrogen receptor (ER) expression is considered sufficient to justify the use of endocrine adjuvant therapy in almost all patients. Overexpression or amplification of HER2 by standard criteria is an indication for anti-HER2 therapy for all but the very lowest risk invasive tumours. The corollary is that ER and HER2 must be reliably and accurately measured. Indications for cytotoxic adjuvant therapy were refined, acknowledging the role of risk factors with the caveat that risk per se is not a target. Proliferation markers, including those identified in multigene array analyses, were recognised as important in this regard. The threshold for indication of each systemic treatment modality thus depends on different criteria which have been separately listed to clarify the therapeutic decision-making algorithm.

CYP2D6 and tamoxifen: DNA matters in breast cancer

Tamoxifen is the most widely used anti-oestrogen for the treatment of hormone-dependent breast cancer. The pharmacological activity of tamoxifen is dependent on its conversion by the hepatic drug-metabolizing enzyme cytochrome P450 2D6 (CYP2D6) to its abundant metabolite, endoxifen. Patients with reduced CYP2D6 activity, as a result of either their genotype or induction by the co-administration of drugs that inhibit CYP2D6 function, produce little endoxifen and seem to derive inferior therapeutic benefit from tamoxifen. Here we review the existing data that relate CYP2D6 genotypes to response to tamoxifen and discuss whether the analysis of the CYP2D6 genotype might be an early example of a pharmacogenetic tool for optimizing breast cancer therapy.

Estrogen receptor genotype is associated with risk of venous thromboembolism during tamoxifen therapy

Thromboembolism is a serious complication of tamoxifen therapy in women with breast cancer. Banked DNA from tamoxifen-treated individuals with breast cancer from the Marshfield Clinic Personalized Medicine Research Project, a population-based DNA repository, was tested for association between incidence of tamoxifen-associated thromboembolic events (TTE) and single nucleotide polymorphisms encoding the estrogen receptors 1,2 (ESR1, ESR2) or drug metabolism enzymes cytochrome P450 2D6 (CYP2D6) and aromatase (CYP19). TTE were experienced by 16/220 subjects with risk association noted for XbaI (rs9340799) genotype and ESR1 Xbal/PvuII diplotype (rs9340799 and rs2234693) (hazard ratio 3.47, 95% CI 0.97-12.44, P = 0.035). Association persisted after adjusting for classical risk factors including age at diagnosis and body mass index at enrollment. Initial evidence of association between increased risk for TTE and ESR1 genotype and ESR1 diplotype is presented. Determination of estrogen receptor genotype may identify a subset of women at increased risk for thromboembolism with tamoxifen exposure.

Do Estrogen Receptor beta Polymorphisms Play A Role in the Pharmacogenetics of Estrogen Signaling?

Estrogen hormones play critical roles in the regulation of many tissue functions. The effects of estrogens are primarily mediated by the estrogen receptors (ER) alpha and beta. ERs are ligand-activated transcription factors that regulate a complex array of genomic events that orchestrate cellular growth, differentiation and death. Although many factors contribute to their etiology, estrogens are thought to be the primary agents for the development and/or progression of target tissue malignancies. Many of the current modalities for the treatment of estrogen target tissue malignancies are based on agents with diverse pharmacology that alter or prevent ER functions by acting as estrogen competitors. Although these compounds have been successfully used in clinical settings, the efficacy of treatment shows variability. An increasing body of evidence implicates ERalpha polymorphisms as one of the contributory factors for differential responses to estrogen competitors. This review aims to highlight the recent findings on polymorphisms of the lately identified ERbeta in order to provide a functional perspective with potential pharmacogenomic implications.

Pharmacogenetics and breast cancer endocrine therapy: CYP2D6 as a predictive factor for tamoxifen metabolism and drug response?

The identification of genetic polymorphisms that influence the efficacy and safety of therapies for breast cancer may allow future treatments to be individualised based not only on tumour characteristics but also on host genetics. Genetic factors that affect the metabolism, efficacy and safety of tamoxifen, one of the most common drugs used for the treatment and prevention of breast cancer, have received particular attention. Cytochrome P450 2D6 (CYP2D6) is crucial in the metabolism of tamoxifen to its active metabolite endoxifen. Women with genetic variants of CYP2D6 or who take drugs that inhibit the enzyme have low endoxifen plasma concentrations and may show reduced benefits to tamoxifen treatment. CYP2D6 polymorphisms and variants in other candidate genes may also influence secondary benefits and side effects of tamoxifen. Here, we summarise data suggesting that CYP2D6 status may be an important predictor of the benefits of tamoxifen to an individual; in addition, we briefly discuss the role of variants in other candidate genes. Whether CYP2D6 status should be determined prior to initiating tamoxifen therapy is currently under debate and may be appropriate only for select women who are candidates for tamoxifen alone but for whom alternative standard options are available.

Estrogen receptor genotypes influence hot flash prevalence and composite score before and after tamoxifen therapy

PURPOSE

Hot flashes are common and frequently lead to drug discontinuation among women prescribed tamoxifen. We determined whether genetic polymorphisms in estrogen receptors (ESRs) alpha and beta (ESR1 and ESR2, respectively) are associated with tamoxifen-induced hot flashes.

PATIENTS AND METHODS

We determined ESR1 PvuII and XbaI and ESR2-02 genotypes in 297 women who were initiating tamoxifen. One-week hot flash diaries were collected to calculate a hot flash score (frequency x severity) before and 1, 4, 8, and 12 months after starting tamoxifen.

RESULTS

Approximately 80% of 297 participants reported hot flashes before or during the first year of tamoxifen. After 4 months of tamoxifen, premenopausal women who did not receive adjuvant chemotherapy had a four-fold increase in hot flash score (from 5.9 to 23.6; P = .003) compared with a 1.17-fold increase (from 19.6 to 23; P = .34) in those who received chemotherapy. In premenopausal women, increased number of ESR1 PvuII and XbaI CG alleles was associated with higher baseline hot flash scores compared with those who had other haplotypes (P = .0026). At 4 months, postmenopausal women with ESR1 PvuII CC and ESR2-02 GG genotypes had 4.6 times increases in hot flash scores than other postmenopausal women (56 v 12; P = .0007). Women who had the ESR2-02 AA genotype were significantly less likely to experience tamoxifen-induced hot flashes than women who carried at least one ESR-02 G allele (hazard ratio, 0.26; 95% CI, 0.10 to 0.63; P = .001).

CONCLUSION

Knowledge of menopausal status, prior chemotherapy, and ESR genotype may help predict which women are most likely to suffer hot flashes during tamoxifen treatment.