Epigenetics refers to alterations in gene expression due to modifications in histone acetylation and DNA methylation at the promoter regions of genes. Unlike genetic mutations, epigenetic alterations ...are not due to modifications in the gene primary nucleotide sequence. The importance of epigenetics in the initiation and progression of breast cancer has led many investigators to incorporate this novel and exciting field in breast cancer drug development. Several drugs that target epigenetic alterations, including inhibitors of histone deacetylase (HDAC) and DNA methyltransferase (DNMT), are currently approved for treatment of hematological malignancies and are available for clinical investigation in solid tumors. In this manuscript, we review the critical role of epigenetics in breast cancer including the potential for epigenetic alterations to serve as biomarkers determining breast cancer prognosis and response to therapy. We highlight initial promising results to date with use of epigenetic modifiers in patients with breast cancer and the ongoing challenges involved in the successful establishment of these agents for the treatment of breast cancer.
Aromatase inhibitors are somewhat more effective than tamoxifen as adjuvant therapy in postmenopausal women with early breast cancer. This benefit was extended to premenopausal women when they also ...received ovarian suppression to prevent ovarian compensation for aromatase inhibition.
The most effective adjuvant endocrine therapy for premenopausal women with hormone-receptor (estrogen, progesterone, or both)–positive breast cancer is uncertain. Tamoxifen for at least 5 years is a standard of care.
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Adjuvant suppression of ovarian function (hereafter, ovarian suppression) may be recommended in addition. For postmenopausal women, adjuvant therapy with an aromatase inhibitor, as compared with tamoxifen, improves outcomes.
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In 2003, the International Breast Cancer Study Group (IBCSG) initiated two randomized, phase 3 trials, the Tamoxifen and Exemestane Trial (TEXT) and the Suppression of Ovarian Function Trial (SOFT), involving premenopausal women with hormone-receptor–positive early breast cancer, through collaboration with . . .
Adjuvant tamoxifen therapy substantially decreases the risk of recurrence and mortality in women with hormone (estrogen and/or progesterone) receptor-positive breast cancer. Previous studies have ...suggested that metabolic conversion of tamoxifen to endoxifen by cytochrome P450 2D6 (CYP2D6) is required for patient benefit from tamoxifen therapy.
Tumor specimens from a subset of postmenopausal patients with hormone receptor-positive early-stage (stages I, II, and IIIA) breast cancer, who were enrolled in the randomized double-blind Arimidex, Tamoxifen, Alone or in Combination (ATAC) clinical trial, were genotyped for variants in CYP2D6 (N = 1203 patients: anastrozole trade name: Arimidex group, n = 615 patients; tamoxifen group, n = 588 patients) and UDP-glucuronosyltransferase-2B7 (UGT2B7), whose gene product inactivates endoxifen (N = 1209 patients; anastrozole group, n = 606 patients; tamoxifen group, n = 603 patients). Genotyping was performed using polymerase chain reaction-based TaqMan assays. Based on the genotypes for CYP2D6, patients were classified as poor metabolizer (PM), intermediate metabolizer (IM), or extensive metabolizer (EM) phenotypes. We evaluated the association of CYP2D6 and UGT2B7 genotype with distant recurrence (primary endpoint) and any recurrence (secondary endpoint) by estimating the hazard ratios (HRs) and corresponding 95% confidence intervals (CIs) using Cox proportional hazards models. All statistical tests were two-sided.
After a median follow-up of 10 years, no statistically significant associations were observed between CYP2D6 genotype and recurrence in tamoxifen-treated patients (PM vs EM: HR for distant recurrence = 1.25, 95% CI = 0.55 to 3.15, P = .64; HR for any recurrence = 0.99, 95% CI = 0.48 to 2.08, P = .99). A near-null association was observed between UGT2B7 genotype and recurrence in tamoxifen-treated patients. No associations were observed between CYP2D6 and UGT2B7 genotypes and recurrence in anastrozole-treated patients.
The results do not support the hypothesis that CYP2D6 genotype predicts clinical benefit of adjuvant tamoxifen treatment among postmenopausal breast cancer patients.
Aromatase inhibitors are widely used as adjuvant therapy in postmenopausal women with hormone receptor-positive breast cancer. While the agents are associated with slightly improved survival outcomes ...when compared to tamoxifen alone, bone and musculoskeletal side effects are substantial and often lead to discontinuation of therapy. Ideally, the symptoms should be prevented or adequately treated. This review will focus on bone and musculoskeletal side effects of aromatase inhibitors, including osteoporosis, fractures, and arthralgias. Recent advances have been made in identifying potential mechanisms underlying these effects. Adequate management of symptoms may enhance patient adherence to therapy, thereby improving breast cancer-related outcomes.
Aromatase inhibitors (AIs) are effective for treatment of hormone receptor-positive breast cancer, but adherence and persistence with therapy are poor. Predictors of treatment discontinuation are not ...clearly defined. It is unknown whether patients with intolerable toxicity from one AI are able to tolerate another.
Women with early-stage breast cancer initiating AI therapy were enrolled onto a multicenter, prospective, open-label randomized trial of exemestane versus letrozole. Patients completed symptom questionnaires at baseline and serially during therapy. Patients who developed AI-associated intolerable symptoms and discontinued treatment were given the option to switch to the other study AI after a 2- to 8-week washout period.
Of the 503 enrolled women, 32.4% discontinued initial AI therapy within 2 years because of adverse effects; 24.3% discontinued specifically because of musculoskeletal symptoms. Median time to treatment discontinuation as a result of any symptom was 6.1 months (range, 0.1 to 21.2 months) and was significantly shorter in patients randomly assigned to exemestane (hazard ratio HR, 1.5; 95% CI, 1.1 to 2.1; P = .02). Younger age and taxane-based chemotherapy were associated with higher likelihood of treatment discontinuation (HR, 1.4; 95% CI, 1.02 to 1.9; P = .04; and HR, 1.9; 95% CI, 1.00 to 3.6; P = .048, respectively). Of the 83 patients who chose to switch to the second AI, 38.6% continued the alternate AI for a median of 13.7 months.
Premature discontinuation of initial AI therapy as a result of symptoms is common, although more than one third of patients may be able to tolerate a different AI medication. Additional research is needed to identify predictive tools and interventions for AI-associated treatment-emergent symptoms.
In breast cancer models, combination epigenetic therapy with a DNA methyltransferase inhibitor and a histone deacetylase inhibitor led to reexpression of genes encoding important therapeutic targets, ...including the estrogen receptor (ER). We conducted a multicenter phase II study of 5-azacitidine and entinostat in women with advanced hormone-resistant or triple-negative breast cancer (TNBC).
Patients received 5-azacitidine 40 mg/m
(days 1-5, 8-10) and entinostat 7 mg (days 3, 10) on a 28-day cycle. Continuation of epigenetic therapy was offered with the addition of endocrine therapy at the time of progression optional continuation (OC) phase. Primary endpoint was objective response rate (ORR) in each cohort. We hypothesized that ORR would be ≥20% against null of 5% using Simon two-stage design. At least one response was required in 1 of 13 patients per cohort to continue accrual to 27 per cohort (type I error, 4%; power, 90%).
There was one partial response among 27 women with hormone-resistant disease (ORR = 4%; 95% CI, 0-19), and none in 13 women with TNBC. One additional partial response was observed in the OC phase in the hormone-resistant cohort (
= 12). Mandatory tumor samples were obtained pre- and posttreatment (58% paired) with either up- or downregulation of ER observed in approximately 50% of posttreatment biopsies in the hormone-resistant, but not TNBC cohort.
Combination epigenetic therapy was well tolerated, but our primary endpoint was not met. OC phase results suggest that some women benefit from epigenetic therapy and/or reintroduction of endocrine therapy beyond progression, but further study is needed.
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To develop evidence-based guidelines, based on a systematic review, for endocrine therapy for postmenopausal women with hormone receptor-positive breast cancer.
A literature search identified ...relevant randomized trials. Databases searched included MEDLINE, PREMEDLINE, the Cochrane Collaboration Library, and those for the Annual Meetings of the American Society of Clinical Oncology (ASCO) and the San Antonio Breast Cancer Symposium (SABCS). The primary outcomes of interest were disease-free survival, overall survival, and time to contralateral breast cancer. Secondary outcomes included adverse events and quality of life. An expert panel reviewed the literature, especially 12 major trials, and developed updated recommendations.
An adjuvant treatment strategy incorporating an aromatase inhibitor (AI) as primary (initial endocrine therapy), sequential (using both tamoxifen and an AI in either order), or extended (AI after 5 years of tamoxifen) therapy reduces the risk of breast cancer recurrence compared with 5 years of tamoxifen alone. Data suggest that including an AI as primary monotherapy or as sequential treatment after 2 to 3 years of tamoxifen yields similar outcomes. Tamoxifen and AIs differ in their adverse effect profiles, and these differences may inform treatment preferences.
The Update Committee recommends that postmenopausal women with hormone receptor-positive breast cancer consider incorporating AI therapy at some point during adjuvant treatment, either as up-front therapy or as sequential treatment after tamoxifen. The optimal timing and duration of endocrine treatment remain unresolved. The Update Committee supports careful consideration of adverse effect profiles and patient preferences in deciding whether and when to incorporate AI therapy.
Reversal of promoter DNA hypermethylation and associated gene silencing is an attractive cancer therapy approach. The DNA methylation inhibitors decitabine and azacitidine are efficacious for ...hematological neoplasms at lower, less toxic, doses. Experimentally, high doses induce rapid DNA damage and cytotoxicity, which do not explain the prolonged time to response observed in patients. We show that transient exposure of cultured and primary leukemic and epithelial tumor cells to clinically relevant nanomolar doses, without causing immediate cytotoxicity, produce an antitumor “memory” response, including inhibition of subpopulations of cancer stem-like cells. These effects are accompanied by sustained decreases in genomewide promoter DNA methylation, gene reexpression, and antitumor changes in key cellular regulatory pathways. Low-dose decitabine and azacitidine may have broad applicability for cancer management.
► Transient DAC or AZA sustains antitumor responses and reduces self-renewal ► Acute cytotoxicity does not appear to account for the lasting effects of the drugs ► Low-dose DAC causes sustained global DNA demethylation and gene reexpression ► Low-dose DAC or AZA sustains antitumor responses through key signaling pathways
Purpose
Delays in initiating adjuvant endocrine therapy (AET) are a cause for concern among women with breast cancer and clinicians, but the impact of delayed AET on overall survival (OS) is unclear. ...This study seeks to describe the relationship between delayed AET and OS.
Methods
Retrospective cohort study of women with stage II and III hormone receptor positive, human epidermal receptor 2 negative, invasive breast cancer, identified from the National Cancer Database. The primary exposure delayed AET, was defined as initiation of AET more than 12 months after breast cancer diagnosis. Using logistic regression, we examined predictors of delayed AET. The survival analysis with Cox proportional hazards regression adjusted for patient, tumor, and treatment characteristics.
Results
Among the 391,594 included women, 12,162 (3.1%) had delayed AET. Predictors of delayed AET included Black race (adjusted odds ratio aOR = 1.61, 95% confidence interval CI 1.52–1.70) or Hispanic ethnicity (aOR = 1.25, 95% CI 1.16–1.35) vs white race, Medicare (aOR = 1.13, 95% CI 1.06–1.20) or Medicaid (aOR = 1.41, 95% CI 1.32–1.50) versus private insurance, and cancer stage III (aOR = 1.24, 95% CI 1.19–1.30) vs stage II. With median follow-up of 67.4 months, 67,335 (17.2%) patients died. Delayed AET had no statistically significant effect on the hazard of death (adjusted hazards ratio = 1.01; 95% CI 0.96–1.06) compared to initiation within 12 months of diagnosis.
Conclusion
This study suggests that there may be no adverse impact on survival if initiation of AET occurs 12 to 24 months after initial diagnosis compared to within 12 months of diagnosis as currently recommended.
Epigenetic therapy is emerging as a potential therapy for solid tumors. To investigate its mechanism of action, we performed integrative expression and methylation analysis of 63 cancer cell lines ...(breast, colorectal, and ovarian) after treatment with the DNA methyltransferase inhibitor 5-azacitidine (AZA). Gene Set Enrichment Analysis demonstrated significant enrichment for immunomodulatory pathways in all three cancers (14.4-31.3%) including interferon signaling, antigen processing and presentation, and cytokines/chemokines. Strong upregulation of cancer testis antigens was also observed. An AZA IMmune gene set (AIMs) derived from the union of these immunomodulatory pathway genes classified primary tumors from all three types, into "high" and "low" AIM gene expression subsets in tumor expression data from both TCGA and GEO. Samples from selected patient biopsies showed upregulation of AIM genes after treatment with epigenetic therapy. These results point to a broad immune stimulatory role for DNA demethylating drugs in multiple cancers.
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