Years Of Tamoxifen Treatment Research Articles

Genomic alterations identified by array comparative genomic hybridization as prognostic markers in tamoxifen-treated estrogen receptor-positive breast cancer

BackgroundA considerable proportion of estrogen receptor (ER)-positive breast cancer recurs despite tamoxifen treatment, which is a serious problem commonly encountered in clinical practice. We tried to find novel prognostic markers in this subtype of breast cancer.MethodsWe performed array comparative genomic hybridization (CGH) with 1,440 human bacterial artificial chromosome (BAC) clones to assess copy number changes in 28 fresh-frozen ER-positive breast cancer tissues. All of the patients included had received at least 1 year of tamoxifen treatment. Nine patients had distant recurrence within 5 years (Recurrence group) of diagnosis and 19 patients were alive without disease at least 5 years after diagnosis (Non-recurrence group).ResultsPotential prognostic variables were comparable between the two groups. In an unsupervised clustering analysis, samples from each group were well separated. The most common regions of gain in all samples were 1q32.1, 17q23.3, 8q24.11, 17q12-q21.1, and 8p11.21, and the most common regions of loss were 6q14.1-q16.3, 11q21-q24.3, and 13q13.2-q14.3, as called by CGH-Explorer software. The average frequency of copy number changes was similar between the two groups. The most significant chromosomal alterations found more often in the Recurrence group using two different statistical methods were loss of 11p15.5-p15.4, 1p36.33, 11q13.1, and 11p11.2 (adjusted p values <0.001). In subgroup analysis according to lymph node status, loss of 11p15 and 1p36 were found more often in Recurrence group with borderline significance within the lymph node positive patients (adjusted p = 0.052).ConclusionOur array CGH analysis with BAC clones could detect various genomic alterations in ER-positive breast cancers, and Recurrence group samples showed a significantly different pattern of DNA copy number changes than did Non-recurrence group samples.

The Use of Early Adjuvant Aromatase Inhibitor Therapy: Contributions From the BIG 1-98 Letrozole Trial

Letrozole has proven efficacious in a variety of therapeutic scenarios, including that of extended adjuvant therapy following 5 years of tamoxifen treatment in postmenopausal women with estrogen-receptor-positive early breast cancer. The Breast International Group 1-98 trial (BIG 1-98) is the first to study the efficacy of upfront letrozole treatment and the first to evaluate the benefits of initial versus sequential aromatase inhibitor therapy. At 25.8 months of follow-up, the primary core analysis of BIG 1-98 compared the efficacy of upfront letrozole treatment with that of upfront tamoxifen treatment in 8,010 postmenopausal women with early breast cancer. The primary endpoint was disease-free survival (DFS). Secondary endpoints included overall survival, distant DFS, systemic DFS, and safety. Letrozole significantly increased DFS, reduced distant recurrences, and prolonged time to distant metastasis compared with tamoxifen. The advantage for letrozole was particularly evident in women at increased risk of recurrence (node-positive and/or chemotherapy treated). Compared with tamoxifen, postmenopausal women receiving letrozole treatment experienced less venous thromboembolic and endometrial events, but more skeletal and grade 3-5 cardiac events, although the frequencies of these latter events were relatively low in both arms (2.1% v 1.1%). There were more deaths from noncancer causes in the letrozole group, but the numbers were small and, overall, there were 14% fewer deaths among patients in the letrozole group. Letrozole has an efficacy advantage over tamoxifen and can now be considered part of standard adjuvant therapy for postmenopausal women with endocrine-responsive breast cancer. Women at increased risk for recurrence may obtain protective benefit from letrozole. Letrozole is generally well tolerated and is associated with a similar frequency of serious side effects, but fewer deaths, than tamoxifen.

Adjuvant Endocrine Therapy for Postmenopausal Women with Early Breast Cancer

Results from multiple clinical trials involving aromatase inhibitors have added to the knowledge base relating to endocrine therapy of postmenopausal women with hormone receptor-positive early breast cancer. In the extended adjuvant setting, data from the Austrian Breast and Colorectal Cancer Study Group 6a trial showed an advantage for anastrozole following 5 years of tamoxifen treatment, consistent with the more robust MA.17 trial that examined letrozole versus placebo following 5 years of tamoxifen treatment. The combined analysis of the Austrian Breast and Colorectal Cancer Study Group 8 trial and the German Arimidex Nolvadex 95 trial, plus the Italian Tamoxifen Anastrozole trial, have shown the advantage of switching to anastrozole over continuing the tamoxifen to complete the full 5 years of adjuvant therapy. These trials support the previously reported larger and double-blind Intergroup Exemestane Study. The Arimidex, Tamoxifen, Alone or in Combination trial now has data out to 68 months of median follow-up showing the maintenance of a significant advantage of anastrozole over tamoxifen for disease-free survival. In this initial treatment setting, the Breast International Group 1-98 trial recently showed a significant advantage for letrozole over tamoxifen. The current debate is centered on whether the optimal strategy is to give an aromatase inhibitor initially or after several years of tamoxifen treatment. Multiple important questions remain, including the predictive value of molecular markers such as progesterone receptor, the optimal duration of aromatase inhibitor therapy, the long-term adverse effects, and the relative efficacy and toxicity of the different aromatase inhibitors.

Optimizing the use of aromatase inhibitors in adjuvant therapy for postmenopausal patients with hormone-responsive early breast cancer: current and future prospects

Five years of tamoxifen treatment after primary surgery has had a significant impact on outcomes for women with early breast cancer, but the third-generation aromatase inhibitors (AIs) are now challenging tamoxifen as the gold standard endocrine adjuvant treatment. Results from two large, phase III, early adjuvant studies have indicated that the AIs letrozole and anastrozole offer greater protection against recurrence than tamoxifen in upfront substitution strategies in the first 5 years after surgery. Similarly, changeover to an AI (exemestane or anastrozole) after 2-3 years of tamoxifen has been shown to offer greater protection against recurrence than 5 years of tamoxifen. More than 50% of early breast cancer recurrences occur five or more years after surgery. Letrozole has been shown to offer greater protection against recurrence than placebo in the 5 years after a standard course of tamoxifen. The safety implications of treatment with these potent AIs for 5 years or more are being closely monitored. Anticipated effects of estrogen deprivation on bone health may be treatable with bisphosphonates, and this strategy is under investigation. Effects on the cardiovascular system, and other estrogen-sensitive systems such as the central nervous system, are currently unclear and further results are awaited. Current evidence indicates that the third-generation AIs will improve outcomes for many women with early breast cancer.

Adjuvant endocrine therapy in postmenopausal breast cancer patients

Tamoxifen has been the endocrine agent of choice for adjuvant hormonal therapy for early breast cancer since approval in 1986. Five years of tamoxifen treatment produced a significant reduction in recurrence and death over more than 10 years of follow-up in women with estrogen receptor-positive (ER+) breast cancer. In large randomised trials, the standard of 5 years tamoxifen has been challenged by third-generation aromatase inhibitors (AIs) in the adjuvant setting. This review provides a synopsis of the most recent trial results and a discussion of remaining areas of uncertainties. Although currently tamoxifen still remains a valid option, increasing evidence from the new AI adjuvant trials suggests that optimised adjuvant endocrine treatment should incorporate an AI either as initial or as sequential therapy.

Randomized Trial of Letrozole Following Tamoxifen as Extended Adjuvant Therapy in Receptor-Positive Breast Cancer: Updated Findings from NCIC CTG MA.17

Most recurrences in women with breast cancer receiving 5 years of adjuvant tamoxifen occur after 5 years. The MA.17 trial, which was designed to determine whether extended adjuvant therapy with the aromatase inhibitor letrozole after tamoxifen reduces the risk of such late recurrences, was stopped early after an interim analysis showed that letrozole improved disease-free survival. This report presents updated findings from the trial. Postmenopausal women completing 5 years of tamoxifen treatment were randomly assigned to a planned 5 years of letrozole (n = 2593) or placebo (n = 2594). The primary endpoint was disease-free survival (DFS); secondary endpoints included distant disease-free survival, overall survival, incidence of contralateral tumors, and toxic effects. Survival was examined using Kaplan-Meier analysis and log-rank tests. Planned subgroup analyses included those by axillary lymph node status. All statistical tests were two-sided. After a median follow-up of 30 months (range = 1.5-61.4 months), women in the letrozole arm had statistically significantly better DFS and distant DFS than women in the placebo arm (DFS: hazard ratio [HR] for recurrence or contralateral breast cancer = 0.58, 95% confidence interval [CI] = 0.45 to 0.76; P < .001; distant DFS: HR = 0.60, 95% CI = 0.43 to 0.84; P = .002). Overall survival was the same in both arms (HR for death from any cause = 0.82, 95% CI = 0.57 to 1.19; P = .3). However, among lymph node-positive patients, overall survival was statistically significantly improved with letrozole (HR = 0.61, 95% CI = 0.38 to 0.98; P = .04). The incidence of contralateral breast cancer was lower in women receiving letrozole, but the difference was not statistically significant. Women receiving letrozole experienced more hormonally related side effects than those receiving placebo, but the incidences of bone fractures and cardiovascular events were the same. Letrozole after tamoxifen is well-tolerated and improves both disease-free and distant disease-free survival but not overall survival, except in node-positive patients.

Changes on Bone Mineral Density after Adjuvant Treatment in Women with Non-metastatic Breast Cancer

. Adjuvant therapies have prolonged survival of non-metastatic breast cancer (NMBC) patients, but they also decrease bone mineral density (BMD). We have analyzed the effects of chemotherapy, hormone therapy with tamoxifen or both, on BMD of women with NMBC. We prospectively included 168 women with NMBC (stage I-III) referred to the Medical Oncology Service of University Hospital of Canary Islands between 1997 and 2001 (55 +/- 12 years; 37% premenopausal; 43 +/- 13 months of follow-up). We measured lumbar and hip BMD (g/cm2) at diagnosis, after chemotherapy and after 12 months of tamoxifen. If a low BMD was detected, women were treated with bisphosphonates. BMD after chemotherapy (n = 83) significantly decreased at lumbar (1.014 +/- 0; 0.995 +/- 0, p = 0.0001), trochanter (0.701 +/- 0; 0.690 +/- 0, p = 0.001), intertrochanter (1.095 +/- 0; 1.078 +/- 0, p = 0.0001) and total hip (0.924 +/- 0; 0.915 +/- 0, p = 0.046) areas. Although 60% of the premenopausal women suffered amenorrhea after chemotherapy, there were not significant differences in BMD between them and women who retained menses. BMD of women who received 12 months of tamoxifen after chemotherapy increased--total hip (0.907 +/- 0; 0.922 +/- 0, p = 0.005) and intertrochanter (1.071 +/- 0; 1.091 +/- 0, p = 0.003)--or remained stable--lumbar, femoral neck, trochanter, and Ward's triangle (n = 39). When tamoxifen was the only adjuvant treatment, BMD after 12 months (n = 22) increased in trochanter area (0.644 +/- 0; 0.663 +/- 0, p = 0.011), and remained stable in all other sites. 50 (30%) patients were treated with bisphosphonates because of osteopenia. Women with NMBC are affected by early bone loss after adjuvant chemotherapy. This bone loss is attenuated by one year of tamoxifen treatment.

Switching to Anastrozole Versus Continued Tamoxifen Treatment of Early Breast Cancer: Preliminary Results of the Italian Tamoxifen Anastrozole Trial

Tamoxifen, which is actually the gold standard adjuvant treatment in estrogen receptor-positive early breast cancer, is associated with an increased risk of endometrial cancer and other life-threatening events. Moreover, many women relapse during or after tamoxifen therapy because of the development of resistance. Therefore new approaches are required. We conducted a prospective randomized trial to test the efficacy of switching postmenopausal patients who were already receiving tamoxifen to the aromatase inhibitor anastrozole. After 2 to 3 years of tamoxifen treatment, patients were randomly assigned either to receive anastrozole 1 mg/d or to continue receiving tamoxifen 20 mg/d, for a total duration of treatment of 5 years. Disease-free survival was the primary end point. Event-free survival, overall survival, and safety were secondary end points. Four hundred forty-eight patients were enrolled. All women had node-positive, estrogen receptor-positive tumors. At a median follow-up time of 36 months, 45 events had been reported in the tamoxifen group compared with 17 events in the anastrozole group (P = .0002). Disease-free and local recurrence-free survival were also significantly longer in the anastrozole group (hazard ratio [HR] = 0.35; 95% CI, 0.18 to 0.68; P = .001 and HR = 0.15; 95% CI, 0.03 to 0.65; P = .003, respectively). Overall, more adverse events were recorded in the anastrozole group compared with the tamoxifen group (203 v 150, respectively; P = .04). However, more events were life threatening or required hospitalization in the tamoxifen group than in the anastrozole group (33 of 150 events v 28 of 203 events, P = .04). Switching to anastrozole after the first 2 to 3 years of treatment is well tolerated and significantly improves event-free and recurrence-free survival in postmenopausal patients with early breast cancer.

Can Molecular Markers Predict When to Implement Treatment with Aromatase Inhibitors in Invasive Breast Cancer?

Resistance to tamoxifen is linked to overexpression of HER2, and aromatase inhibitors show particular benefit in progesterone receptor (PR)-negative patients. We previously reported reduced survival in patients overexpressing HER1, HER2, and HER3. We now show that both HER1-3 and PR status predicts for early relapse in estrogen receptor (ER)-positive tamoxifen-treated breast cancer patients. Tissue microarray technology was used to analyze 402 ER-positive tamoxifen-treated patients. Immunohistochemistry using epidermal growth factor receptor, HER2, HER3, HER4, and PR antibodies was done. Kaplan-Meier life table and Cox Regression analysis (log-rank testing of differences in breast cancer-related relapse on tamoxifen) was done. HER1-3 (but not HER4) overexpression predicted for early relapse on tamoxifen (P = 0.0060). PR-negative cases were also significantly more likely to relapse while on tamoxifen (P= 0.017). HER1-3-positive and/or PR-negative patients combined as a "high-risk" group were significantly more likely to relapse on tamoxifen in univariate (P < 0.0001) and Cox's multivariate analysis (P = 0.0069). However, this applied to early relapse on tamoxifen only, as any disease relapse after 3 years of tamoxifen was unrelated to PR/HER status. We show that HER1-3 and PR status can identify time-dependent de novo tamoxifen resistance with risk declining markedly after 3 years of tamoxifen treatment. These results parallel data from the ATAC and Intergroup Exemastane Study trials which suggest that whereas PR-negative patients derive greater benefit from initial aromatase inhibitor treatment, PR status has no effect on response when given as delayed treatment to those disease free on tamoxifen after 3 years.

Two years of adjuvant tamoxifen in premenopausal patients with breast cancer: a randomised, controlled trial with long-term follow-up

Adjuvant tamoxifen treatment increases recurrence-free survival (RFS) and overall survival (OS) in early breast cancer, although in premenopausal patients the number of studies comparing tamoxifen vs no treatment are limited. We report herein the effect on RFS of adjuvant tamoxifen treatment in a multicentre trial of premenopausal patients with stage II breast cancer patients randomised between 1986 and 1991 to 2 years of tamoxifen treatment ( n = 276) or no treatment ( n = 288). The receptor status of the tumour was known for 541 (96%) of the patients included. Tamoxifen treatment significantly increased RFS in patients with hormone receptor-positive (oestrogen receptor-positive (ER+) and/or progesterone receptor-positive (PR+)) tumours (Relative Risk (RR) 0.65; 95% Confidence Interval (CI): 0.48–0.89, P = 0.006), and the beneficial effect of tamoxifen was extended to patients with indicators of poor prognosis, such as young age and nodal-positivity. PR status was a significant predictor of response to tamoxifen in multivariate models with testing of interactions of hormone receptor status and adjuvant therapy.

Should tamoxifen be used in breast cancer prevention?

Breast cancer is the most commonly diagnosed cancer in women. The risk of developing breast cancer can be lowered by maintaining a healthy bodyweight and avoiding long-term use of combined estrogen and progestogen replacement after menopause. However, many women are at an increased risk of developing breast cancer secondary to age, early menarche, a family history of breast cancer or a personal history of benign breast disease. These women may now be offered tamoxifen as a chemoprevention therapy. Five years of tamoxifen treatment results in a reduction in the relative risk of developing estrogen receptor-positive breast cancer of 48%. This benefit outweighs the risk of tamoxifen-related adverse events for many healthy women. However, the benefit-risk ratio of tamoxifen chemoprevention varies for individual women. The randomized clinical trials evaluating standard-dose tamoxifen versus placebo as chemoprevention therapy are reviewed and analyzed to determine which particular women are most likely to benefit and least likely to experience a tamoxifen-related adverse event. Tamoxifen decreases the risk of breast cancer associated with aging, having a first-degree relative with disease, and a personal diagnosis of atypical ductal hyperplasia or lobular carcinoma in situ. Women who have had a hysterectomy and are at low risk of a thromboembolic event have a decreased risk of adverse effects associated with tamoxifen therapy. The strengths and weaknesses of the Gail model (frequently used to assess an individual's risk of developing invasive breast cancer over the next 5 years) are highlighted. A method for assessing the benefit-risk ratio for an individual woman is presented. Alternative breast cancer chemoprevention strategies are considered, including the use of aromatase inhibitors. This article discusses the pros and cons of these various preventive therapies and concludes that at this time, tamoxifen remains the gold standard for breast cancer prevention.

Recurrent endometrial polyps in postmenopausal breast cancer patients on tamoxifen

Objectives Endometrial polyps are the most common endometrial pathology described in association with postmenopausal tamoxifen exposure, with an incidence of up to 10.7% of malignancy. Some women tend to develop recurrent polyps. However, no one has yet described any risk factors for the development of recurrent endometrial polyps in postmenopausal breast cancer tamoxifen-treated patients. Methods We compared various clinical features of 64 postmenopausal breast cancer tamoxifen-treated patients with a primary endometrial polyp (Group I), with those of 27 similar patients with recurrent polyps (Group 2). Results Previous exposure to hormone replacement therapy was significantly more common and duration of tamoxifen treatment, up to the diagnosis of primary endometrial polyp, was significantly shorter in Group II patients ( P = 0.0217 and P = 0.0148, respectively). Logistic regression analysis revealed that the combination of shorter tamoxifen exposure before the diagnosis of primary polyp, lower parity, lower menopausal age at the diagnosis of primary polyp, and higher years of tamoxifen treatment was found to increase significantly the risk of developing recurrent endometrial polyps. Any additional year of tamoxifen treatment may increase by fivefold the risk of developing recurrent polyps. There was no significant difference in ultrasonographic endometrial thickness measured before resection of the primary polyps in both groups and before the resection of recurrent polyps in Group II. Conclusions Previous use of HRT, shorter duration of tamoxifen exposure, and additional years of tamoxifen treatment may significantly increase the risk of developing recurrent endometrial polyps in postmenopausal breast cancer tamoxifen-treated patients.

The influence of tamoxifen treatment on the oestrogen receptor in metachronous contralateral breast cancer

Adjuvant tamoxifen treatment reduces the occurrence of contralateral breast cancer (CBC). The aim of the study was to investigate the hypothesis that adjuvant tamoxifen reduces the occurrence of oestrogen-receptor (ER)-positive CBC, but not the growth of ER-negative CBCs, and to examine survival after diagnosis of CBC. For the study, ER status was immunohistochemically assessed in CBCs of 35 tamoxifen-treated patients and 115 patients without previous hormonal treatment. Cases were retrieved from a series of patients treated from 1984 to 1995 at nine hospitals. The interval between ipsi- and contralateral breast cancer was at least 1 year. It was seen that the proportion of patients with an ER-negative CBC was significantly higher among those with prior tamoxifen treatment: 37% vs 18% (P=0.047). No difference between the two groups in overall and disease-specific survival following CBC was found. However, the stage differed for both groups: tamoxifen users more often had node-positive contralateral disease (P= 0.045). In conclusion, metachronous CBCs developing after 1–3 years of tamoxifen treatment are more often ER-negative breast cancers. So far this does not seem to have a major impact on survival.

Asymptomatic Acute Pancreatitis Due to Tamoxifen-Induced Severe Hypertriglyceridemia in a Patient with Diabetes Mellitus and Breast Cancer

We report tamoxifen-induced hypertriglyceridemia and asymptomatic acute pancreatitis in a 51 year-old women with type 2 diabetes mellitus and stage III-b infiltrative ductal carcinoma, admitted to the hospital with weakness, oliguria and glucose dysregulation. On admission, there was no fever, abdominal or back pain, rebound tenderness, nausea, or vomiting. Following 1 year of tamoxifen treatment, triglycerides increased from 400 to 1344 mg/dl (blood urea nitrogen 52 mg/dl, creatinine 2.0 mg/dl, glucose 341 mg/dl). Hypertriglyceridemia was considered to be due to either diabetic dyslipidemia and/or tamoxifen. On computerized tomography, pancreatic enlargement, het-erogenity, hypodensity and a pancreatic pseudocyst (5 × 7.5 cm diameter) were found. Acute pancreatitis was suspected, and serum amylase level was found to be increased (273 IU/L). Tamoxifen was discontinued and gemfibrozil was started. Triglycerides decreased to 301 mg/dl and amylase decreased to 66 IU/L a week later and remained normal thereafter. This case indicates that tamoxifen-induced hypertriglyceridemia may cause acute pancreatitis without classical symptoms which might be due to autonomic neuropathy in diabetic patients. Effects on lipid metabolism should be considered and triglycerides should be closely followed in patients on tamoxifen.

Uterine side effects of treatment with tamoxifen

Objective: To assess a causal the relationship between endometrial lesions and tamoxifen therapy in patients with breast cancer. Design: Prospective longitudinal study and cross-sectional study. Setting: Cancer prevention unit at Basurto Hospital, Bilbao. Population and methods: Three populations of breast cancer were studied: 43 before the beginning of tamoxifen; 78 after 5–72 months of tamoxifen, and 34 before tamoxifen and after 12–24 months of tamoxifen treatment (PAIRED GROUP). All of them were systematically studied with CO 2 diagnostic hysteroscopy and endometrial biopsy by the same clinician. Results: Before tamoxifen, the following endometrial lesions were detected: endometrial polyps 9.3%; endometrial cysts 16.3%; synechiae 11.6%. In the paired group the ingestion of tamoxifen shows a direct causal effect with a significant increase in endometrial polyps (11.8% vs. 29.4%; OR=13; CI=7.9–18.1), in endometrial cysts (17.7% vs. 55.9%; OR=7.5; CI=5.9–9.1) and in synechiae (14.7% vs. 35.5%; OR=8; CI=4.7–11.3). In the group under tamoxifen for 5–72 months, one endometrial carcinoma was detected. Conclusions: Breast cancer patients have a number of endometrial lesions before undergoing any hormonal therapy. Tamoxifen significantly increased benign endometrial lesions, usually after less than one year of treatment. No cases of endometrial carcinoma was found in our series of 34 patients with 1–2 years of tamoxifen treatment, and 1/78 in patients with 5–72 months of tamoxifen.

Chemotherapy versus tamoxifen versus chemotherapy plus tamoxifen in node-positive, estrogen receptor-positive breast cancer patients: results of a multicentric Italian study. Breast Cancer Adjuvant Chemo-Hormone Therapy Cooperative Group.

Between November 1, 1983 and June 30, 1987, 510 node-positive, estrogen receptor (ER)-positive breast cancer patients have been randomly allocated to receive either chemotherapy (six intravenous [IV] cyclophosphamide, methotrexate, and fluorouracil [CMF] courses followed by four IV epirubicin courses) or 5 years of tamoxifen treatment or a combination of both therapies. After a median follow-up of 40 months, patients receiving the combined treatment achieved the best results, and those treated with chemotherapy alone achieved the worst, the difference being particularly evident in postmenopausal women. However, while the concurrent use of chemotherapy and tamoxifen did improve the results achieved by chemotherapy alone, particularly in postmenopausal women and in those with four or more involved nodes, it did not significantly improve the results achieved by tamoxifen alone, particularly in patients with higher ER tumor concentrations. Side effects were more numerous and more severe in patients receiving chemotherapy (with or without tamoxifen). Our findings, although still preliminary, confirm that tamoxifen should be the treatment of choice for postmenopausal breast cancer patients with node-positive, ER-positive tumors. In addition, the findings suggest that tamoxifen may represent a safe alternative to chemotherapy (at least to the cytotoxic regimen we used) for younger women, provided they have ER-positive tumors. In patients with ER-positive tumors, the addition of chemotherapy to tamoxifen does not seem to improve significantly the effectiveness of tamoxifen alone.

Assessment of medication unblinding in the multicenter diltiazem post-infarction trial: Mary W. Brown, Arthur J. Moss and Eric Carleen University of Rochester, Rochester. New York(P33)

Background: In postmenopausal women with hormone-sensitive early stage breast cancer, the risk for relapse persists after 5 years of treatment with adjuvant tamoxifen. Because tamoxifen is not indicated for adjuvant therapy beyond 5 years, the need for another therapy in the extended adjuvant setting to reduce late recurrence risk is clear. The National Cancer Institute of Canada Clinical Trials Group MA.17 and the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-33 trial found that extended adjuvant therapy with an aromatase inhibitor (AI) (eg, letrozole, exemestane, or anastrozole) rendered additional benefit in postmenopausal women with hormone receptor-positive breast cancer. The MA.17 trial was unblinded at the first interim analysis (median follow-up, 2.4 years) due to a significant reduction in relative risk for recurrence (P < 0.001). Following the publication of the final analysis, several other MA.17 trial analyses and a postblinding analysis were also conducted. Recent data on the NSABP B-33 trial, which investigated exemestane in the extended adjuvant setting, and Austrian Breast and Colorectal Cancer Study Group (ABCSG) trial 6a, which evaluated anastrozole in the extended adjuvant setting, have also been reported.Objective: The goal of this article was to provide a current review of the MA.17 and NSABP B-33 resuits, together with additional data, to determine the benefit and tolerability of extended adjuvant AI therapy and the potential benefits of late extended adjuvant therapy with AIs after a prolonged (≤5 years) period after the completion of tamoxifen treatment.Methods: A literature search was performed. PubMed and MEDLINE were searched for descriptions of clinical trials published from 1990 to 2007 using the terms breast cancer, extended adjuvant, aromatase inhibitor, anastrozole, exemestane, and letrozole. Abstracts from several oncology meetings held between 2001 and 2007 also were searched to extract relevant data (disease-free survival [DFS], overall survival [OS]).Results: In MA.17 at 30 months, postmenopausal patients with early stage breast cancer who received extended adjuvant letrozole (n = 2593) experienced a significant (42%) improvement in DFS regardless of nodal status (P < 0.001), and there was a significant (39%) improvement in as in node-positive patients (P = 0.04), compared with placebo. At median follow-up (54 months), a postunblinding analysis found that patients who were switched to letrozole after a prolonged period (up to 5 years) after discontinuation of tamoxifen experienced a 69% improvement in DFS (P < 0.001), a 72% improvement in distant DFS (P = 0.002), and a 47% improvement in as (P = 0.05) compared with patients who elected to continue with no treatment at trial unblinding. Results from 2 other extended adjuvant trials, the NSABP B-33, investigating exemestane in the extended setting (relapse-free survival, P = 0.03; no significant improvement in DFS or as), and the smaller ABCSG 6a, also support a benefit of extended adjuvant AI therapy.Conclusions: Current evidence supports the use of letrozole and perhaps exemestane in the extended adjuvant setting, while data on anastrozole are emerging. Based on the results from this review, initiation of letrozole treatment following a prolonged interval after completion of 5 years of tamoxifen treatment might be beneficial.