Clodronate.

Two early observations about the first generation bisphosphonate, clodronate, suggested that it would likely have clinical utility; specifically, it was a more potent anti-resorptive but a less potent inhibitor of mineralisation than its predecessor etidronate. The known mechanism of action differs from that of the later nitrogen-containing bisphosphonates, as clodronate is metabolised intracellularly to a toxic analog of adenosine triphosphate, AppCCl2p, which causes mitochondrial dysfunction, impaired cellular energy metabolism and osteoclast apoptosis. For pre-clinical studies in a variety of disease models, liposomal clodronate has become the agent of choice for macrophage depletion, for example in a recent study to enhance haematopoietic chimerism and donor-specific skin allograft tolerance in a mouse model. For clinical use, clodronate was developed in oral and injectable formulations; while poorly absorbed from the gastro-intestinal tract, its absorption at 1-3% of the administered dose is approximately three-fold higher than for nitrogen-containing bisphosphonates. Following an early setback due to an erroneous association with toxic adverse events, a number of successful clinical studies have established clodronate, predominantly in its oral formulations, as a highly successful treatment in Paget's disease, hypercalcaemia (benign and malignant), multiple myeloma, and early or metastatic breast cancer. Novel uses in other disease areas, including veterinary use, continue to be explored.

Immunohistochemical Phenotype of Breast Cancer during 25-Year Follow-up of the Royal Marsden Tamoxifen Prevention Trial.

The randomized, double-blinded Royal Marsden Tamoxifen Breast Cancer Prevention Trial in healthy high-risk women started in 1986 and is still blinded. Eligible participants (n = 2,471) were randomly assigned to tamoxifen (20 mg/d) or placebo for 8 years. Analysis in 2006 showed a 30% risk reduction of estrogen receptor (ER)-positive invasive breast cancer mostly in the posttreatment period. Biomarker analysis in this population may identify any subgroup-specific preventive effects tamoxifen. After a median follow-up of 18.4 years, 242 patients had developed invasive cancer, 134 on placebo and 108 on tamoxifen. From these, 180 tissue blocks were available and ER, progesterone receptor (PgR), Ki67, HER2, and EGFR were immunohistochemically analyzed. A 32% reduction in ER+ and PgR+ invasive cancers resulted after 8 years of treatment. Quantitative levels of ER and PgR were lower in the tamoxifen-treated group, significantly so for ER (P = 0.001). These lower ER levels were restricted to the posttreatment period (P = 0.018). Among the ER+ group, there was a similar proportional decrease in PgR+ and PgR- tumors by tamoxifen. The median levels of Ki67 were similar in both arms. The numbers of HER2-positive and EGFR-positive cancers were higher in the tamoxifen arm but not significantly so. In conclusion, the preventive effects of tamoxifen result in reduced ER-positive but not ER-negative tumors and reduced ER expression in the ER-positive cases largely confined to the posttreatment period. Overall reductions in PgR expression are explained by lower frequency of ER-positive cases. Impact on Ki67, HER2, and EGFR was modest. Cancer Prev Res; 10(3); 171-6. ©2017 AACR.

Impact of a Panel of 88 Single Nucleotide Polymorphisms on the Risk of Breast Cancer in High-Risk Women: Results From Two Randomized Tamoxifen Prevention Trials.

Purpose At least 94 common single nucleotide polymorphisms (SNPs) are associated with breast cancer. The extent to which an SNP panel can refine risk in women who receive preventive therapy has not been directly assessed previously. Materials and Methods A risk score on the basis of 88 SNPs (SNP88) was investigated in a nested case-control study of women enrolled in the International Breast Intervention Study (IBIS-I) or the Royal Marsden study. A total of 359 women who developed cancer were matched to 636 controls by age, trial, follow-up time, and treatment arm. Genotyping was done using the OncoArray. Conditional logistic regression and matched concordance indices (mC) were used to measure the performance of SNP88 alone and with other breast cancer risk factors assessed using the Tyrer-Cuzick (TC) model. Results SNP88 was predictive of breast cancer risk overall (interquartile range odds ratio [IQ-OR], 1.37; 95% CI, 1.14 to 1.66; mC, 0.55), but mainly for estrogen receptor-positive disease (IQ-OR, 1.44; 95% CI, 1.16 to 1.79; P for heterogeneity = .10) versus estrogen receptor-negative disease. However, the observed risk of SNP88 was only 46% (95% CI, 19% to 74%) of expected. No significant interaction was observed with treatment arm (placebo IQ-OR, 1.46; 95% CI, 1.13 to 1.87; tamoxifen IQ-OR, 1.25; 95% CI, 0.96 to 1.64; P for heterogeneity = .5). The predictive power was similar to the TC model (IQ-OR, 1.45; 95% CI, 1.21 to 1.73; mC, 0.55), but SNP88 was independent of TC (Spearman rank-order correlation, 0.012; P = .7), and when combined multiplicatively, a substantial improvement was seen (IQ-OR, 1.64; 95% CI, 1.36 to 1.97; mC, 0.60). Conclusion A polygenic risk score may be used to refine risk from the TC or similar models in women who are at an elevated risk of breast cancer and considering preventive therapy. Recalibration may be necessary for accurate risk assessment.

Relationship of ZNF423 and CTSO with breast cancer risk in two randomised tamoxifen prevention trials.

A case-control study from two randomised breast cancer prevention trials of tamoxifen and raloxifene (P-1 and P-2) identified single-nucleotide polymorphisms (SNPs) in or near genes ZNF423 and CTSO as factors which predict which women will derive most anti-cancer benefit from selective oestrogen receptor modulator (SERM) therapy. In this article, we further examine this question using blood samples from two randomised tamoxifen prevention trials: the International Breast Cancer Intervention Study I (IBIS-I) and the Royal Marsden trial (Marsden). A nested case-control study was designed with 2:1 matching in IBIS-I and 1:1 matching in Marsden. The OncoArray was used for genotyping and included two SNPs previously identified (rs8060157 in ZNF423 and rs10030044 near CTSO), and 102 further SNPs within the same regions. Overall, there were 369 cases and 662 controls, with 148 cases and 268 controls from the tamoxifen arms. Odds ratios were estimated by conditional logistic regression, with Wald 95 % confidence intervals. In the tamoxifen arms, the per-allele odds ratio for rs8060157 was 0.99 (95 %CI 0.73-1.34) and 1.00 (95 %CI 0.76-1.33) for rs10030044. In the placebo arm, the odds ratio was 1.10 (95 %CI 0.87-1.40) for rs8060157 and 1.01 (95 %CI 0.79-1.29) for rs10030044. There was no evidence to suggest that other SNPs in the surrounding regions of these SNPs might predict response to tamoxifen. Results from these two prevention trials do not support the earlier findings. rs8060157 in ZNF423 and rs10030044 near CTSO do not appear to predict response to tamoxifen.

Selective oestrogen receptor modulators in prevention of breast cancer: an updated meta-analysis of individual participant data.

BACKGROUND: Tamoxifen and raloxifene reduce the risk of breast cancer in women at elevated risk of disease, but the duration of the effect is unknown. We assessed the effectiveness of selective oestrogen receptor modulators (SERMs) on breast cancer incidence. METHODS: We did a meta-analysis with individual participant data from nine prevention trials comparing four selective oestrogen receptor modulators (SERMs; tamoxifen, raloxifene, arzoxifene, and lasofoxifene) with placebo, or in one study with tamoxifen. Our primary endpoint was incidence of all breast cancer (including ductal carcinoma in situ) during a 10 year follow-up period. Analysis was by intention to treat. RESULTS: We analysed data for 83,399 women with 306,617 women-years of follow-up. Median follow-up was 65 months (IQR 54-93). Overall, we noted a 38% reduction (hazard ratio [HR] 0·62, 95% CI 0·56-0·69) in breast cancer incidence, and 42 women would need to be treated to prevent one breast cancer event in the first 10 years of follow-up. The reduction was larger in the first 5 years of follow-up than in years 5-10 (42%, HR 0·58, 0·51-0·66; p<0·0001 vs 25%, 0·75, 0·61-0·93; p=0·007), but we noted no heterogeneity between time periods. Thromboembolic events were significantly increased with all SERMs (odds ratio 1·73, 95% CI 1·47-2·05; p<0·0001). We recorded a significant reduction of 34% in vertebral fractures (0·66, 0·59-0·73), but only a small effect for non-vertebral fractures (0·93, 0·87-0·99). INTERPRETATION: For all SERMs, incidence of invasive oestrogen (ER)-positive breast cancer was reduced both during treatment and for at least 5 years after completion. Similar to other preventive interventions, careful consideration of risks and benefits is needed to identify women who are most likely to benefit from these drugs. FUNDING: Cancer Research UK.

Breast cancer incidence in postmenopausal women with osteoporosis or low bone mass using arzoxifene.

The Generations trial, a multicenter, placebo-controlled, double-blind trial, compared arzoxifene 20 mg/day and placebo in 9,354 postmenopausal women with osteoporosis (N=5,252) or low bone mass (N=4,102). Primary outcomes were vertebral fracture in the osteoporotic population and invasive breast cancer in all study participants. Here, we report the detailed breast cancer findings from the trial. Breast cancers were detected by annual mammograms and clinical examination. After 48 months follow-up, breast cancer incidence was compared between treatment groups by estrogen receptor (ER) and progesterone receptor (PR) status and baseline risk factors. Baseline breast cancer risk factors, including age, estimated Gail risk, and bone mineral density, were well balanced between treatment groups. A total of 75 breast cancers occurred 53 in the placebo group and 22 in the arzoxifene group (HR 0.41, 95% CI 0.25-0.68, P<0.001). There were 62 invasive breast cancers, 39 identified as invasive ER-positive (placebo 30, arzoxifene 9; HR 0.30, 95% CI 0.14-0.63, P=0.001) and 30 identified as invasive PR-positive (placebo 23, arzoxifene 7; HR 0.30, 95% CI 0.13-0.71, P=0.003). Breast cancer risk reduction with arzoxifene was similar between Gail risk groups (P interaction=0.31) and between low bone mass and osteoporosis groups (P interaction=0.35). Although generally well tolerated, there was a significant increase in venous thromboembolism, vasomotor symptoms, muscle cramps, and some gynecological events with arzoxifene. These findings demonstrate that in this study arzoxifene reduced the risk of ER-positive breast cancer in this population of postmenopausal women with low bone mass or osteoporosis, an effect similar to that seen with other SERMs.

Prevention of breast cancer by newer SERMs in the future.

The selective oestrogen receptor modulators (SERMs) tamoxifen has been shown to reduce the incidence of oestrogen receptor positive breast cancer by about 60 to 70% in healthy high risk women. The oestrogenic effects of tamoxifen caused a beneficial effect of reduced bone loss and fracture risk in postmenopausal women. However there was also significant gynaecological toxicity including an increased risk of endometrial cancer. Further clinical trials have evaluated the newer SERMs raloxifene, arzoxifene and lasofoxifene. The latter has been shown to significantly reduce the incidence of breast cancer, vertebral and non vertebral fractures, major coronary events and stroke with no significant gynaecological toxicity.

Arzoxifene for prevention of fractures and invasive breast cancer in postmenopausal women.

Arzoxifene is a selective estrogen receptor modulator (SERM) that has been shown to be more potent in preclinical testing than currently available agents. Its effects on clinical outcomes are not known. In a randomized, blinded trial, women aged 60 to 85 years with osteoporosis, defined as a femoral neck or lumbar spine bone mineral density T-score of -2.5 or less or a vertebral fracture, and women with low bone mass, defined as a bone density T-score of -1.0 or less and above -2.5, were assigned to arzoxifene 20 mg or placebo daily. The primary endpoints were new vertebral fracture in those with osteoporosis and invasive breast cancer in the overall population. After 3 years, the cumulative incidence of vertebral fractures in patients with osteoporosis was 2.3% lower in the arzoxifene group than in the placebo group, a 41% relative risk reduction [95% confidence interval (CI) 0.45-0.77, p < .001]. In the overall population, the cumulative incidence of invasive breast cancer over 4 years was reduced by 1.3%, with a 56% relative reduction in risk (hazard ratio = 0.44, 95% CI 0.26-0.76, p < .001); there was no significant decrease in nonvertebral fracture risk. Arzoxifene increased the cumulative incidence of venous thromboembolic events by 0.7%, with a 2.3-fold relative increase (95% CI 1.5-3.7). Like other SERMs, arzoxifene decreased vertebral fractures and invasive breast cancer while the risk of venous thromboembolic events increased.

Breast cancer incidence in the randomized PEARL trial of lasofoxifene in postmenopausal osteoporotic women.

BACKGROUND: Currently available selective estrogen receptor modulators reduce the risk of breast cancer, but they are not widely used. In the Postmenopausal Evaluation and Risk-Reduction with Lasofoxifene (PEARL) trial, lasofoxifene was shown to reduce the risk of estrogen receptor-positive (ER+) breast cancer, nonvertebral and vertebral fractures, coronary artery disease, and stroke, but the effects on total breast cancer (invasive and ductal carcinoma in situ, ER+ and estrogen receptor-negative [ER-]) and ER+ invasive breast cancer are unknown. METHODS: Postmenopausal women (n = 8556) aged 59-80 years with low bone density and normal mammograms were randomly assigned to two doses of lasofoxifene (0.25 and 0.5 mg) or placebo. The primary endpoints of the PEARL trial were incidence of ER+ breast cancer and nonvertebral fractures at 5 years. A nested case-control study of 49 incident breast cancer case patients and 156 unaffected control subjects from the PEARL trial was performed to evaluate treatment effects on risk of total and ER+ invasive breast cancer by baseline serum estradiol and sex hormone-binding globulin levels using logistic regression models. Cox proportional hazards models were used to evaluate risk of total breast cancer and ER+ invasive breast cancer using intention-to-treat analysis. All statistical tests were two-sided. RESULTS: Breast cancer was confirmed in 49 women. Compared with placebo, 0.5 mg of lasofoxifene statistically significantly reduced the risk of total breast cancer by 79% (hazard ratio = 0.21; 95% confidence interval [CI] = 0.08 to 0.55) and ER+ invasive breast cancer by 83% (hazard ratio = 0.17; 95% CI = 0.05 to 0.57). The effects of 0.5 mg of lasofoxifene on total breast cancer were similar regardless of Gail score, whereas the effects were markedly stronger for women with baseline estradiol levels greater than the median (odds ratio = 0.11; 95% CI = 0.02 to 0.51) vs those with levels less than the median (odds ratio = 0.78; 95% CI = 0.16 to 3.79; P(interaction) = .04). CONCLUSION: A 0.5-mg dose of lasofoxifene appears to reduce the risks of both total and ER+ invasive breast cancer in postmenopausal women with osteoporosis.

Lasofoxifene in postmenopausal women with osteoporosis.

BACKGROUND: The effects of lasofoxifene on the risk of fractures, breast cancer, and cardiovascular disease are uncertain. METHODS: In this randomized trial, we assigned 8556 women who were between the ages of 59 and 80 years and had a bone mineral density T score of -2.5 or less at the femoral neck or spine to receive once-daily lasofoxifene (at a dose of either 0.25 mg or 0.5 mg) or placebo for 5 years. Primary end points were vertebral fractures, estrogen receptor (ER)-positive breast cancer, and nonvertebral fractures; secondary end points included major coronary heart disease events and stroke. RESULTS: Lasofoxifene at a dose of 0.5 mg per day, as compared with placebo, was associated with reduced risks of vertebral fracture (13.1 cases vs. 22.4 cases per 1000 person-years; hazard ratio, 0.58; 95% confidence interval [CI], 0.47 to 0.70), nonvertebral fracture (18.7 vs. 24.5 cases per 1000 person-years; hazard ratio, 0.76; 95% CI, 0.64 to 0.91), ER-positive breast cancer (0.3 vs. 1.7 cases per 1000 person-years; hazard ratio, 0.19; 95% CI, 0.07 to 0.56), coronary heart disease events (5.1 vs. 7.5 cases per 1000 person-years; hazard ratio, 0.68; 95% CI, 0.50 to 0.93), and stroke (2.5 vs. 3.9 cases per 1000 person-years; hazard ratio, 0.64; 95% CI, 0.41 to 0.99). Lasofoxifene at a dose of 0.25 mg per day, as compared with placebo, was associated with reduced risks of vertebral fracture (16.0 vs. 22.4 cases per 1000 person-years; hazard ratio, 0.69; 95% CI, 0.57 to 0.83) and stroke (2.4 vs. 3.9 cases per 1000 person-years; hazard ratio, 0.61; 95% CI, 0.39 to 0.96) Both the lower and higher doses, as compared with placebo, were associated with an increase in venous thromboembolic events (3.8 and 2.9 cases vs. 1.4 cases per 1000 person-years; hazard ratios, 2.67 [95% CI, 1.55 to 4.58] and 2.06 [95% CI, 1.17 to 3.60], respectively). Endometrial cancer occurred in three women in the placebo group, two women in the lower-dose lasofoxifene group, and two women in the higher-dose lasofoxifene group. Rates of death per 1000 person-years were 5.1 in the placebo group, 7.0 in the lower-dose lasofoxifene group, and 5.7 in the higher-dose lasofoxifene group. CONCLUSIONS: In postmenopausal women with osteoporosis, lasofoxifene at a dose of 0.5 mg per day was associated with reduced risks of nonvertebral and vertebral fractures, ER-positive breast cancer, coronary heart disease, and stroke but an increased risk of venous thromboembolic events. (ClinicalTrials.gov number, NCT00141323.)

Effect of oral clodronate on bone mass, bone turnover and subsequent metastases in women with primary breast cancer.

Breast cancer treatments have been associated with accelerated bone loss and increased osteoporosis risk. In a subgroup analysis of a randomised, double-blind, placebo-controlled study, we compared the changes in spine and total hip bone mineral density (BMD) and biochemical markers of bone turnover in women with primary breast cancer who had received standard therapy plus either oral clodronate 1600 mg/d (n=419) or placebo (n=432) for 2 years. After 2 years, spine BMD was 1.92% higher in patients who received clodronate instead of placebo (P<0.0001) and total hip BMD was 1.29% higher (P=0.002 versus placebo). Patients who received clodronate had a median 26% reduction in levels of serum N-terminal pro-peptide of type I procollagen (PINP)--a marker of bone turnover--after 2 years of therapy. This compares with a median 5% increase in patients who received placebo (P<0.0001). Effects on BMD, but not biochemical markers, persisted for up to 3 years post-treatment. Early changes in PINP were associated with changes in BMD and the likelihood of developing bone metastases. This study shows the use of oral clodronate during primary breast cancer treatment is associated with reduced bone turnover and protection against bone metastases.

Prevention of breast cancer using SERMs.

The development of breast cancer is dependant in part on oestrogen. Suppression of ovarian function or use of anti-oestrogens will reduce the incidence of breast cancer. Many trials have now been done involving tens of thousands of healthy women evaluating the use of selective oestrogen receptor modulators to reduce the risk of breast cancer in healthy women. Tamoxifen will reduce the early incidence of breast cancer in pre and postmenopausal women by about 40% but causes vasomotor symptoms, thromboembolism and gynaecological toxicity including polyps, endometrial atypia and rarely cancer. In long follow up trials the risk reduction for breast cancer extends beyond the treatment period out to at least 15 years appearing to get larger with time indicating a true long term prevention effect. The toxicity of tamoxifen is for the most part confined to the treatment period. Raloxifene also has similar breast cancer risk reduction activity to tamoxifen but has less toxicity with no evidence of an increased risk of endometrial atypia or cancer. Tamoxifen is licensed for breast cancer risk reduction in the USA and raloxifene has also recently been approved by the FDA for such use.

Guidance for the management of breast cancer treatment-induced bone loss: a consensus position statement from a UK Expert Group.

In postmenopausal women, the use of aromatase inhibitors increases bone turnover and induces bone loss at sites rich in trabecular bone at an average rate of 1-3% per year leading to an increase in fracture incidence compared to that seen during tamoxifen use. The bone loss is much more marked in young women with treatment-induced ovarian suppression followed by aromatase inhibitor therapy (average 7-8% per annum). Pre-treatment with tamoxifen for 2-5 years may reduce the clinical significance of the adverse bone effects associated with aromatase inhibitors, particularly if this leads to a shortening in the duration of exposure to an aromatase inhibitor. However, skeletal status should still be assessed at the commencement of aromatase inhibitor therapy. The rate of bone loss in women who experience a premature menopause before the age of 45 or are receiving ovarian suppression therapy is accelerated by the concomitant use of aromatase inhibitors. These patients are considered to be at high risk of clinically important bone loss and should have a baseline dual energy X-ray absorptiometry (DXA) assessment of bone mineral density (BMD). Randomised clinical trials in postmenopausal women indicate that bisphosphonates prevent the bone loss and accelerated bone turnover associated with aromatase inhibitor therapy and are a promising strategy for the prevention and treatment of osteoporosis in this setting. Treatment initiation recommendations are based on a combination of risk factors for osteoporotic fracture and BMD levels. Bisphosphonates, along with a healthy lifestyle and adequate intake of calcium and vitamin D are the treatments of choice to prevent bone loss. Due to the rate of bone loss associated with breast cancer treatments, and uncertainties about the interaction between aromatase inhibitor use and BMD for fracture risk, the threshold for intervention has been set at a higher level than that generally recommended for postmenopausal osteoporosis. Management recommendations have been summarised in two algorithms, one for women experiencing a premature menopause and the other for postmenopausal women requiring adjuvant aromatase inhibitor therapy.

Red clover isoflavones are safe and well tolerated in women with a family history of breast cancer.

OBJECTIVE: To assess the safety and tolerability of a standardized 40 mg red clover isoflavone dietary supplement (Promensil, Novogen) in women with a family history of breast cancer to evaluate the feasibility of using the supplement for prevention of breast cancer in healthy women. STUDY DESIGN: Healthy women aged 35-70 years (n = 401) with at least one first-degree relative with breast cancer received red clover isoflavones or placebo for three years in a randomized, double-blind, placebo-controlled pilot trial. Participants were assessed clinically and blood samples taken for biochemical analysis every six months. In addition, study participants underwent mammography, bone density and transvaginal ultrasound (postmenopausal women only) once per year. RESULTS: No significant differences in breast density, endometrial thickness, serum cholesterol, follicle stimulating hormone levels and bone mineral density were detected between those taking red clover isoflavones and placebo. In postmenopausal women, some significant differences in bone marker levels were seen between active and placebo groups, at six months and at 12 months. The adverse event profile was similar across all red clover isoflavone and placebo groups. CONCLUSION: This three-year study supports the growing body of evidence that treatment with red clover isoflavones is safe and well tolerated in healthy women. Supplements containing red clover isoflavones did not adversely affect breast density, skeletal strength or cardiovascular status. In postmenopausal women, endometrial status was not adversely affected. The adverse event profile was similar between red clover isoflavones, and placebo and endocrine status did not differ.

Twenty-year follow-up of the Royal Marsden randomized, double-blinded tamoxifen breast cancer prevention trial.

BACKGROUND: Several clinical trials have reported an early reduction in breast cancer incidence in healthy women using tamoxifen to reduce their risk of breast cancer but have not reported longer follow-up data for the evaluation of breast cancer prevention. We report the blinded 20-year follow-up (median follow-up = 13 years) of the Royal Marsden trial to identify any long-term prevention of breast cancer associated with tamoxifen treatment. METHODS: We randomly assigned 2494 healthy women to oral tamoxifen (20 mg/day) or placebo for 8 years. The primary outcome was occurrence of invasive breast cancer. A secondary planned analysis of estrogen receptor (ER)-positive invasive breast cancer was also done. Survival was assessed by use of a Cox proportional hazards model in both univariate and multivariable analyses. The durability of the treatment effect was assessed by use of a Cox regression analysis. All statistical tests were two-sided. RESULTS: Among the 2471 eligible participants (1238 participants in the tamoxifen arm and 1233 participants in the placebo arm), 186 developed invasive breast cancer (82 on tamoxifen and 104 on placebo; hazard ratio [HR] = 0.78, 95% confidence interval [CI] = 0.58 to 1.04; P = .1). Of these 186 cancers, 139 were ER positive (53 on tamoxifen and 86 on placebo; HR = 0.61, 95% CI = 0.43 to 0.86; P = .005). The risk of ER-positive breast cancer was not statistically significantly lower in the tamoxifen arm than in the placebo arm during the 8-year treatment period (30 cancers in the tamoxifen arm and 39 in the placebo arm; HR = 0.77, 95% CI = 0.48 to 1.23; P = .3) but was statistically significantly lower in the posttreatment period (23 in the tamoxifen arm and 47 in the placebo arm; HR = 0.48, 95% CI = 0.29 to 0.79; P = .004). Fifty-four participants in each arm have died from any cause (HR = 0.99, 95% CI = 0.68 to 1.44; P = .95). The adverse event profiles for both arms were similar to those previously reported and occurred predominantly during the treatment period. CONCLUSIONS: A statistically significant reduction in the incidence of ER-positive breast cancer was observed in the tamoxifen arm that occurred predominantly during the post treatment follow-up, indicating long-term prevention of estrogen-dependent breast cancer by tamoxifen.