Metformin, an insulin-lowering agent, has been associated with decreased cancer risk in epidemiologic studies in diabetic patients. We performed a comprehensive literature search and meta-analysis of epidemiologic studies to assess the effect of metformin on cancer incidence and mortality in diabetic patients, using Pubmed, ISI Web of Science, Embase, and the Cochrane library until May 2009, with no language or time restrictions. Independent reports with sufficient information to allow risk estimation of cancer risk/mortality and a measure of uncertainty were reviewed and cross-checked independently by three investigators. Eleven studies were selected for relevance in terms of intervention, population studied, independence, and reporting of cancer incidence or mortality data, reporting 4,042 cancer events and 529 cancer deaths. A 31% reduction in overall summary relative risk (0.69; 95% confidence interval, 0.61-0.79) was found in subjects taking metformin compared with other antidiabetic drugs. The inverse association was significant for pancreatic and hepatocellular cancer, and nonsignificant for colon, breast, and prostate cancer. A trend to a dose-response relationship was noted. Metformin is associated with a decreased risk of cancer incidence compared with other treatments among diabetic patients. Given the retrospective nature of most studies and the possibility that the control treatments increase risk, phase II trials are needed before large cancer prevention trials are launched. Cancer Prev Res; 3(11); 1451–61. ©2010 AACR.

PURPOSE: Tamoxifen administered for 5 years at 20 mg/d is effective in breast cancer treatment and prevention, but toxicity has limited its broad use. Biomarker trials showed that 5 mg/d is not inferior to 20 mg/d in decreasing breast cancer proliferation. We hypothesized that a lower dose given for a shorter period could be as effective in preventing recurrence from breast intraepithelial neoplasia but have a lower toxicity than the standard dose. PATIENTS AND METHODS: We conducted a multicenter randomized trial of tamoxifen, 5 mg/d or placebo administered for 3 years after surgery in women with hormone-sensitive or unknown breast intraepithelial neoplasia, including atypical ductal hyperplasia and lobular or ductal carcinoma in situ. The primary end point was the incidence of invasive breast cancer or ductal carcinoma in situ. RESULTS: Five hundred women 75 years of age or younger were included. After a median follow-up of 5.1 years (interquartile range, 3.9-6.3 years), there were 14 neoplastic events with tamoxifen and 28 with placebo (11.6 v 23.9 per 1,000 person-years; hazard ratio, 0.48; 95% CI, 0.26 to 0.92; P = .02), which resulted in a 5-year number needed to treat of 22 (95% CI, 20 to 27). Tamoxifen decreased contralateral breast events by 75% (three v 12 events; hazard ratio, 0.25; 95% CI, 0.07 to 0.88; P = .02). Patient-reported outcomes were not different between arms except for a slight increase in frequency of daily hot flashes with tamoxifen ( P = .02). There were 12 serious adverse events with tamoxifen and 16 with placebo, including one deep vein thrombosis and one stage I endometrial cancer with tamoxifen and one pulmonary embolism with placebo. CONCLUSION: Tamoxifen at 5 mg/d for 3 years can halve the recurrence of breast intraepithelial neoplasia with a limited toxicity, which provides a new treatment option in these disorders.

Background: Tamoxifen reduces the risk of breast cancer in women at high risk for the disease but increases the risk for endometrial tumors and venous thromboembolisms, possibly in a dose-dependent fashion. We compared the effects of tamoxifen at 1 mg/day and 5 mg/day with those of the standard dose of 20 mg/day on breast cancer proliferation using a surrogate endpoint marker (Ki-67 expression) and blood biomarkers associated with breast cancer, cardiovascular disease, and bone fracture risk. Methods: We randomly assigned 120 women with estrogen receptor (ER)-positive breast cancer to tamoxifen at 1, 5, or 20 mg/day for 4 weeks. Expression of the tumor proliferation marker Ki-67 and of biomarkers of breast cancer (insulin-like growth factor-I, sex hormone-binding globulin), cardiovascular disease (cholesterol, triglycerides, ultrasensitive C-reactive protein, fibrinogen, antithrombin-III), and bone fracture (type I collagen C-telopeptide) risk were determined before (baseline) and after treatment. All levels were compared with those in two nonrandomized control groups (34 women with ER-negative breast cancer and 29 additional women with ER-positive breast cancer). Data were analyzed by analysis of covariance. All statistical tests were two-sided. Results: Expression of Ki-67 decreased in all three tamoxifen groups, with no difference in the magnitude of reduction among groups (P = .81). Relative to baseline, Ki-67 expression decreased by a median of 15.0% (95% confidence interval = 0.0% to 24.1%) among the tamoxifen groups but increased by 12.8% (95% confidence interval = 0.0% to 19.6%) among the nonrandomized control groups. Several blood biomarkers showed dose–response relationships with tamoxifen, including decreased insulin-like growth factor-I, increased sex hormone-binding globulin, and decreased low-density lipoprotein-cholesterol, ultrasensitive C-reactive protein, fibrinogen, and antithrombin-III levels. Conclusions: The effects on Ki-67 expression of lower doses of tamoxifen were comparable to those achieved with the standard dose, although the effects on blood biomarkers were variable. The effects of lower doses of tamoxifen should be assessed further in randomized trials.

Background— Tamoxifen, a selective estrogen-receptor modulator, increases venous thromboembolic events (VTE), but the factors explaining this risk are unclear. Atherosclerosis may induce VTE, or the 2 conditions may share common risk factors. We assessed the effect of tamoxifen on VTE in a breast cancer prevention trial and studied its association with risk factors for VTE. Methods and Results— The incidence of VTE was studied in 5408 hysterectomized women randomly assigned to tamoxifen 20 mg/d or placebo for 5 years. There were 28 VTEs on placebo and 44 on tamoxifen therapy (hazard ratio [HR]=1.63; 95% confidence interval [CI], 1.02 to 2.63), 80% of which were superficial phlebitis, accounting for all of the excess due to tamoxifen within 18 months from randomization. Compared with placebo, the risk of VTE on tamoxifen was higher in women aged 55 years or older, women with a body mass index ≥25 kg/m ² , elevated blood pressure, total cholesterol ≥250 mg/dL, current smoking, and a family history of coronary heart disease (CHD). Of the 685 women with a CHD risk score ≥5 who entered the trial, 1 in the placebo arm and 13 in the tamoxifen arm developed VTE (log-rank P =0.0013). In multivariate regression analysis, age ≥60 years, height ≥165 cm, and diastolic blood pressure ≥90 mm Hg had independent detrimental effects on VTE risk during tamoxifen therapy, whereas transdermal estrogen therapy concomitant with tamoxifen was not associated with any excess of VTE (HR=0.64; 95% CI, 0.23 to 1.82). Conclusions— Women with conventional risk factors for atherosclerosis have a higher risk of VTE during tamoxifen therapy. This information should be incorporated into counseling women on its risk-benefit ratio, particularly in the prevention setting.

Clinical trials frequently include multiple end points that mature at different times. The initial report, typically based on the primary end point, may be published when key planned co-primary or secondary analyses are not yet available. Clinical Trial Updates provide an opportunity to disseminate additional results from studies, published in JCO or elsewhere, for which the primary end point has already been reported. PURPOSE: Five-year data of the phase III trial TAM-01 showed that low-dose tamoxifen at 5 mg once daily administered for 3 years in women with intraepithelial neoplasia (IEN) reduced by 52% the recurrence of invasive breast cancer or ductal carcinoma in situ (DCIS), without additional adverse events over placebo. Here, we present the 10-year results. METHODS: We randomly assigned 500 women with breast IEN (atypical ductal hyperplasia, lobular carcinoma in situ [LCIS], or hormone-sensitive or unknown DCIS) to low-dose tamoxifen or placebo after surgery with or without irradiation. The primary end point was the incidence of invasive breast cancer or DCIS. RESULTS: The TAM-01 population included 500 women (20% atypical ductal hyperplasia, 11% LCIS, and 69% DCIS). The mean (±SD) age at the start of treatment was 54 ± 9 years, and 58% of participants were postmenopausal. After a median follow-up of 9.7 years (IQR, 8.3-10.9 years), 66 breast cancers (15 in situ; 51 invasive) were diagnosed: 25 in the tamoxifen group and 41 in the placebo group (annual rate per 1,000 person-years, 11.3 with tamoxifen v 19.5 with placebo; hazard ratio [HR], 0.58; 95% CI, 0.35 to 0.95; log-rank P = .03). Most recurrences were invasive (77%) and ipsilateral (59%). Regarding contralateral breast cancer incidence, there were six events in the tamoxifen arm and 16 in the placebo arm (HR, 0.36; 95% CI, 0.14 to 0.92; P = .025). The number needed to be treated to prevent one case of breast event with tamoxifen therapy was 22 in 5 years and 14 in 10 years. The benefit was seen across all patient subgroups. There was a significant 50% reduction of recurrence with tamoxifen in the DCIS cohort, which represents 70% of the overall population (HR, 0.50; 95% CI, 0.28 to 0.91; P = .02). No between-group difference in the incidence of serious adverse events was reported during the prolonged follow-up period. CONCLUSION: Tamoxifen 5 mg once daily for 3 years significantly prevents recurrence from noninvasive breast cancer after 7 years from treatment cessation without long-term adverse events.

Purpose: Tamoxifen and fenretinide are active in reducing premenopausal breast cancer risk and work synergistically in preclinical models. The authors assessed their combination in a two-by-two biomarker trial. Patients and Methods: A total of 235 premenopausal women with pT1mic/pT1a breast cancer (n = 21), or intraepithelial neoplasia (IEN, n = 160), or 5-year Gail risk ≥ 1.3% (n = 54) were randomly allocated to either tamoxifen 5 mg/d, fenretinide 200 mg/d, their combination, or placebo. We report data for plasma insulin-like growth factor I (IGF-I), mammographic density, uterine effects, and breast neoplastic events after 5.5 years. Results: During the 2-year intervention, tamoxifen significantly lowered IGF-I and mammographic density by 12% and 20%, respectively, fenretinide by 4% and 10% (not significantly), their combination by 20% and 22%, with no evidence for a synergistic interaction. Tamoxifen increased endometrial thickness principally in women becoming postmenopausal, whereas fenretinide decreased endometrial thickness significantly. The annual rate of breast neoplasms (n = 48) was 3.5% ± 1.0%, 2.1% ± 0.8%, 4.7% ± 1.3%, and 5.2% ± 1.3% in the tamoxifen, fenretinide, combination, and placebo arms, respectively, with hazard ratios (HRs) of 0.70 (95% CI, 0.32 to 1.52), 0.38 (95% CI, 0.15 to 0.90), and 0.96 (95% CI, 0.46 to 1.99) relative to placebo (tamoxifen × fenretinide adverse interaction P = .03). There was no clear association with tumor receptor type. Baseline IGF-I and mammographic density did not predict breast neoplastic events, nor did change in mammographic density. Conclusion: Despite favorable effects on plasma IGF-I levels and mammographic density, the combination of low-dose tamoxifen plus fenretinide did not reduce breast neoplastic events compared to placebo, whereas both single agents, particularly fenretinide, showed numerical reduction in annual odds of breast neoplasms. Further follow-up is indicated.