Effect of Metformin Versus Placebo on New Primary Cancers in Canadian Cancer Trials Group MA.32: A Secondary Analysis of a Phase III Randomized Double-Blind Trial in Early Breast Cancer

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 coprimary 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.Metformin has been associated with lower cancer risk in epidemiologic and preclinical research. In the MA.32 randomized adjuvant breast cancer trial, metformin (v placebo) did not affect invasive disease-free or overall survival. Here, we report metformin effects on the risk of new cancer. Between 2010 and 2013, 3,649 patients with breast cancer younger than 75 years without diabetes with high-risk T1-3, N0-3 M0 breast cancer (any estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2) were randomly assigned to metformin 850 mg orally twice a day or placebo twice a day for 5 years. New primary invasive cancers (outside the ipsilateral breast) developing as a first event were identified. Time to events was described by the competing risks method; two-sided likelihood ratio tests adjusting for age, BMI, smoking, and alcohol intake were used to compare metformin versus placebo arms. A total of 184 patients developed new invasive cancers: 102 metformin and 82 placebo, hazard ratio (HR), 1.25; 95% CI, 0.94 to 1.68; P = .13. These included 48 contralateral invasive breast cancers (27 metformin v 21 placebo), HR, 1.29; 95% CI, 0.72 to 2.27; P = .40 and 136 new nonbreast primary cancers (75 metformin v 61 placebo), HR, 1.24; 95% CI, 0.88 to 1.74; P = .21. Metformin did not reduce the risk of new cancer development in these nondiabetic patients with breast cancer.

Effect of Metformin vs Placebo on Invasive Disease-Free Survival in Patients With Breast Cancer: The MA.32 Randomized Clinical Trial

Importance

Metformin, a biguanide commonly used to treat type 2 diabetes, has been associated with potential beneficial effects across breast cancer subtypes in observational and preclinical studies.

Objective

To determine whether the administration of adjuvant metformin (vs placebo) to patients with breast cancer without diabetes improves outcomes.

Design, Setting, and Participants

MA.32, a phase 3 randomized, placebo-controlled, double-blind trial, conducted in Canada, Switzerland, US, and UK, enrolled 3649 patients with high-risk nonmetastatic breast cancer receiving standard therapy between August 2010 and March 2013, with follow-up to October 2020.

Interventions

Patients were randomized (stratified for hormone receptor [estrogen receptor and/or progesterone receptor {ER/PgR}] status, positive vs negative; body mass index, ≤30 vs >30; human epidermal growth factor receptor 2 [ERBB2, formerly HER2 or HER2/neu], positive vs negative; and any vs no chemotherapy) to 850 mg of oral metformin twice a day (n = 1824) or oral placebo twice a day (n = 1825) for 5 years.

Main Outcomes and Measures

The primary outcome was invasive disease-free survival in hormone receptor-positive breast cancer. Of the 8 secondary outcomes, overall survival, distant relapse-free survival, and breast cancer-free interval were analyzed.

Results

Of the 3649 randomized patients (mean age, 52.4 years; 3643 women [99.8%]), all (100%) were included in analyses. After a second interim analysis, futility was declared for patients who were ER/PgR-, so the primary analysis was conducted for 2533 patients who were ER/PgR+. The median duration of follow-up in the ER/PgR+ group was 96.2 months (range, 0.2-121 months). Invasive disease-free survival events occurred in 465 patients who were ER/PgR+. The incidence rates for invasive disease-free survival events were 2.78 per 100 patient-years in the metformin group vs 2.74 per 100 patient-years in the placebo group (hazard ratio [HR], 1.01; 95% CI, 0.84-1.21; P = .93), and the incidence rates for death were 1.46 per 100 patient-years in the metformin group vs 1.32 per 100 patient-years in the placebo group (HR, 1.10; 95% CI, 0.86-1.41; P = .47). Among patients who were ER/PgR-, followed up for a median of 94.1 months, incidence of invasive disease-free survival events was 3.58 vs 3.60 per 100 patient-years, respectively (HR, 1.01; 95% CI, 0.79-1.30; P = .92). None of the 3 secondary outcomes analyzed in the ER/PgR+ group had statistically significant differences. Grade 3 nonhematological toxic events occurred more frequently in patients taking metformin than in patients taking placebo (21.5% vs 17.5%, respectively, P = .003). The most common grade 3 or higher adverse events in the metformin vs placebo groups were hypertension (2.4% vs 1.9%), irregular menses (1.5% vs 1.4%), and diarrhea (1.9% vs 7.0%).

Conclusions and Relevance

Among patients with high-risk operable breast cancer without diabetes, the addition of metformin vs placebo to standard breast cancer treatment did not significantly improve invasive disease-free survival.

Trial Registration

ClinicalTrials.gov Identifier: NCT01101438.

Abstract GS1-08: CCTGMA.32, a phase III randomized double-blind placebo controlled adjuvant trial of metformin (MET) vs placebo (PLAC) in early breast cancer (BC): Results of the primary efficacy analysis (clinical trials.gov NCT01101438)

Background: MET has been associated with beneficial anti-cancer effects in epidemiologic and preclinical research. It may act indirectly by reversing obesity associated physiologic changes or directly via mitochondrial mediated effects on LKB1/AMPK/mTOR and other mechanisms. MA.32 investigated the effect of MET vs PLAC (in addition to standard therapy) on adjuvant BC outcomes. Design: Randomized, placebo-controlled double-blind Phase III clinical trial conducted within the NCI US National Clinical Trials Network, NCRI (UK) BG, IBCSG. Methods: Between 2010-2013 BC patients < 75 yo without diabetes (DM) with high risk T1-3, N0-3 M0 BC regardless of ER, PgR, HER2 and with adequate cardiac, renal and hepatic function were randomized (stratified for ER/PgR + vs -, BMI < vs > 30 kg/m2, HER2 +ve vs -ve, any vs no chemo) within 1 year of BC diagnosis to MET 850 mg po bid or PLAC bid for 5 years. Dose was reduced for toxicity with re-escalation when possible. Subjects were followed for Invasive Disease-Free Survival (IDFS primary outcome; events included invasive local/regional recurrences, distant recurrences, new ipsilateral/contralateral invasive BCs, new non-breast primary cancers, any death), Overall Survival (OS), Distant Relapse Free Survival (DRFS), BC Specific Survival (BCSS), BC Free Interval (BCFI), contralateral BC and cardiovascular (CV) events/new DM. 3582 subjects were required for 80% power to detect HR 0.76 (431 events). In 2011, entry was restricted to higher risk BC, leading to 80% power to detect HR 0.785 (544 events). In 2016, after the 2nd interim analysis at 29.5 months median F/U, the DSMB recommended (i) the intervention be continued with primary analysis triggered at 544 events be conducted in ER/PgR +ve (any HER2) subjects only and (ii) ER/PgR -ve subjects stop study drug for futility but blinding and follow-up continue. In 2021, a time driven analysis in ER/PgR +ve BC was approved (465 events providing 80% power to detect the original HR 0.76). Time to event survival described by the Kaplan-Meier method. Two-sided log-rank tests adjusting for stratification factors were primarily used to compare IDFS between arms. Cox proportional hazards models were used to identify and adjust for factors significantly related to IDFS. Results: 3649 subjects were enrolled. In the 2533 ER/PgR +ve subjects included in the primary analysis, baseline mean (± SD) age was 52.7 (±9.9 yrs); mean BMI 28.8 (±6.4) kg/m2. Baseline tumor characteristics were balanced: T stage 1/2/3/4 = 832/1351/349/1; N stage 0/1/2/3 = 964/1097/449/23; HER2+ 429. 1901 (75%) received XRT. 2150 (84.9%) received (neo)adj chemo, 2223 (87.8%) (neo)adj hormones and 434 (17.1%) HER2 targeted therapy. Any Grade ≥ 3 toxicity was similar in MET and PLAC arms (21.7% and 18.7%, P = 0.06). Median follow-up was 96.2 (range 0.2-121.0) months with 465 IDFS events (234 MET, 231 PLAC, 76% due to BC). Efficacy results are shown below.

MET vs PLACMET vs PLACIDFSOSPopulation Included# subjectsHR (95% CI)HR (95% CI)PRIMARY ANALYSISER/PgR +ve (any HER2)*25331.01 (0.84-1.21). P=0.920.89 (0.64-1.23). P=0.46ER/PgR -ve (any HER211161.01 (0.79-1.30. P=0.92)0.89 (0.64-1.23). P=0.46Exploratory. AnalysisHER2 +ve (any ER/PgR)6200.64 (0.43-0.95. P=0.0260.53 (0.30-0.98. P=0.0398**in ER/PgR pos BC HRs were similar for BCFI, DRFS, BCSS (ranging from 0.98-1.09)Conclusions: MET did not improve IDFS or other BC outcomes in ER/PgR positive or ER/PgR negative BC and should not be used as adjuvant treatment. Exploratory findings suggesting benefit in HER2+ve BC should be further investigated. Funded by: CCSRI, NCI (US), CBCF, BCRF, CRUK, Hold’Em for Life Charity, Apotex (Canada)

Citation Format: Pamela J. Goodwin, Bingshu E Chen, Karen A Gelmon, Timothy J Whelan, Marguerite Ennis, Julie Lemieux, Jennifer A Ligibel, Dawn L Hershman, Ingrid A Mayer, Timothy J Hobday, Judith M Bliss, Priya Rastogi, Manuela Rabaglio-Poretti, Som D. Mukherjee, Robert R Mackey, Vandana G Abramson, Conrad Oja, Robert Wesolowski, Alastair M Thompson, Daniel W Rea, Paul M Stos, Lois E Shepherd, Vuk Stambolic, Wendy R Parulekar. CCTGMA.32, a phase III randomized double-blind placebo controlled adjuvant trial of metformin (MET) vs placebo (PLAC) in early breast cancer (BC): Results of the primary efficacy analysis (clinical trials.gov NCT01101438) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr GS1-08.