Key clinical point: In patients with high-risk operable breast cancer (BC) and without diabetes, adding metformin to standard BC treatment did not improve the invasive disease-free survival (iDFS) rate, regardless of estrogen receptor/progesterone receptor (ER/PgR) status.
Major finding: The incidence rates of iDFS events were similar between the metformin and placebo groups in patients with ER/PgR+ BC (2.78 vs. 2.74 per 100 patient-years; P = .93) and ER/PgR− BC (3.58 vs. 3.60 per 100 patient-years; P = .92). Grade ≥3 nonhematological adverse events were more frequent in the metformin vs. placebo group (21.5% vs. 17.5%; P = .003).
Study details: Findings are from the phase 3 MA.32 study including 3649 patients with high-risk operable BC and without diabetes who were randomly assigned to receive metformin or placebo after undergoing complete resection.
Disclosures: This study was funded by the Canadian Cancer Society Research Institute and other sources. The authors declared serving on advisory boards, as consultants, or were employees or received grants, nonfinancial support, or travel expenses from several sources.
Source: Goodwin PJ et al. Effect of metformin vs placebo on invasive disease–free survival in patients with breast cancer: The MA.32 Randomized Clinical Trial. JAMA. 2022;327(20):1963–1973 (May 24). Doi: 10.1001/jama.2022.6147