Metformin, placebo, and endocrine therapy discontinuation among participants in a randomized double-blind trial of metformin versus placebo in hormone receptor–positive early-stage breast cancer (CCTG MA32).

526 Background: The MA32 study (NCT01101438) investigated whether 5-years of metformin improves invasive disease-free survival in early-stage breast cancer (BC). Non-adherence to endocrine therapy (ET) and medications for chronic conditions is common, and increases with drug toxicity and polypharmacy. This secondary analysis evaluates rates and predictors of early discontinuation of metformin, placebo, and ET among …