LBA5002 Background: Active Surveillance (AS) involves vigilant monitoring of selected prostate cancer (PCa) patients, with radical treatment initiation upon significant disease progression. AS eligibility varies, generally including low-risk PCa men. Metformin, a widely-used oral hypoglycemic agent, is known for its excellent tolerability and efficacy in diabetes management. Extensive preclinical data suggested that metformin may slow PCa progression. The purpose of this study is to examine the effect of metformin on the rates of progression among men with low-risk localized PCa on AS. Methods: A randomized double blind placebo controlled trial was carried out in 14 centres across Canada.Eligible patients had biopsy-proven, low-risk, localized PCa diagnosed within the past 6 months, with a Gleason score of <6 observed in ≤1/3 of the total cores, less than 50% positivity in any one core, a PSA level of ≤10 ng/ml, and a clinical stage between T1c-T2a. Additionally, they chose active surveillance as their primary treatment. Subjects that met eligibility criteria were randomly assigned (1:1) to receive metformin 850 mg BID or placebo for 3 years. All patients underwent repeat prostate biopsy at 18 and 36 months. The primary endpoint indicated was time to progression, defined as the earliest occurrence of primary PCa therapy (e.g., prostatectomy, radiation, hormonal therapy) or pathological progression (>1/3 of total cores involved, at least 50% of any one core involved, or Gleason pattern 4 or higher). Results: In our cohort of 407 patients, 204 were administered metformin, and 203 received a placebo. The median age of the overall cohort was 63 years. Out of the total 407 patients, 141 experienced disease progression. There was no statistically significant difference in progression-free survival (PFS) observed between patients treated with metformin and those receiving placebo (p=0.63). Conclusions: Despite tantalizing preclinical and epidemiological data, metformin consumption does not alter rates of progression among men with low risk PCa on AS. Clinical trial information: NCT01864096 .