CA15-3/MUC1 in CCTG MA-32 (NCT01101438): A phase III RCT of the effect of metformin vs. placebo on invasive disease free and overall survival in early stage breast cancer (BC).

557Background: The diabetes drug metformin may improve BC outcomes through enhanced obesity-related physiology or direct anti-tumor effects. We studied the effect of metformin on CA15-3 (the soluble moiety of the MUC1 protein), a marker associated with BC prognosis that also has mitogenic and metabolic effects that favor tumorigenesis. Methods: 3,256 women with T1-3, N0-3, M0 BC who had completed standard therapy (ongoing hormone therapy permitted) provided fasting blood (stored at -80C) at baseline and 6 months. CA15-3 and insulin were measured by Roche ECLIA; leptin, and hs-CRP by Luminex Milliplex MAP and Roche ITA. Spearman coefficients were calculated and comparisons analyzed using Wilcoxon signed rank test and multivariable linear regression models. Tests were two-sided. Results: Mean age was 52.3 and BMI 28.6 kg/m2. Tumor and treatment characteristics were balanced between arms (overall: T2/3 in 59.8%, N +ve in 52.9%, grade 1/2/3 in 9.1%/35.3%/54.4%, ER+ in 69.6%, HER2+ in 17.1%; 50.4% underwent ma...