ERBB2 and breast cancer: Nonetheless, the post‐treatment serum levels of circulating H3K27me3 were significantly higher in nondiabetic HER2‐positive breast cancer patients who received diabetic doses of metformin (850 mg twice a day, which yielded median values of metformin concentrations in blood in the range of 5–20 μmol/L—unpublished observations) for 6 months, in addition to standard‐of‐care neoadjuvant treatment.