However, most of the in-vitro models showing anti-HER2 activity of metformin used drug concentrations in the millimolar range, far higher than reported plasma metformin concentrations seen in diabetic patients treated with metformin [27, 31, 32], thereby leaving unanswered the question of whether metformin would have a clinical effect in patients suffering from HER2-positive BC. The gene discussed is ERBB2; the disease is breast cancer.