In a study of 1983 consecutive patients with HER2+ breast cancer treated between January 1 1998 and September 30 2010, it was shown that metformin (P = 0.041, HR = 0.52, 95% CI 0.28–0.97) and thiazolidinediones (P = 0.036; HR = 0.41, 95% CI 0.18–0.93) significantly lengthened survival and decreased breast cancer-specific mortality (P = 0.023, HR = 0.47, 95% CI 0.24–0.90 and P = 0.044, HR = 0.42, 95% CI 0.18–0.98, resp). The gene discussed is ERBB2; the disease is breast cancer.