The METTEN trial evaluated the addition of metformin (850 mg twice daily) to neoadjuvant chemotherapy and trastuzumab in women with early HER2-positive breast cancer and found a numerically higher pathological complete response (pCR) rate in the metformin arm (65.5%) compared to the control (58.6%), though this difference was not statistically significant (p = 0.589), and the regimen was generally well tolerated [118]. The gene discussed is ERBB2; the disease is breast cancer.