Preliminary efficacy results presented at the 2021 San Antonio Breast Cancer Symposium revealed that, irrespective of ER status, the HER2-positive population treated with metformin experienced benefits in terms of invasive disease-free survival (DFS) (HR = 0.64; 95% CI, 0.43–0.95) and OS (HR = 0.53; 95% CI, 0.3–0.98), a benefit not observed in HER2-negative breast cancer patients (see Table 3). Here, ERBB2 is linked to breast cancer.