ESR1 and neoplasm: After adjusting for age, BMI, tumor size, lymph node metastasis, ER, PR, and HER2-neu status, and systemic treatment, patients who did not receive treatment with metformin tended to have shorter OS (HR 1.87; 95 % CI 1.25 to 2.81), CSS (HR 1.85; 95 % CI 1.17 to 2.92) and DFS (HR 1.59; 95 % CI 1.06 to 2.39) than those of the metformin group (Fig. 4, Table 3).