Among the patients who received chemotherapy and endocrine therapy, the non-metformin diabetic group had decreased DFS (HR 2.14; 95 % CI 1.14 to 4.04) compared with the metformin group, after adjusting for age, BMI, tumor size, lymph node metastasis, ER, PR and HER2. This evidence concerns the gene ESR1 and metastatic malignant neoplasm in the lymph nodes.