Impact of Metformin Use on Clinical and Pathological Outcomes in Breast Cancer Patients With Type 2 Diabetes

Breast cancer is the most common malignancy in women, and its incidence is increasing worldwide. Type 2 diabetes mellitus (T2DM) is a significant comorbidity in patients with breast cancer that negatively affects prognosis. Metformin, a first-line antidiabetic drug, has been suggested to possess antineoplastic properties. This study investigated the effects of metformin on the demographic characteristics, pathological parameters, treatment response, and prognosis of breast cancer patients with T2DM in an Iranian population.

A retrospective cross-sectional study was conducted on 104 patients with breast cancer and T2DM at the Velayat Educational and Therapeutic Center, Qazvin, Iran, from 2019 to 2023. The patients were categorized into two groups: metformin users (n = 46) and non-users (n = 58). Data on demographic characteristics, disease stage, lymph node involvement, hormone receptor status, treatment response, prognosis, recurrence, and metastasis were collected. Statistical analyses were performed using SPSS version 25, with significance set at p < 0.05. Unadjusted and adjusted logistic regression analyses were performed to identify independent predictors of prognosis.

The mean disease duration was significantly shorter in the metformin group than in the non-metformin group (p = 0.036). A significant difference was observed in the stage of disease (p = 0.003), with metformin users more frequently presenting at earlier stages. Lymph node involvement was significantly lower in the metformin group (p = 0.008). Patients using metformin showed significantly better treatment response (p = 0.028) and prognosis (p = 0.009). However, no significant differences were observed in the estrogen receptor (ER) status (p = 0.293), human epidermal growth factor receptor 2 (HER2) status (p = 0.762), metastasis (p = 0.249), or recurrence rates (p = 0.770). After adjustment, disease duration, HER2 status, and metformin use remained independently associated with prognosis.

Metformin use in breast cancer patients with T2DM is associated with lower disease stage, fewer involved lymph nodes, improved treatment response, and better prognosis. These findings suggest that metformin may play a beneficial role in breast cancer progression and treatment outcomes. Further prospective studies are warranted to confirm these results in a clinical setting and to elucidate the underlying mechanisms.