A presurgical phase II study on activity of metformin on breast cancer cell proliferation

INTERVENTION: 1. Patients are randomized in a double blind fashion to metformin (850 mg bid) or placebo and treated for 4 weeks 2. During the first three days of treatment patients are asked to take half dose (850 mg/die) in order to adapt to gastrointestinal symptoms CONDITION: Breast cancer ; Cancer ; Malignant neoplasm of breast PRIMARY OUTCOME: 1. The short‐term response in the proliferative antigen Ki‐67 LI, which is increasingly being used to screen active drugs in breast cancer because of its prognostic value and its postulated role in predicting the efficacy of anti cancer drugs; 2. Percent change in Ki‐67 LI between pretreatment biopsy and post‐treatment surgical specimen SECONDARY OUTCOME: 1. Effect of metformin on Ki‐67 based on change in Homa index; 2. Effect of metformin on circulating biomarkers (lipid profile, CRP, testosterone, adypokines, C‐peptide, insulin, glycemia); 3. Evaluation of the antiproliferative activity of metformin on hyperplastic, dysplastic and malignant breast tissue INCLUSION CRITERIA: 1. Age >18 years 2. Performance status=0 (Southwest Oncology Group [SWOG]) 3. Histologically‐confirmed breast cancer not candidate to neoadjuvant therapy, no prior treatment for breast cancer 4. Signed informed consent