Metformin and Nightly Fasting in Women With Early Breast Cancer

\- Primary Interim Objective The primary interim objective will be to assess the safety of the experimental intervention based on the frequency of occurrence of a Dose Limiting Toxicity (DLT) in the first 14 participants assigned to the experimental treatment arm. A DLT is defined as a hypoglycemic event requiring permanent discontinuation of study treatment or any grade 3 or greater adverse event (AE) possibly, probably, or definitely related to the study drug. Hypoglycemia AEs that require permanent discontinuation of study treatment are: * ≥ 1 grade 2 or higher neuroglycopenic symptoms and grade 2 hypoglycemia; * occurrence ≥ 3 times of grade 2 symptoms (≥ 2 autonomic or ≥ 1 neuroglycopenic symptoms) and grade 1 or higher hypoglycemia; * symptomatic or asymptomatic grade 3 hypoglycemia. In the first 14 participants enrolled in the experimental arm (combination of prolonged nightly fasting and Metformin Hydrochloride Extended-Release) we can accept at most 3 participants with a DLT. If 4 or more of the first 14 participants assigned to the treatment arm experience the above-mentioned DLTs, the trial will be definitively stopped. In order to early identify any DLT, participants will be instructed to contact study staff in case of occurrence of any symptoms regardless of their grade and a review of the occurrence of any AE will be performed every 10 days. The early detection of symptoms related to the study treatment will help us to avoid worsening of symptoms to grade 3 and thus prevent any DLT. Moreover, the glucose trends of the first 14 participants enrolled in the experimental arm will be downloaded and immediately evaluated to identify any asymptomatic hypoglycemia. Hypoglycemia will be assessed through the evaluation of glucose reports and fingersticks results in case of symptoms. \- Primary and Co-primary Objective We have recently shown that the combination of hypoglycemia and Metformin reduces tumor growth in animal models (1). Moreover, Metformin alone was able to reduce breast cancer cell proliferation in women with insulin resistance in a randomized presurgical trial (2,3). Breast carcinogenesis may be present in three components in surgical specimens and more rarely in biopsy specimens: invasive breast cancer (IBC), ductal carcinoma in situ (DCIS) and intraepithelial neoplasia (IEN), defined as atypical ductal hyperplasia (ADH) or atypical lobular hyperplasia (ALH) or lobular carcinoma in situ (LCIS). We propose to assess the effect of the combination of prolonged nightly fasting (≥16 hours) and Metformin Hydrochloride Extended-Release on the change of Ki67 labeling index (LI) in cancer tissue (IBC or DCIS, if IBC is absent) between pre-treatment biopsy and post treatment surgical specimen. As co-primary objective, we will also evaluate the difference in post-treatment Ki67 LI in cancer adjacent DCIS (in the presence of IBC), if present, or IEN (defined as ADH or ALH or LCIS) between the active treatment and the control group. IBC and DCIS strata will be based on the post-treatment pathology. If DCIS is the primary lesion because of the absence of invasive disease, adjacent IEN will be counted only if ADH/ALH/LCIS is present. The change (pre/post treatment) of Ki67 LI in IEN will be evaluated only if present in the pretreatment biopsy specimen. Secondary Objectives * to explore the effect of intervention on the change of expression of PP2A-GSK3ß-MCL-1 axis in pre-post treatment cancer tissue levels; * to measure the change in circulating biomarkers: HOMA index, Hb1Ac; * to measure the difference of cell death by IHC for M30 in post- treatment cancer samples between arms; * to measure the difference of pS6 by IHC in post- treatment cancer samples between arms; * to compare the area under the curve (AUC) of glucose levels between arms according to insulin resistance biomarker levels and WCRF score; * to assess safety and toxicities according to NCI-CTC AE v. 5.0. * Exploratory Objectives * to correlate a customized NGS mutational profile panel focused on ER+ve with the response of Ki67; * to measure the change in circulating biomarkers: highly sensitive CRP (hsCRP), C-peptide, IGF-I, IGFBP-1, IGFBP-3, free IGF-I, lipid profile, adipokines (leptin and adiponectin); * to correlate psychological distress, eating habits, tobacco and alcohol consumption with the response of Ki67 and insulin resistance biomarkers between arms; * to compare the slow ramp up schedule of metformin to the quick ramp up schedule to metformin in the treatment group on the area under the curve (AUC) of glucose levels