Calorie Restriction With or Without Metformin in Triple Negative Breast Cancer

Inclusion Criteria: * Patients eligible for inclusion in this study must meet all of the following criteria: 1. Female sex 2. Age ≥ 18 and ≤ 75 years. 3. Evidence of a personally signed and dated informed consent document (ICD) indicating that the patient has been informed of all pertinent aspects of the study before enrollment 4. Willingness and ability to comply with the prescribed FMD regimen, metformin intake, the scheduled visits, treatment plans, laboratory tests and other procedures. 5. Histologically confirmed diagnosis of invasive TNBC candidate to neoadjuvant chemotherapy and subsequent curative surgery. On the basis of International Guidelines, TNBC is defined by absent or minimal (\<1%) expression of oestrogen and progesterone receptors at IHC, and absence of HER2 over-expression or amplification, as defined as an IHC score of 0, 1+, or an IHC score of 2+ with in situ hybridization (ISH) analysis excluding HER2 gene amplification. 6. Patients with localized disease (clinical stage I-III according to TNM). Patients with Stage I TNBC will be included only if the primary tumor is at least 10 mm in greatest dimension (clinical T1c as determined through baseline MRI assessment). 7. Presence of an Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1. 8. Presence of adequate bone marrow and organ function as defined by the following laboratory values: 1. ANC ≥ 1.5 x 103/l 2. platelets ≥ 100 x 103/l 3. hemoglobin ≥ 9.0 g/dl 4. calcium (corrected for serum albumin) within normal limits or ≤ grade 1 according to NCI-CTCAE version 5.0 if not clinically significant 5. potassium within the normal limits, or corrected with supplements 6. creatinine \< 1.5 ULN 7. blood uric acid \< 10 mg/dl 8. ALT and AST ≤ 2 x ULN 9. total bilirubin \< 1.5 ULN except for patients with Gilbert syndrome who may only be included if the total bilirubin is \< 3.0 x ULN or direct bilirubin \< 1.5 x ULN 10. Fasting glucose ≤ 250 mg/dl. 9. Female patients of childbearing potential must agree to sexual abstinence or to use two highly effective methods of contraception throughout the study and for at least six months after the end of the FMD. Abstinence is only acceptable if it is in line with the preferred and usual lifestyle of the patient. Examples of contraceptive methods with a failure rate of \< 1% per year include tubal ligation, male sterilization, hormonal implants, established, proper use of combined oral or injected hormonal contraceptives, and certain intrauterine devices. Alternatively, two methods (e.g., two barrier methods such as a condom and a cervical cap) may be combined to achieve a failure rate of \< 1% per year. Barrier methods must always be supplemented with the use of a spermicide. A patient is of childbearing potential if, in the opinion of the Investigator, she is biologically capable of having children and is sexually active. 10. Female patients are not of childbearing potential if they meet at least one of the following criteria: 1. Have undergone a documented hysterectomy and/or bilateral oophorectomy 2. Have medically confirmed ovarian failure 3. Achieved post-menopausal status, defined as: ≥ 12 months of non-therapy-induced amenorrhea or surgically sterile (absence of ovaries) and have a serum FSH level within the laboratory's reference range for postmenopausal females. Exclusion Criteria: * Patients eligible for this study must not meet any of the following criteria: 1. Prior systemic treatment for breast cancer or other malignancies within 5 years of treatment enrollment. 2. Prior treatment with anthracyclines 3. Diagnosis of other malignancies in advanced stages (unresectable, locally advanced or metastatic), or that required systemic (neo)adjuvant chemotherapy in the previous 5 years. Other malignancies diagnosed more than 5 years before the diagnosis of breast cancer must have been radically treated without evidence of relapse at the moment of patient enrollment in the trial. 4. Body mass index (BMI) \< 20 kg/m2. 5. History of alcohol abuse. 6. Non-intentional weight loss ≥ 5% in the previous 3 months, unless the patient has a BMI \> 22 kg/m2 and weight loss has been lower than 10% at the time of enrollment in the study; or non-intentional weight loss of ≥ 10% in the previous 3 months, unless the patients has a BMI \> 25 kg/m2 and weight loss has been lower than 15% at the time of the enrollment in the study. In both cases, weight must have been stable for at least one month before study enrollment. 7. Active pregnancy or breast feeding. 8. Known active B or C hepatitis or human immunodeficiency virus (HIV) infection, or occasional finding of active hepatitis B/C infection during screening tests before chemotherapy initiation, as defined as positive polymerase chain reaction (PCR) testing for HBV-DNA and HCV-RNA and qualitative PCR for HIV-RNA, or requiring active treatment at study enrollment. 9. Serious infections in the previous 4 weeks before the FMD initiation, including, but not limited to, potential hospitalizations for complications of infections, bacteriemia or serious pneumonitis. 10. Active autoimmune diseases requiring systemic treatments (e.g. systemic steroids or immune suppressants). 11. Active chronic therapy with systemic steroids at a dose ≥ 10 mg per day of prednisone or equivalent at study enrollment. 12. Known recent diagnosis of hypothyroidism requiring systemic replacement hormonal therapy and without stabilization of hormonal profile (fT3, fT4 and TSH within the normal range). 13. Diagnosis of type 1 or 2 diabetes mellitus requiring pharmacologic therapy (including, but not limited to, insulin, secretagogues and metformin). A diagnosis of type 2 diabetes mellitus not requiring pharmacological treatments based on the judgment of a diabetologist, is compatible with patient enrollment in the trial. 14. Active gastric or intestinal ulcerative disease, uncontrolled nausea, vomiting, diarrhea, malabsorption syndrome, small intestine resection. 15. Anamnesis of clinically significant heart disease including: 1. angina pectoris, coronary bypass, symptomatic pericarditis, myocardial infarction in the previous 12 months from the beginning of experimental therapy; 2. congestive heart failure (NYHA III-IV). 16. Anamnesis of clinically meaningful cardiac arrhythmias, such as ventricular tachycardia, chronic atrial fibrillation, complete bundle branch block, high grade atrio-ventricular block like bi-fascicular block, type II Mobitz and third grade atrio-ventricular block, nodal arrhythmias, supra-ventricular arrhythmia. 17. Left ventricular ejection fraction lower than 50% at the cardiac scan with radionuclides or at echocardiography. 18. Previous episodes of symptomatic hypotension leading to loss of consciousness. 19. Baseline plasma fasting glucose ≤ 60 mg/dL. 20. Medical or psychiatric comorbidities rendering the patient not candidate to the clinical trial, according to the investigator's judgement. 21. Other cardiac, liver, lung or renal comorbidities, not specified in the previous inclusion or exclusion criteria, but potentially exposing the patient to a high risk of lactic acidosis.