FASTing-like Approach and Maintenance IMMunotherapy in ES-SCLC Patients Not Progressing on Chemoimmunotherapy Induction

Inclusion Criteria: * Participants who are able to comply with the requirements and restrictions listed in the Informed Consent Form and the study protocol (there is no separate Informed Consent Form for entering the maintenance phase) * Signature of the informed consent form for those patients who have not previously participated to the induction phase of the study * Age greater than or equal to 18 years and less than or equal to 75 years * Willingness and ability to comply with the prescribed cyclic, 5-day calorie restriction regimen, the scheduled visits, treatment plans, laboratory tests and other procedures * Histologically or cytologically confirmed diagnosis of small-cell lung cancer (SCLC). * Radiological evidence of extensive-stage (ES) disease. * Patient has available archival tumor tissue. Patients for whom only cytological material is available may be enrolled only if cytoincluded material is available. * Patients must have received a first-line, chemoimmunotherapy induction with 4 triweekly cycles of atezolizumab plus carboplatin and etoposide, with the last cycle of induction chemoimmunotherapy administered not more than six weeks before the initiation of experimental maintenance treatment. Delays between cycles of chemoimmunotherapy due to the occurrence of AEs or other medical reasons are considered acceptable, provided that a total number of 4 cycles of chemoimmunotherapy with atezolizumab plus carboplatin and etoposide have been administered, and that there is no radiological evidence of disease progression. * Radiological evidence of nonprogressive disease after chemoimmunotherapy induction with 4 triweekly cycles of atezolizumab plus carboplatin and etoposide. * Patients with a history of treated CNS metastases are eligible, if there is no evidence of interim progression between the completion of CNS-directed therapy and the experimental maintenance treatment initiation, and if CNS metastases are asymptomatic. * An Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1 or 2. * Presence of an adequate bone marrow and organ function * Female patients of childbearing potential must agree to abstinence from heterosexual intercourse or to use two highly effective methods of contraception throughout the study and for at least six months after the end of the maintenance treatment. * 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 * Male patients must agree to abstinence from heterosexual intercourse or to use two highly effective methods of contraception during sexual contact with a female with childbearing potential throughout the study and for at least six months after the end of the maintenance treatment. Exclusion Criteria: * Prior systemic treatment for ES SCLC, with the exception for first-line chemoimmunotherapy induction with 4 triweekly cycles of atezolizumab plus carboplatin and etoposide. Patients who received prior concurrent chemoradiotherapy for limited-stage (LS) disease may be enrolled if concurrent chemoradiotherapy was concluded at least three months before enrollment. * Patient has not available archival tumor tissue or has only cytological material without cytoincluded material available. * The patient has not recovered from immune-related AEs of grade 2 or higher from the induction phase with atezolizumab plus carboplatin and etoposide. Patients with adequately-treated, controlled, immune-related skin rash of grade 2 or adequately-treated, controlled, endocrinopathies of grade 2 on replacement therapy can be enrolled. * Body mass index (BMI) \< 19 kg/m2. * Unintentional 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 unintentional weight loss ≥ 10% in the previous 3 months, unless the patient has a BMI \> 25 kg/m2 and weight loss has been lower than 15% at the time of the enrollment in the study. In all cases, weight must have been stable for at least one month before study enrollment. * Baseline plasma glucose concentration ≤ 60 mg/dL (after at least 8 hours fasting) * Diagnosis of any other malignancy within 2 years prior to enrollment, with the exception of adequately treated in-situ bladder cancer, in-situ carcinoma of the cervix, uteri, non-melanomatous skin cancer, ductal in-situ breast cancer, thyroid cancer or early-stage prostate cancer (all treatment of which should have been completed at least 6 months prior to enrollment) * Asymptomatic and untreated, symptomatic or unstable CNS metastases as determined by CT-scan or MRI evaluation during screening and/or prior radiographic assessments. * Spinal cord compression not definitively treated with surgery and/or radiation or previously diagnosed and treated but not clinically stable for ≥ 4 weeks prior to the experimental maintenance treatment initiation. * Leptomeningeal disease. * Uncontrolled pleural effusion, pericardial effusion, or ascites requiring recurrent drainage procedures (once monthly or more frequently). * History of alcohol abuse. * Active pregnancy or breastfeeding. * 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 experimental treatment initiation. * Serious infections in the previous 4 weeks before the experimental maintenance treatment initiation. * Active autoimmune diseases requiring systemic treatments (e.g., systemic steroids or immunosuppressants). * Other medical conditions requiring active chronic therapy with systemic steroids at a dose ≥ 10 mg per day of prednisone or equivalent or other immunosuppressive medications within 14 days before the experimental maintenance treatment initiation. * Adrenal replacement steroid doses ≥ 10 mg per day of prednisone or equivalent are permitted in the absence of active autoimmune disease * Diagnosis of type 1 or 2 diabetes mellitus requiring pharmacologic therapy (including, but not limited to, insulin and secretagogues). A diagnosis of type 2 diabetes mellitus not requiring insulin and secretagogues on the judgment of a diabetologist and treated with metformin or alpha-glucosidase inhibitors (e.g., acarbose) is compatible with patient enrollment in the trial. * Active gastric or intestinal ulcerative disease, uncontrolled nausea, vomiting, diarrhea, malabsorption syndrome, small intestine resection. * 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 maintenance treatment. 2. congestive heart failure NYHA class III-IV. 3. 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 arrhythmias. * Previous episodes of symptomatic hypotension leading to loss of consciousness. * Medical or psychiatric comorbidities rendering the patient not candidate to the clinical trial, according to the investigator's judgement. * 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.