Cyclic, 5-day calorie restriction is a safe metabolic intervention when combined with standard therapies in cancer patients, favorably reshaping peripheral blood and intratumor metabolism and immunity in a way that may improve the antitumor activity and efficacy of immunotherapy. The goal of this clinical trial is to test if combining cyclic, 5-day calorie restriction with atezolizumab maintenance in patients with ES SCLC achieving at least stable disease after four cycles of induction atezolizumab plus carboplatin and etoposide chemoimmunotherapy may increase the efficacy of a standard first-line, chemo-immunotherapy approach in terms of patient PFS. The main question it aims to answer is: • does the combination of cyclic, 5-day calorie restriction with triweekly atezolizumab increase the 6 months PFS rate, as evaluated from maintenance treatment initiation, compared to historical results with standard atezolizumab maintenance monotherapy in patients with ES SCLC non-progressive after four cycles of first-line chemo-immunotherapy induction with atezolizumab plus carboplatin and etoposide?

SCLC is the most aggressive and deadly subtype of lung cancer. Indeed, despite the novel treatment strategies, patients with ES SCLC still have a dismal prognosis. The most relevant therapeutic progress that occurred in the last decades in the treatment of this disease consists in the combination of immunotherapy (anti PD-L1 monoclonal antibodies) with standard cytotoxic chemotherapy as the first-line treatment. However, in clinical trials that led to the registration of currently used chemoimmunotherapy combination regimens, the addition of immunotherapy to chemotherapy approaches only led to a marginal increase in patient PFS and OS. Therefore, novel therapeutic strategies are needed to increase the efficacy of chemo-immunotherapy approaches. Pre-clinical and translational evidence suggests that patients with ES SCLC receiving anti-PD-1/PD-L1 agents may benefit from the combination of cyclic, short-term calorie restriction to immunotherapy both for reasons related to the metabolic vulnerabilities of SCLC cells (e.g., enhanced glycolysis) and their potential sensitivity to glucose-lowering strategies, and to the potential synergistic antitumor effects resulting from the combination of immunotherapy with cyclic calorie restriction. Based on these data, we design the FASTIMMUNE trial, a single center, open-label, single arm, phase II clinical study with a Simon's two-stage design. The study consists of 2 phases: an induction phase and an experimental maintenance treatment phase. Participants will undergo an experimental maintenance treatment with triweekly cycles of 5-day calorie restriction (on days -2 through 2 of each cycle) in combination with atezolizumab (at a dose of 1200 mg, administered intravenously on day 0 of each cycle) until the occurrence of unacceptable toxic effects, disease progression, consent withdrawal or patient death. Patients interrupting cyclic calorie restriction for any reason other than disease progression may continue the maintenance treatment with atezolizumab alone, if clinically indicated.