RecruitingDietary supplementDietary Interventions in Cancer Patients Treated With Immune Checkpoint InhibitorsThis pilot trial will study the potential impact of two distinct dietary interventions with sequential use of high-fermented foods and high-fiber supplements on the gut microbiome and antitumor immunity in patients with melanoma and non-small cell lung cancer (NSCLC) treated with immune checkpoint inhibitors. The trial aims to understand how dietary changes affect the composition and function of the gut microbiome, together with immunological and metabolomic markers in serum in patients with melanoma and NSCLC who are undergoing standard-of-care treatment with a PD-1/PD-L1 Inhibitors (neoadjuvant, adjuvant or consolidation)