Fig. 4
Challenges of ICI in SCLC. AÂ Historical timeline of ICI in the field of SCLC. The unprecedented results have been observed in several clinical trials undertaken in SCLC. BÂ Factors affecting ICI response in SCLC. Tumor-intrinsic factors: (1) Neoantigen depletion, (2) Defects in antigen presentation, (3) Genetic factors, (4) Aberration of IFN signaling; Tumor microenvironment: Tumor associated macrophages, MDSC, metabolites, T cells; Host: Metabolite, nutrients, gut microbiota. CÂ Major issues facing ICI treatment. The ICI challenges include four aspects: (1) Timing, (2) Biomarker response, (3) Combinational treatment, (4) Toxicity