Preliminary clinical findings showed that the signatures that reflect the composition and metabolites of the gut microbiota would impact the antitumor immune response in patients receiving ICIs, including anti-cytotoxic T-lymphocyte antigen 4 [CTLA-4] and anti-PD-1/PD-L1 antibodies, and have the potential to predict durable clinical responses in non-small cell lung cancer (NSCLC), renal cell carcinoma (RCC), and melanoma; however, the role of the microbiome in predicting the benefits from the ICIs remains unclear for gastrointestinal (GI) cancer [17,18,19,20,21]. The gene discussed is CTLA4; the disease is melanoma.