CD274 and digestive system neoplasm: The gut microbiota can affect the antitumor immune response of cancer through innate and adaptive immunity, and increasing evidence indicates that the diversity of gut microbiota is related to the clinical efficacy of anti-PD-1/PD-L1 monotherapy in melanoma, non-small cell lung cancer, gastrointestinal tumors, and renal cell carcinoma, and may become potential biomarkers for the prediction of immunotherapy efficacy (Gopalakrishnan et al., 2018a; Zheng et al., 2019; Jin et al., 2019; Routy et al., 2018; Temraz et al., 2019).