In a study of 77 patients with advanced melanoma treated with a combination of CTLA-4 and PD-1 blocking, analysis of blood, tumor, and gut microbes showed that irAEs were not associated with the α diversity of the microbiome but were associated with the baseline abundance of specific bacterial taxa, including Bacteroides intestinalis and Intestinibacter bartlettii. This evidence concerns the gene CTLA4 and neoplasm.