This study provides a comprehensive analysis of the tumor microbiome in metastatic cancers, integrating metagenomics, genomics, and transcriptomics data from 4,160 metastatic tumor biopsies across 26 cancer types. The research identifies organ-specific tropisms of microbes, enrichments of anaerobic bacteria in hypoxic tumors, and associations between microbial diversity and tumor-infiltrating neutrophils. Notably, Fusobacterium abundance is associated with poor immunotherapy response in non-small cell lung cancer (NSCLC) patients. The study also reveals that immunotherapy can reshape the metastatic tumor microbiome, reducing bacterial diversity and affecting treatment outcomes. The findings highlight the potential of the tumor microbiome as a target for enhancing cancer therapy and provide a valuable resource for future research.This study provides a comprehensive analysis of the tumor microbiome in metastatic cancers, integrating metagenomics, genomics, and transcriptomics data from 4,160 metastatic tumor biopsies across 26 cancer types. The research identifies organ-specific tropisms of microbes, enrichments of anaerobic bacteria in hypoxic tumors, and associations between microbial diversity and tumor-infiltrating neutrophils. Notably, Fusobacterium abundance is associated with poor immunotherapy response in non-small cell lung cancer (NSCLC) patients. The study also reveals that immunotherapy can reshape the metastatic tumor microbiome, reducing bacterial diversity and affecting treatment outcomes. The findings highlight the potential of the tumor microbiome as a target for enhancing cancer therapy and provide a valuable resource for future research.