Characterization of the tumor microbiome of brain metastases and glioblastoma reveals tumor-type-specific and location-specific microbial signatures

Brain tumors, including glioblastoma multiforme (GBM) and brain metastases, present a notable clinical challenge. Recent research highlights the presence of intratumor bacteria across many tumor types, yet the microbiome of brain tumors remains largely underexplored. Here we show that the microbiome of 322 brain tumors differs markedly by tumor type and location. Using multiple approaches to visualize, culture and sequence bacterial communities, we found that brain metastases harbor higher bacterial richness and diversity than GBM, with distinct microbial compositions. Moreover, metastases in posterior brain regions exhibited greater diversity than those in anterior regions. Pathway analysis revealed enrichment of bacterial metabolic pathways associated with tumor spread and metastasis in brain metastases while GBM was enriched with pathways supporting alternative phosphorus use. These findings provide valuable insights into the microbial landscape of brain tumors, highlighting tumor-type-specific and location-specific variation and suggesting potential roles for bacteria in brain tumor biology.