Within a tumour, cancer cells are surrounded by varying cell types including endothelial cells, fibroblasts and infiltrating immune cells. In addition to these, there is molecular evidence of an intratumoural microbiota in most major solid cancers. Imaging analysis of patient tumours suggest that bacterial members of the intratumoural microbiota can be located intracellularly in epithelial and immune cells. However, the precise identity of both the host cell types and the intracellular bacteria, along with the functional impact of these microbes on host cells, remained unknown.