There is a widely known relationship between certain microbes and cancer progression. For instance, is associated with the occurrence of gastric cancer, while HPV is associated with cervical and head and neck cancers. Recent studies have uncovered novel and important associations between bacterial presence and tumor formation and treatment response. Apart from the influence of the intestinal microbiome on cancer, the local activity of bacteria affects disease properties as well. Bacteria can localize within tumors in less vascularized niches. Their presence mediates the activity of signaling pathways, which contribute to tumorigenesis. Furthermore, they affect the composition of the tumor microenvironment, a highly complex structure composed of immunoregulatory cells and secreted inflammatory mediators. Recently, researchers have analyzed the properties of bacteria to develop novel anticancer strategies. The aim of this review is to discuss the latest findings regarding the relationships between bacteria and cancer and the properties of bacteria that could be used to kill cancer cells.