Coley demonstrated some 140 years ago that the course of cancer could sometimes be favourably altered by activating the host immune system with bacterial toxins. Today my lab’s work is focused on testing a hypothesis that some cancers can paradoxically be promoted by bacterial toxins produced by our resident microbiome. My lecture will focus on our current understanding of the role of innate and adaptive immunity in cancer induction and cancer treatment, and the prospects for specific immunological interventions to reduce the risk of future cancer.