A substantial proportion (at least 15 per cent) of the global cancer burden is attributable to known infectious agents, such as HPV, HBV and H. pylori. It is possible that infectious agents may have a still greater role in cancer etiology, but traditional methods for finding them have limited sensitivity. The Holt lab find pathogens by their sequence signatures in human tissues using genomic methods. Their application of these methods to colorectal carcinoma identified a strong link to the emerging pathogen Fusobacterium nucleatum (Castellarin et al., Genome Research 2011). Currently, as part of the Cancer Research UK OPTIMISTICC Grand Challenge program, the group is characterizing the host immune response to F. nucleatum and other oncomicrobes, to inform vaccine development.