Why do some neoplasms form in certain sites and not in others? For example, serrated polyps develop only in the caecum of transgenic mice that express heparin-binding EGF-like growth factor (HB-EGF) throughout the intestine, indicating that non-genetic factors may be involved. Bongers et al. showed that alteration of the intestinal microbiome, such as through treatment with antibiotics, inhibited serrated polyp formation in the caecum. Although the offending microbial factors were not identified, the authors found that the development of serrated polyps was associated with reduced epithelial barrier function, bacterial invasion and inflammation. In particular, neutrophil depletion significantly reduced serrated polyp formation.