A condition involving chronic inflammation of the colon, called ulcerative colitis, is associated with an increased risk of developing colorectal cancer1. Moreover, this risk correlates with the cumulative effect of inflammatory episodes rather than the extent of active inflammation at the time of diagnosis2. Writing in Nature, Nagaraja et al.3 reveal that chronic colonic inflammation results in changes (called epigenetic modifications) that poise stem cells to form tumours if cancer-promoting genetic alterations subsequently occur. Access Nature and 54 other Nature Portfolio journals Get Nature+, our best-value online-access subscription $32.99 / 30 days cancel any time Subscribe to this journal Receive 51 print issues and online access $199.00 per year only $3.90 per issue Rent or buy this article Prices vary by article type from$1.95 to$39.95 Prices may be subject to local taxes which are calculated during checkout doi: https://doi.org/10.1038/d41586-026-00639-0 Ekbom, A., Helmick, C., Zack, M.…