KRAS and cancer: The number of pigs genetically modified to replicate human diseases has increased dramatically.3 Valuable models such as cystic fibrosis and diabetes are established.4, 5 Work is also proceeding towards genetically defined porcine cancer models, such as inactivation of BRCA1 for breast cancer,6 mutation of TP537 and, as we have reported, knockout and conditional activation of mutant TP53,8 latent oncogenic KRAS mutation9 and truncating mutations of APC to model colorectal cancer.10 The relevance of pig cancer models depends on how closely they resemble human disease.