The rare cecal adenomas arising in CDX2P-CreERT2Apcfl/flCtnnb1fl/+ mice were found to have significant fractions of cells that escaped Cre-mediated Ctnnb1 targeting, even though Cre-mediated somatic inactivation of both Apc alleles occurred to the same extent in the rare adenomas and proximal colon mucosa (S1 Fig). The gene discussed is APC; the disease is adenoma.