It demonstrates two main reasons for the suitability of feline intestinal tumors as a valid spontaneous in vivo model for late-stage human CRC: (1) Feline intestinal carcinomas resemble human subtypes and present with an invasive growth and high tumor budding activity, (2) CTNNB1 mutations are present in feline intestinal carcinomas, as has been reported in human and canine intestinal tumorigenesis. The gene discussed is CTNNB1; the disease is colorectal carcinoma.