ARID1A and cancer: In MX1-Cre;Arid1afl/fl mice, where both Arid1a alleles are inactivated across many tissues, nodular and polypoid tumors in the colons are obtained at multiple non-contiguous sites but never in the small intestine, whose histology is consistent with invasive colon adenocarcinoma, a malignant neoplasm derived from glandular colonic epithelium.