In the 1980s, several Japanese researchers began to report that they could detect flat-type carcinoma with a diameter of less than 10 mm arising de novo, which tended to reach the deeper layers at an earlier stage than polypoid-type carcinoma in adenoma.[118–120] This flat-type carcinoma[121] shows fewer mutations of the APC and K-ras genes than polypoid-type carcinoma, although mutations of the p53 genes are seen at the same level as in polypoid-type carcinoma. This evidence concerns the gene KRAS and adenoma.