1.Early colorectal cancer. Cancer cells limited to the submucosal layer of the colorectum are called early colorectal cancer (pT1), and the WHO classification of gastrointestinal tumors also calls lesions with infiltration in the mucosal layer “high-grade intraepithelial neoplasia”. 2.The general types of progressive colorectal cancer. (1) Bulging type. Any tumor body protruding into the intestinal lumen belongs to this type. (2) Ulcerated type. Any tumor that forms an ulcer deep to or through the muscle layer is of this type. (3) Infiltrative type. The tumor infiltrates diffusely into all layers of intestinal wall, thickening the local intestinal wall, but there is often no obvious ulcer or bulge on the surface. 3. Histological types. (1) Adenocarcinoma: (1) Papillary adenocarcinoma; (2) Tubular adenocarcinoma; (3) Mucinous adenocarcinoma; (4) Indolent cell carcinoma; (2) Undifferentiated carcinoma; (3) Adenosquamous carcinoma; (4) Squamous cell carcinoma; (5) Small cell carcinoma; (6) Carcinoid tumor.