The classification of rectal cancer is based on the general morphology of the tumor: the first one is the bulging type, which is growing into the lumen of the tube, and this one has a better prognosis. The second one is ulcerated type, that is, the wall of the tube is ulcerated, this kind of prognosis is worse. The third is the infiltrative type, which grows into the wall of the duct, and the duct wall becomes hard and thick, and this kind of prognosis is also very poor. According to the histocytology, the first type is adenocarcinoma, the second is mucinous carcinoma, the third is undifferentiated carcinoma, and the fourth is the rare squamous cell carcinoma and adenosquamous carcinoma.