Colorectal cancer is a common malignant tumor, including colon cancer and rectal cancer. The incidence of colorectal cancer is from high to low: rectum, sigmoid colon, cecum, ascending colon, descending colon and transverse colon, and in recent years there is a tendency to develop to the proximal end (right hemicolectum). Its incidence is closely related to lifestyle, genetics and colorectal adenoma. The age of incidence tends to be older, and the ratio of men to women is 1.65:1. Clinical manifestations of colorectal cancer are asymptomatic in early stage, or the symptoms are not obvious, such as discomfort, indigestion and occult blood in stool. With the development of cancer, symptoms will gradually appear, including change of stool habit, abdominal pain, blood in stool, abdominal mass, intestinal obstruction, etc., with or without systemic symptoms such as anemia, fever and emaciation. Tumor may cause changes in affected organs due to metastasis and infiltration. Colorectal cancer shows different clinical symptoms and signs due to different sites. 1. Right hemicolectomy The main clinical symptoms of right hemicolectomy are loss of appetite, nausea, vomiting, anemia, fatigue and abdominal pain. Right hemicolectomy causes iron-deficiency anemia, which shows fatigue, weakness and shortness of breath. Because of the wide intestinal cavity, abdominal symptoms will only appear when the tumor grows to a certain volume in the right hemicolectomy, which is one of the main reasons for the late stage when the tumor is diagnosed. Left hemicolectomy The left hemicolectomy lumen is narrower than the right hemicolectomy lumen, so left hemicolectomy is more likely to cause complete or partial intestinal obstruction. Bowel obstruction leads to change of stool habit, constipation, blood in stool, diarrhea, abdominal pain, abdominal cramps and bloating. Fresh bleeding stools indicate that the tumor is located in the left hemicolectomy or rectum. The diagnosis of the disease stage is often earlier than that of right hemicolectomy. Rectal cancer The main clinical symptoms of rectal cancer are blood in stool, change of bowel habit and obstruction. If the cancer site is low and the fecal mass is hard, the bleeding is easily caused by the friction of the fecal mass, which is mostly bright red or dark red, not mixed with formed feces or attached to the surface of the fecal column, and misdiagnosed as “hemorrhoid” bleeding. The secondary infection caused by lesion stimulation and mass ulceration constantly causes defecation reflex, which is easily misdiagnosed as “enteritis” or “bacillary dysentery”. If the cancer grows in a circular pattern, it causes narrowing of the intestinal lumen, which is manifested as deformation and thinning of the fecal column in the early stage and incomplete obstruction in the late stage. 4. Tumor infiltration and metastasis The most common form of infiltration of colorectal cancer is local invasion, in which the tumor invades the surrounding tissues or organs, resulting in corresponding clinical symptoms. Anal incontinence, persistent pain in lower abdomen and lumbosacral region are caused by rectal cancer invading sacral plexus. Tumor cell implantation and metastasis to the abdominopelvic cavity will form corresponding symptoms and signs. Rectal finger examination can reveal masses in the cysto-rectal fossa or utero-rectal fossa, and tumor implantation and metastasis in the abdominopelvic cavity extensively will form peritoneal fluid. There are two main ways of distant metastasis of colorectal cancer: lymphatic metastasis and hematogenous metastasis. Tumor cells metastasize to lymph nodes through lymphatic vessels, and also to liver, lung, bone and other parts through bloodstream metastasis.