Early stage of colorectal cancer is asymptomatic, or the symptoms are not obvious, only discomfort, indigestion, fecal occult blood, etc. With the development of colorectal cancer, symptoms gradually appear. With the development of cancer, symptoms gradually appear, manifesting as change of bowel habit, abdominal pain, blood in stool, abdominal mass, intestinal obstruction, etc., with or without systemic symptoms such as anemia, fever and emaciation. Metastasis and infiltration of the tumor may cause changes in the affected organs. Colorectal cancer shows different clinical symptoms and signs according to different parts of the body. The main clinical symptoms of right half colon cancer are loss of appetite, nausea, vomiting, anemia, fatigue and abdominal pain. Right half colon cancer leads to iron deficiency anemia, which manifests fatigue, weakness, shortness of breath and other symptoms. Due to the wide lumen of right half colon, the tumor grows to a certain volume before abdominal symptoms appear, which is also one of the main reasons for late staging when the tumor is diagnosed. Left half colon cancer: The lumen of left half colon is narrower than that of right half colon, and left half colon cancer 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, abdominal distension and so on. Stools with fresh bleeding indicate that the tumor is located in the end of the left half of the colon or in the rectum. The diagnosis of the stage of the disease is often earlier than that of right half colon 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, it is easy to bleed by friction of fecal mass, which is mostly bright red or dark red, not mixed with formed feces or attached to the surface of fecal column, which is misdiagnosed as hemorrhoidal bleeding. Stimulation of the lesion and secondary infection of ulceration of the mass, which constantly causes defecation reflex, can easily be misdiagnosed as “enteritis” or “bacillary dysentery”. If the cancer grows in ring shape, it will lead to narrowing of intestinal lumen, which will manifest as deformation and thinning of fecal column in early stage and incomplete obstruction in 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, causing corresponding clinical symptoms. Anal incontinence, persistent pain in lower abdomen and lumbosacral region are caused by rectal cancer invading into sacral plexus. Tumor cells planted and metastasized to the abdominopelvic cavity, forming corresponding symptoms and signs. Rectal fingerprinting can find lumps in the vesicorectal fossa or uterorectal fossa, and the tumor is widely planted and metastasized in the abdominopelvic cavity, forming abdominal effusion. 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 can also metastasize to liver, lungs, bones and other parts of the body through bloodstream.