I. Colorectal cancer has a certain degree of heredity Research shows that if a patient with colorectal cancer is found in a certain family, the probability of colorectal cancer occurring in blood relatives (parents, children, brothers and sisters) with him is significantly higher. The occurrence of colorectal cancer is closely related to diet and environment The people of the same family, on the one hand, have similar genetic background; on the other hand, they live together for a long time and have common eating habits. So having the same risk factors, the risk of developing colon cancer is 2-3 times higher than the normal population. Early colonoscopy is recommended for the following people According to the U.S. colorectal cancer diagnosis and treatment standard, colonoscopy is recommended for normal people over 50 years old and relatives of colorectal cancer aged 40-45 with the following symptoms 1. long-term positive fecal occult blood (fecal routine + positive occult blood test); 2. change in bowel habit: frequent diarrhea or constipation recently, change in stool shape or thinning compared with before; 3. mucus and blood stool: bright red or dark red blood or mucus is often found in stool; 4. long-term anemia and fatigue, unexplained sudden weight loss.