The uses of screening are as follows: 1) Early detection of tumors and early treatment can improve the cure rate of tumors, and the earlier the tumors are detected, the more chances of surgical resection, and the greater the possibility of cure. 2) Many precancerous lesions will be detected through screening, and it is possible to detect the cancerous changes in the early stage of the regular examination of these precancerous lesions, and some of the precancerous lesions even need to be dealt with in time to reduce the incidence of cancer, which not only reduces the cost, but also significantly improves the survival time of patients. For example, most of colorectal cancers are evolved from adenomas, so timely removal of these adenomas after timely detection through colonoscopy can greatly reduce the incidence of colorectal cancer.