Colorectal cancer refers to cancerous tumors occurring in the cecum, ascending colon, transverse colon, descending colon, sigmoid colon and rectum, and is one of the most common malignant tumors, ranking third among all kinds of malignant tumors. In recent years, the incidence of colorectal cancer in China has been on the rise significantly, and the incidence rate in Shanghai alone has increased 2-3 times in 20 years. Especially, it is worth noting that the proportion of young people suffering from colorectal cancer is increasing. Although doctors are convinced that the increase in colorectal cancer is related to the increased fat content in the diet, however, its exact cause is still unclear. What is known to the medical community is that certain diseases are closely related to colorectal cancer, and people who suffer from these diseases are known as a high-risk group for colorectal cancer. Therefore, it is beneficial to understand these diseases and susceptible groups from the perspective of prevention and early diagnosis. Colorectal polyp: Polyp is a kind of superfluous organism growing out from the intestinal mucosa, which varies in size, shape, number and location. There are more middle-aged and elderly patients over 40 years old, and polyps are increasing with age, and the disease can be diagnosed by colonoscopy. The origin of polyps is divided into two main categories: adenomatous and hyperplastic (inflammatory). Adenomatous polyps are known to have a higher risk of cancer, especially multiple adenomatous polyps larger than 1 cm in diameter, which are known as precancerous lesions of the colon and must be removed; even if adenomatous polyps have been eradicated, they should be reviewed regularly to see if they recur. Ulcerative colitis: It is not colitis in general, but colitis with recurrent episodes of pus and blood in the stool as the main symptom and “mouth sore”-like ulcers visible on colonoscopy. The chance of cancer in ulcerative colitis is 5 to 10 times higher than in normal people, especially in people who develop the disease when they are underage and whose lesions have been active, extensive and have been in progress for more than 5 years, the risk of cancer is greater. It is worth noting that in recent years, there has been a significant increase in the number of patients with ulcerative colitis in China, and the number of patients with cancer caused by this is also increasing. Schistosomiasis japonica: The disease is endemic in the southern part of China south of the Yangtze River. The eggs of schistosomes exist in the mucosa of the large intestine for a long time to stimulate the intestinal mucosa and cause cancer. The detection rate of colorectal cancer is 12.3 times higher in areas heavily affected by schistosomiasis compared to areas without this disease. Those who have received radiation therapy to the pelvis: Patients with uterine and ovarian cancer often have to receive radiotherapy, and their incidence of rectal cancer is 4 times higher than normal, especially after 10 years of radiotherapy and with higher doses of radiotherapy. Those who have previously suffered from colorectal cancer: about 2% to 11% of colorectal cancer patients have a second primary colorectal cancer lesion (not recurrence) after the first one has been treated, which is called heterochronous multiple occurrence. Therefore, patients should not rest on their laurels just because they have been treated, but should be reviewed regularly. People who have previously undergone surgery for ovarian cancer or breast cancer, or had ureterosigmoid anastomosis are also at high risk of colorectal cancer. Family members of colorectal cancer patients: The incidence of colorectal cancer is three times higher in those with family history of colorectal cancer than those without family history, which may be related to the same dietary habits in addition to genetic factors. Others: Patients after cholecystectomy, patients after small bowel anastomosis, workers in asbestos processing industry and textile industry are also high-risk groups.