For patients, they need to be alert to some adverse signs in the body in order to achieve early diagnosis and treatment. Usually, patients should pay attention to some uncomfortable symptoms of the digestive system, especially those recurrent or chronic diseases, which are medically known as precancerous lesions. Precancerous lesions of gastric cancer include: 1. chronic atrophic gastritis 2. gastric polyps 3. residual gastritis 4. pernicious anemia with significant atrophy of gastric body 5. few gastric ulcers; precancerous lesions of colorectal cancer include: 1. chronic ulcerative colitis 2. colorectal adenoma. The early symptoms of gastric cancer are not very obvious, so many people tend to confuse the symptoms of gastric cancer with those of gastric ulcer, so how to correctly distinguish these two diseases which are completely different in nature but often have many similarities in clinical manifestations, especially “ulcerated gastric cancer”? In order not to miss the disease, not only doctors should master the skills of distinguishing the two, but also patients should know some relevant knowledge in order to be alert and try to achieve early detection and early treatment of cancer. It is still possible to distinguish gastric ulcer from gastric cancer. Age and course of disease gastric ulcer is mostly seen in young adults, and 90% of patients have epigastric pain, which is cyclic in nature and can last for a few days, weeks or even months, and then relieved for a certain period of time, and then reoccurs again, often for many years. In contrast, gastric cancer is mostly found in middle-aged and elderly people over 40 years old. Early gastric cancer usually has no obvious discomfort, but once symptoms such as upper abdominal pain appear, it will be progressively aggravated, and the disease develops faster and has a shorter course. In terms of the regularity of pain, the pain of gastric ulcer is mostly closely related to diet, i.e. it starts half an hour after meal and lasts for several hours with a burning sensation, and then gradually disappears until the above rhythm is found again after the next meal, and the pain can be relieved by taking alkaline drugs. The pain of gastric cancer is irregular and not related to eating, and it can be aggravated or relieved after eating; the nature of pain is variable, it can be dull pain or severe pain, often with the feeling of fullness and distension. The early symptoms of colorectal cancer may include abdominal distension, discomfort and dyspepsia, followed by changes in bowel habits and blood in stool, mostly manifesting as more frequent bowel movements, unformed stool, mild abdominal pain before bowel movement, and later mucus stool or mucous-purulent blood stool. It is worth noting that some benign diseases such as hemorrhoids, anal fissures, intestinal polyps, dysentery, colitis, gastric ulcers, etc. often appear with blood in the stool and are easily confused with colorectal cancer, according to statistics, there are few patients with rectal cancer who are misdiagnosed as hemorrhoids in the early stage. The patient with colorectal cancer will have abdominal distension and pain due to intestinal obstruction, and when the cancer ruptures, the stool will have pus and blood, and the stool and blood will be mixed. However, in patients with hemorrhoids, anal fissures, and intestinal polyps, the stool does not mix with blood, but adheres to the surface of the stool, and the blood is bright red or relatively fresh. The stools of patients with gastric ulcers differ significantly from those of patients with enteritis, often passing black or tarry stools. In addition to the difference in stools, the accompanying symptoms are also different. Colorectal cancer patients have mucus and thick blood stools, while their bowel habits may change, sometimes with diarrhea and sometimes with constipation. This is because the growth of the cancer affects the normal physiological function of the intestinal canal, resulting in spasm at one time and contraction at another. In contrast, patients with hemorrhoids have protrusions visible in the anus during defecation, which are medically known as prolapsed hemorrhoids. Patients with anal fissures often have significant pain and a burning sensation in the anus during defecation. Patients with intestinal polyps do not have abdominal pain. Patients with dysentery may have fever, abdominal pain and urgency, i.e., the urge to go to the toilet but always feel that they can not finish pooping. Patients with ulcers have chronic, periodic pain in the upper abdomen and frequent belching, acid reflux, nausea and vomiting.