When a tumor occurs in the colon, a mass may appear in the lower part of the abdomen, which is hard under the belly button and painful when pressed. It is necessary to go to hospital for examination in time to understand the location, size, boundary and mobility of the mass, and abdominal CT and colonoscopy are needed. CT abdomen can reveal the location of the mass and whether there are enlarged lymph nodes around the mesentery; colonoscopy can visually reveal the location of the mass and the lesion of the mass, and a small amount of tissue can be taken out for laboratory tests. If the diagnosis of colon cancer is confirmed by pathological examination, surgery is usually required.