In outpatient clinics, we often encounter patients with blood in stool who come to the clinic with anxiety, and a very important reason is that they are worried that they are suffering from bowel cancer. In fact, most patients with blood in stool are not suffering from bowel cancer, so what are the characteristics of blood in stool of bowel cancer? First of all, let’s have a general introduction about bowel cancer. Usually, we refer to colon cancer, while small intestine cancer is relatively rare (accounting for only about 2% of gastrointestinal malignant tumors). The human large intestine includes: cecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon and rectum. Depending on the anatomical location, embryogenesis, genetic characteristics, clinical manifestations and treatment modalities, colorectal cancer is medically classified into: right hemicolectomy, left hemicolectomy and rectal cancer. The right hemicolectomy includes: cecum, ascending colon and proximal 2/3 of transverse colon; the left hemicolectomy includes: distal 1/3 of transverse colon, descending colon and sigmoid colon; the rectum is the intestinal tube within about 15 cm from the anal verge. Blood in stool is the most common clinical manifestation of bowel cancer, but the manifestation of blood in stool is not the same in different parts of bowel cancer. Rectal cancer and left colon cancer: mucus dark red blood stool In general, the closer the location of intestinal tumor is to the anus, the fresher the color of blood in stool, the easier it is to be detected by patients. The bleeding of bowel cancer is usually the chronic rupture and bleeding of the tumor in the intestinal cavity, and the blood will be mixed with the stool, which is dark red, and the ruptured surface of the tumor will also be secondary to infection, resulting in more inflammatory exudate and mucus, so the characteristics of the blood in the stool of rectal cancer and left semi-colon cancer are: mucus dark red blood in the stool and mixed blood in the stool. The blood in the stool of rectal cancer that is closer to the anus will be more red in color, and the blood in the stool of left hemicolectomy will be slightly darker. How is this different from bleeding from hemorrhoids again? Simply speaking, the formation of hemorrhoids is due to the varicose blood vessels in the anus. Since the hemorrhoid vascular mass is very close to the anus, it will manifest when the patient holds his breath and exerts himself before the stool, the anal sphincter will contract and squeeze the vascular mass to rupture, resulting in blood dripping or even spraying; after the stool, the anal sphincter reflexively contracts and blood drips again, and the blood is discharged in steps with the stool, so hemorrhoid bleeding is characterized by blood dripping or spraying and blood separating from the stool. In fact, bowel cancer usually does not only manifest as blood in stool, but also often accompanied by some other symptoms: rectal cancer also includes change in stool habit, more frequent stools, urgency, thin stools, etc.; left hemicolectomy cancer is also accompanied by abdominal pain, abdominal distension, poor bowel movement, etc. 2.Right hemicolectomy cancer: no blood visible to the naked eye, positive fecal occult blood test Right hemicolectomy cancer is far from the anus, and the chronic bleeding of tumor is small and mixed with a large amount of stool, so it is not easy for patients to find stool abnormalities, but fecal occult blood test will be positive. Therefore, right hemicolectomy cancer, usually does not come to the hospital with blood as a sign, but is detected due to unexplained anemia, right lower abdominal pain, abdominal mass, wasting, and positive fecal occult blood on physical examination test and undergoes further examination in the hospital. In addition, it is important to be alert that right lower abdominal pain should not be easily taken as appendicitis. The appendix is located at the beginning of the right hemicolectomy, and when the appendix tumor grows to a certain size, it will show as right lower abdominal pain, and this symptom exists chronically, so it is easy to be mistaken as chronic appendicitis without paying attention to it. Therefore, for middle-aged and elderly patients with right lower abdominal pain, especially those with family history of tumor or history of other tumors, accompanied by weakness or anemia, they need to be alert to the possibility of right hemicolectomy, and they need to go to the hospital in time to receive abdominal CT and colonoscopy. As seen above, blood in stool does not necessarily mean intestinal cancer, but there are characteristics of blood in stool of intestinal cancer, and there are differences in the manifestations of blood in stool of different parts of intestinal cancer. Scientific understanding of blood in stool can reduce unnecessary tension, and at the same time, we should pay attention to blood in stool, and promptly seek medical consultation when it has the above clinical manifestations, especially for those patients who have a history of colon or rectal cancer, a history of intestinal polyp, adenoma or cancer, persistent positive fecal occult blood or high tumor markers such as CEA.