The main symptoms of rectal cancer are rectal irritation such as: change of stool habit (constipation or diarrhea or both), change of stool characteristics (such as thin stool, bloody stool, mucus stool, etc.), urgency and heaviness (feeling of incomplete stool), lower abdominal pain or abdominal discomfort, and abdominal mass. In some patients, the first onset of tumor has already caused intestinal obstruction: manifested as abdominal pain and distension, unable to ventilate and defecate. In some patients, the tumor has already invaded adjacent organs at the time of consultation, such as urinary frequency and urgency, pus and hematuria, or coming out of the anus during urination (invasion of the vesicoureter, etc.), and in female patients, there is vaginal mid-bowel exit (rectovaginal fistula), while individual patients even have severe sacrococcygeal pain (invasion of nerves). It is important to note that some patients with rectal cancer may not have any symptoms and may be detected by accidental physical examination or during abdominal examination for other diseases. Most of the outpatients visit the clinic for blood in the stool, and most of them mistakenly think they have “hemorrhoids”.