Symptoms of rectal cancer include changes in bowel habits, such as a feeling of heaviness around the anus, a constant need to defecate, or diarrhea. Some patients may experience constipation, or alternating episodes of diarrhea and constipation. Another common symptom is a change in the shape of the stool, with the stool becoming narrower. Additionally, abdominal pain and rectal bleeding are also common symptoms. Some patients with rectal cancer may exhibit clinical signs of intestinal obstruction, which includes constipation, inability to pass stool or gas, which means no flatulence. This is accompanied by nausea and vomiting. Other common symptoms include significant abdominal pain and bloating.