By being alert to the symptoms of colorectal cancer, it may be possible to detect the disease early, when it is most likely to be treated successfully. Many people with colorectal cancer do not have any symptoms until the disease is advanced, so people need to be screened regularly.

People with colorectal cancer may experience the following symptoms. Sometimes, people with colorectal cancer do not show any of these symptoms. Or, these symptoms may be caused by a medical condition that is not cancer. If you are concerned about a symptom on this list, please talk with your doctor and ask that a colonoscopy be scheduled so that the underlying reason(s) for the symptom can be found.

• A change in bowel habits
  
   
• Diarrhea, constipation, or feeling that the bowel does not empty completely
  
   
• Bright red or very dark blood in the stool
  
   
• Stools that look narrower or thinner than normal
  
   
• Discomfort in the abdomen, including frequent gas pains, bloating, fullness, and cramps
  
   
• Weight loss with no known explanation
  
   
• Constant tiredness or fatigue
  
   
• Unexplained iron-deficiency anemia (low number of red blood cells)