Symptoms

Colorectal cancer in its early stages usually doesn't cause any symptoms. Symptoms occur later, when the cancer may be more difficult to treat. The most common symptoms include:

• Pain in the belly.
• Blood in your stool or very dark stools.
• A change in your bowel habits (such as more frequent stools or a feeling that your bowels are not emptying completely).
• Constant tiredness (fatigue).
• In rare cases, unexplained weight loss.

Colon cancer may not cause symptoms you notice in the early stages. When there are symptoms, they may depend on where the cancer is in your colon.

• The cecum and ascending colon, the first and second parts of the colon, are on the right side of your abdomen. Cancer in this area may bleed, causing blood in the stool and symptoms of anemia, including fatigue and weakness. The amount of blood may be small and so well mixed with stool that your stool may look normal. Sometimes cancer in this area does not cause many symptoms.
• The transverse colon, the third part, goes across your body from right to left. Cancer here may cause abdominal cramps.
• The descending colon, the fourth part, and the S-shaped sigmoid colon, the fifth part, are on the left side of your abdomen and join the rectum. Cancer here may cause narrower stools and bright red blood in the stool. Sometimes this blood is mistakenly thought to come from hemorrhoids.

Having these symptoms does not mean you have cancer. A number of other medical problems could cause similar symptoms, including:

• Irritable bowel syndrome, a common digestive problem that causes periods of stomach pain, cramping or bloating, and diarrhea or constipation.
• Other growths (polyps) in the large intestine that are not cancer.
• Diverticulitis, a condition in which pouches form in the wall of the colon and become painful, swollen, or infected.
• Infections that cause diarrhea, such as salmonella.
• Inflammatory bowel disease, such as Crohn's disease and ulcerative colitis, which cause swelling and sores in the intestines.
• Bleeding hemorrhoids.
• Ulcers of the rectum.