Most cancers in their early, most treatable stages don't cause any symptoms. That is why it is important to have regular tests to check for cancer even when you might not notice anything wrong. Common Signs and Symptoms When colorectal cancer first develops, there may be no symptoms at all. But as the cancer grows, it can cause changes that people should watch for. Common signs and symptoms of colorectal cancer include: - a change in the frequency of bowel movements  - diarrhea, constipation, or feeling that the bowel does not empty completely  - either bright red or very dark blood in the stool  - stools that are narrower than usual  - general abdominal discomfort such as frequent gas pains, bloating, fullness, and/or cramps  - weight loss with no known reason  - constant tiredness  - vomiting a change in the frequency of bowel movements diarrhea, constipation, or feeling that the bowel does not empty completely either bright red or very dark blood in the stool stools that are narrower than usual general abdominal discomfort such as frequent gas pains, bloating, fullness, and/or cramps weight loss with no known reason constant tiredness vomiting These symptoms may be caused by colorectal cancer or by other conditions. It is important to check with a doctor if you have symptoms because only a doctor can make a diagnosis. Don't wait to feel pain. Early cancer usually doesn't cause pain. Lowering Your Risk Factors Lower your risk factors where possible. Colon cancer can be prevented if polyps that lead to the cancer are detected and removed. If colon cancer is found in its earliest stages, it is up to 90 percent curable. Tools for Early Detection Beginning at age 50, the following tools are all used for early detection. They can help identify pre-cancerous conditions. If you are younger than 50 and one of your first-degree relatives has had colon cancer, you should consult with your doctor. Tools used for early detection: - A fecal occult blood test, or FOBT, is a test used to check for hidden blood in the stool. Sometimes cancers or polyps can bleed, and FOBT can detect small amounts of bleeding. Newer, genetically-based stool tests are proving to be more accurate than older tests.  - A sigmoidoscopy is an examination of the rectum and lower colon -- or sigmoid colon -- using a lighted instrument called a sigmoidoscope.   - A colonoscopy is an examination of the rectum and the large intestine (but not the small intestine) using a lighted instrument called a colonoscope.   - A virtual colonoscopy, which requires the same preparation as a standard colonoscopy, is done with an external scanning machine as opposed to a device inserted into the colon, although the colon does need to be inflated with gas for proper scanning. A fecal occult blood test, or FOBT, is a test used to check for hidden blood in the stool. Sometimes cancers or polyps can bleed, and FOBT can detect small amounts of bleeding. Newer, genetically-based stool tests are proving to be more accurate than older tests. A sigmoidoscopy is an examination of the rectum and lower colon -- or sigmoid colon -- using a lighted instrument called a sigmoidoscope. A colonoscopy is an examination of the rectum and the large intestine (but not the small intestine) using a lighted instrument called a colonoscope. A virtual colonoscopy, which requires the same preparation as a standard colonoscopy, is done with an external scanning machine as opposed to a device inserted into the colon, although the colon does need to be inflated with gas for proper scanning.