The colon is another name for the large intestine. The colon is primarily responsible for absorbing water and compacting fecal matter, although it can also absorb certain nutrients (primarily vitamins). The colon is lined by cells called epithelial cells, which can develop genetic mutations that cause them to grow abnormally quickly. This can lead to colon cancer.
Local Signs
One of the earliest signs of colon cancer is bleeding from the rectum. Part of this is because the blood vessels in the colon are thin and are present near the surface. This means that any sort of unusual growth can expose these blood vessels to additional friction, causing them to rupture. The blood may appear in stool samples, but sometimes the bleeding is slight enough that it may not be obviously apparent. Instead, the blood in the stool may be diagnosed using a routine test called an fecal occult blood test, in which a physician smears a small amount of feces on a piece of paper with chemicals designed to react with blood. Because bleeding is such a common health sign for colon cancer, any example of bleeding from the colon or rectum may require a colonoscopy to look for the presence of colon cancer. Other health signs can be sudden weight loss and fatigue from the body trying to fight off the cancer.
Intestinal Blockage
Sometimes a colon tumor will not initially cause any bleeding, which can allow it to grow to a larger size. In this case, the colon cancer may cause intestinal blockage as one of its first health signs. Intestinal blockage can cause severe pain in the abdomen when food and fecal matter accumulate and back up against the blockage. It can also cause severe gas and indigestion that is sometimes accompanied by nausea and vomiting. Patients with an intestinal blockage will also be unable to pass fecal matter through. This can be a medical emergency and will often require surgery to correct the problem.
Advanced Health Signs
Sometimes colon cancer does not cause any symptoms for an extended period of time, which may allow the cancer to spread to other tissues (via a process known as metastasis) before it is detected. Signs of advanced colon cancer (as in cancer that has spread) can include swelling of the lymph nodes (either in the neck or under the arm). Colon cancer can also cause dysfunction in any organ to which it spreads, so patients may develop liver failure (marked by easy bleeding/bruising and jaundice), lung problems (such as a persistent cough or difficulty breathing) or severe pain in their bones.
