What is Colorectal Cancer?

A cancer originating in the colon, or rectum, makes up this group. The colon and rectum are continuous, but the differing treatments for cancers arising in different parts of the intestinal tract makes it useful to distinguish them by location. The colon is also known as the "large intestine," and starts where the small intestine ends, in the area of the lower right portion of the abdomen. The area where the small intestine becomes the colon is called the"cecum," and the fingerlike "appendix" is located nearby. The colon is shaped like an arch. The right leg of the arch is called the "ascending colon," and runs up the right side of the abdomen, bending under the liver. The arching portion is the "transverse colon," and it runs under the pancreas and stomach, ending under the spleen. The left portion of the arch is the "descending colon" running down the left side of the abdomen. The descending colon connects to the "sigmoid colon," which is shaped like an "S," and moves toward the center of the pelvis. The sigmoid colon joins the "rectum" at the "recto-sigmoid" junction; the rectum is about 7 inches long. The rectum becomes the"anal canal" at the "ano-rectal" junction, this canal is about 2 inches long and terminates as the "anus," where bowel movements actually leave the body. Since the lining cells inside the colon and rectum are similar, and produce mucous, the cancers that arise in this part of the digestive system are also similar, and considered together. However, the cells lining the inside of the anal canal are different, so different cancers arise there, and this is a separate topic.

The colo-rectum has a rich blood supply ; this is needed to absorb nutrients from the bowel and get them into the bloodstream. The "mesenteric" arteries arteries are large branches off of the body's main artery (the "aorta"), and provide fresh blood with oxygen and nutrients to the bowel. If that blood supply is cut off, the bowel will become "infarcted" (shut off from fresh blood), painful, and ultimately die ("necrosis"). This will allow the bacteria normally within the bowel, which solidify stool, to escape into the sterile abdomen causing infection ("peritonitis"). The bowel can become infarcted from a blood clot in the mesenteric blood vessels, becoming twisted upon itself ("torsion"), telescoping in upon itself ("volvulus"), or by a growing tumor. Blood is drained from the bowel by the "mesenteric" veins, which send that blood through the liver ("portal vein") to extract and process digested fats, proteins and sugars. The processed blood is then returned to the heart by the large vein draining the liver ("inferior vena cava"). The point is that infection or cancer cells can travel from the bowel up into the liver, and from there through the regular bloodstream to other areas . If a cancer spreads ("metastasizes") via the bloodstream, it is called "hematogenous metastasis." Initially, single cancer cells traveling in the bloodstream will "seed" other areas ("micrometastasis"), and eventually (if unchecked) grow into large tumors there.

The bowel also has within it a series of "patches" of clumps of White Blood Cells, called "Peyer's Patches." These are called "lymphoid tissue," much like the tonsils in the throat, and help fight infection in the bowel. The bowel has an inner lining of specialized cells (see below) called the "mucosa," but it's walls are made of "muscle layers." These muscle layers allow the bowel to move ("peristalsis") so digesting food is passed through. Just underneath the delicate mucosal inner lining, but before the muscle layers, is an area of loose connective tissue called the "submucosa." Within the submucosa exists a network of "lymph channels," which collect the "tissue fluid" that has migrated out from the blood vessels, to bathe and nourish each cell. These lymph channels drain to pea-sized "lymph nodes" around the bowel, which are filled with White Blood Cells. The purpose of the lymph nodes is to filter and purify the blood, trapping germs and cancer cells. When lymph nodes are invaded by infection or cancer, they swell ("lymphadenopathy") . Normal "lymph fluid" is eventually returned back into the blood stream, after purification by the lymph nodes. The importance of this is that the lymph system can act as a conduit for spread of infections or cancer ("lymphogenous metastasis"). Commonly, but not always, the local lymph nodes are involved before more distant sites.

What is Colo-Rectal Cancer?

The cells lining the inner colon and rectum are called "columnar epithelial cells," and also "goblet cells" which secrete mucous to help keep the stool soft. These cells invaginate (fold upon themselves) to form glands, and the type of cancer which most commonly arises from glands is called "adenocarcinoma." As with all cells in the body, the production of new cells lining the intestine is under tight control from the "genes" within each cell, which are themselves composed of the basic genetic material "DNA." In the growing child, the cells divide quickly to form the enlarging intestines, but in the adult cells are only produced to replace those that die of injury or lost to old age. Colon cancer, like any cancer, starts in a single cell . This cell loses control of it's division and then starts to reproduce in a haphazard, uncontrolled manner to form a "tumor." A tumor merely means a swelling, it can be caused by most anything and is not necessarily cancer. A "benign" tumor, also called a "polyp" within the intestines, only grows within it's local area; it cannot go to other areas of the body and so is not cancer. In contrast, a "malignant" tumor is capable of spreading to any area of the body, it is cancer. This process of spread is called "metastasis." Sometimes previously benign tumors can become malignant over time, this process is called "malignant degeneration" and happens in some polyps. Most polyps, however, will never become cancerous. If cancer does arise and is not effectively treated, the will ultimately spread to other crucial body areas and kill the patient. Advanced colon cancer most often kills by causing anemia, debility, infection, and organ failure. This is why it is critical to diagnose and treat any cancer as early as possible, when the chances for successful treatment are highest.