Anatomy Of The Large Bowel Cancer.

The large bowel, also referred to as the large intestine, is about three to four feet long, arching across the body from right to left. It begins at the cecum, the point at which the small intestine enters the colon, and ends at the anus. The last four inches are called the rectum; the remainder is the colon, which is divided into five parts: the cecum, ascending colon, transverse colon, descending colon, and sigmoid colon

 Most cancers of the large bowel occur on the left (or distal) side in the segment closest to the rectum.

About one of seven large bowel cancers can be reached when the physician performs a rectal examination with a finger inserted into the anus.

Therefore a digital rectal examination, along with simple chemical testing of a small stool sample for microscopic (occult) blood, should be part of a periodic or general physical examination. In fact the examination for occult blood is a simple, inexpensive test that can be performed at home by placing a small amount of stool on chemically treated paper and returning it by mail for laboratory analysis. Since most bowel cancers ooze small amounts of blood, the presence of blood in the stool indicates that further examinations should be performed to rule out cancer. It should be noted, however, that other conditions such as hemorrhoids also may result in blood in the stool, therefore a positive occult blood test does not necessarily mean cancer.

Causes Of Large Bowel Cancer.
Cancer of the large bowel occurs much more frequently in the United States, Western Europe, Australia, and New Zealand than in Japan, Africa, and most of the developing or third world countries. Furthermore, since most types of cancers increase in frequency as we grow older, the fact that the number of older people in the United States is growing would also explain the rise in the incidence of large bowel cancer. The number of deaths, however, has remained constant, indicating that the overall cure rate is improving. This improvement, for reasons that are unknown, seems to be confined to women.

Although the cause of large bowel cancer is not known, most epidemiologists (doctors who study the statistical patterns of disease) associate it with diet in particular, the low-fiber, high-protein, high-fat content that characterizes the diet of most Americans and people in other urban, industrialized societies. For example, when the Japanese, who have a very low incidence of large bowel cancer in their homeland, move to Hawaii and the continental United States and adopt the typical American diet, their descendants suffer the higher risk of large bowel cancer that is seen in the general American population.

It is not known exactly how diet leads to bowel cancer, but it is generally thought that it involves the digestion of fats. Bacteria that live in the channel (lumen) of the large bowel are thought to modify the fats we eat to form cancer-causing agents (carcinogens) that injure the surface of the large bowel and ultimately cause cancer in some people. Since it takes many years of exposure to the modified fats to produce cancer, many experts believe that reducing the contact of these carcinogens with the bowel tissue may help protect against the disease. In recent years the possible protective role of dietary fiber for example, roughage, such as bran and other substances that are not digested by humans against bowel cancer has gained considerable attention.

A number of researchers have proposed that dietary fiber acts to dilute the carcinogens formed by intestinal bacteria and thereby reduces their concentration or the intensity of their exposure to the cells on the inside of the large bowel. Studies comparing the incidence of large bowel cancer among people who consume a diet low in fats and protein and high in carbohydrate and fiber vegetarians and Seventh-Day Adventists, for example and those who eat the typical American diet show that the latter suffer a much higher rate. This has led to the recommendations that Americans should alter their diet to reduce total fat and protein consumption while increasing fiber and carbohydrate.

Most experts in the field of large bowel cancer now agree that this particular type of cancer develops from a small benign mass (an adenoma) that grows from the surface of the bowel into the lumen or bowel channel. The adenoma looks like a grape or a mulberry and may range in size from barely visible to a width of several inches. Cancer cells may form within this growth, and the larger the size of the adenoma, the greater the chance of cancer cells being present. Adenomas are only one of several types of growths or polyps of the large bowel