WHAT ARE COLON AND RECTAL CANCERS?

Colon and rectal cancer develop in the digestive tract, which is also called the gastrointestinal, or GI, tract. The digestive system processes food for energy and rids the body of solid waste matter (fecal matter or stool).

After food is chewed and swallowed, it travels through the esophagus to the stomach. There it is partly broken down and then sent to the small intestine, also known as the small bowel. The word "small" refers to diameter of the small intestine, which is narrower than that of the large bowel. But, the small intestine is actually the longest segment of the digestive system -- about 20 feet.

The small intestine continues breaking down the food and absorbs most of the nutrients. The liver and the pancreas release bile and enzymes into the small bowel to aid in this process. The small intestine joins the large intestine or large bowel, a muscular tube about five feet long. The first part of the large bowel, called the colon continues to absorb water and mineral nutrients from the food matter and serves as a storage place for waste matter. The waste matter left after this process goes into the rectum , the final 6 inches or so of the large bowel. From there it passes out of the body through the anus.

Each of these sections of the colon and rectum has several layers of tissue. Colorectal cancers start in the innermost layer and can grow through some or all of the other layers. Knowing a little about these layers is important, because the stage (extent of spread) of a colorectal cancer depends to a great degree on which of these layers it affects. For more information, refer to the section of this document on staging.

Colon cancer and rectal cancer have many features in common. Sometimes they are referred to together as colorectal cancer.

Colorectal cancers are thought to develop slowly over a period of several years. Before a true cancer develops, there usually are precancerous changes in the lining of the colon or rectum. These changes might be dysplasia or adenomatous polyps . A polyp is a growth of tissue into the center of the colon or rectum. Some types of polyps (hyperplastic polyps and inflammatory polyps) are not precancerous. But, having adenomatous polyps, also known as adenomas , does increase a person''s risk of developing cancer, especially if they are large or there are many polyps.

COLORECTAL CANCER STATISTICS

Colorectal cancer is the third most common cancer diagnosed in men and women in the United States.  A total of 135,000 new cases and 56,600 deaths are estimated to occur in 2001.

About 98,000 new cases of colon cancer with 48,000 deaths, and 37,200 new cases of rectal cancer with 8,600 deaths, will occur in 2001.

The distribution of colon and rectal cancer cases and deaths in men and women are shown below:

The death rate from colorectal cancer has been declining over the past 20 years.  This may be due to improving screening.

RISK FACTORS FOR COLORECTAL CANCER

Researchers have identified several risk factors that increase a person's chance of developing colorectal cancer.

family history of colorectal cancer:  

Relatives of colorectal cancer patients are also at increased risk for developing this disease. Some of these families may have a colorectal cancer syndrome such as familial adenomatous polyposis (FAP) or hereditary nonpolyposis colorectal cancer (HNPCC). Colorectal cancer may also seem to run in some families that do not have one of these syndromes. 

It is important to accurately identify people with these syndromes, because their doctors will recommend specific measures to prevent cancer or find it as early as possible -- when treatment is most successful. Some doctors recommend that all people with colorectal cancer have an evaluation of their family history of the disease. People with a family history suggesting a colorectal cancer syndrome may consider genetic counseling and, in some cases, genetic testing. Strang Cancer Prevention Center recommends screening test schedules for people with increased colorectal cancer risk that differ from those generally recommended for people at average risk.

Familial colorectal cancer syndromes:  

The following conditions make it more likely that a family member could develop cancer:

• Familial adenomatous polyposis (FAP) - a hereditary condition that greatly increases a person's risk of developing colorectal cancer. People with this syndrome typically develop hundreds of polyps in the colon and rectum. Without preventive surgery, cancer nearly always develops in one or more of these polyps between the ages of 30 and 50. 
• Gardner's syndrome  - results in polyps and colorectal cancers that develop at a young age. It can also cause benign, or non-cancerous, tumors of the skin, soft connective tissue and bones. 
• Hereditary nonpolyposis colon cancer (HNPCC)  - develops in people at a relatively young age without first having many polyps. Women with this condition also have an increased risk of developing cancer of the endometrium (lining of the upper part of the uterus).
• Being of Eastern European Jewish descent - recent research has found an inherited tendency to develop colorectal cancer among some Jews of Eastern European descent. Like people with FAP, Gardner's syndrome, and HNPCC, their increased risk is due to an inherited mutation (change in DNA). This DNA change occurs much more commonly than the three other colorectal cancer syndromes, and is present in about 6% of American Jews. Additional research is needed to determine the extent to which this change increases risk. So far, there appears to be a relatively small increase in risk, much less than that caused by FAP, Gardner's syndrome, or HNPCC.  

Personal history of colorectal cancer:  

Even when a colorectal cancer has been completely removed, new cancers may develop in other areas of the colon and rectum.

Personal history of intestinal polyps:  

Some types of polyps (hyperplastic polyps and inflammatory polyps) do not increase the risk of colorectal cancer. Other types, such as adenomatous polyps, do increase the risk of colorectal cancer, especially if they are large or numerous.

Personal history of chronic inflammatory bowel disease:  

Chronic inflammatory bowel disease (ulcerative colitis or Crohn's colitis) is a condition in which the colon is inflamed over a long period of time and may have ulcers in its lining. This increases a person's risk of developing colon cancer, so starting colonoscopy earlier and doing this test more often (every 1 to 2 years is recommended).

Aging:  

About 90% of people found to have colorectal cancer are 50 years of age or older.

A diet mostly from animal sources:  

A diet consisting mostly of foods that are high in fat, especially from animal sources, can increase the risk of colorectal cancer. Instead, Strang recommends choosing most of your foods from plant sources and limiting intake of high-fat foods, such as those from animal sources. Strang also recommends eating at least five servings of fruits and vegetables every day, and six servings of other foods from plant sources such as breads, cereals, grain products, rice, pasta, or beans. Many fruits and vegetables contain substances that interfere with the process of cancer formation.

Physical inactivity:  

People who do not get at least a moderate degree of physical activity have an increased risk of developing colorectal cancer.

Being very overweight increases a person's colorectal cancer risk. Having excess fat in the waist area increases this risk more than having the same amount of fat in the thighs or hips. Researchers suggest that the excess fat changes metabolism in a way that increases growth of cells in the colon and rectum, and that fat cells in the waist area have the largest impact on metabolism.