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Colon Cancer; Overview.

Only lung cancer kills more Americans than colorectal cancer. Fear, denial and embarrassment keep many people from being screened for the disease. There is also a misperception that colon cancer mainly strikes men. Yet colorectal cancer is the third most common malignancy in women after breast and lung cancer. Men and women develop colorectal cancer with almost equal frequency. In fact, more women over 75 die of colorectal cancer than of breast cancer.

There are regional differences in the disease's incidence and mortality throughout the country with the highest rates occurring among those in the Northeast, and survival rates lowest among African Americans.

The good news is that the disease is not only highly beatable and treatable, but also highly preventable. Screening for colon cancer can reduce deaths from colon cancer by at least 60 percent by preventing its development in the first place. .

About 90 percent of those diagnosed with colon cancer survive five years or longer if the disease is diagnosed at an early stage. Once the cancer has spread to the lymph nodes, however, the five-year survival rate drops to 67 percent. If the cancer has already spread to distant parts of the body such as the liver or lungs, the five-year survival rate goes down to 10 percent.

The large intestine is the last section of the digestive tract and consists of the colon and rectum. The colon is four to six feet long, the last 12 to 15 centimeters or seven to nine inches of which is called the rectum. After food is digested in the stomach and nutrients are absorbed in the small intestine, waste from this process move into the colon, where it solidifies and remains for one or two days until it passes out of the body.

Sometimes the body produces too much tissue, ultimately forming a tumor. These tumors can be benign (not cancerous) or malignant (cancerous). In the large intestine, these tumors are called polyps. Polyps are found in about 30-50 percent of adults.

There are several different types of polyps. Inflammatory polyps, hyperplastic polyps and lymphoid polyps don't typically develop into colorectal cancer. However, researchers find that polyps called "adenomas" may undergo cancerous changes, becoming adenocarcinomas. Overall, about one percent of adenomatous polyps less than one cm in size will undergo this change, 10 percent of adenomatous polyps greater than one cm will become malignant within 10 years and 25 percent of adenomas greater than one cm will become malignant within 20 years. Furthermore, people with polyps in their colon tend to continue to produce new polyps even after existing polyps are removed.

The important fact is that colon cancers develop from adenomatous polyps by growing larger and eventually transforming into cancer; it is believed to take about 5 to 10 years for an adenomatous polyp to grow into cancer. Therefore, if appropriate colorectal cancer screening is performed, most of these polyps can be removed before they turn into cancer, effectively preventing the development of colon cancer.

Besides adenocarcinomas, there are other rare types of cancers of the large intestine, including carcinoid tumors typically found in the appendix and rectum; gastrointestinal stromal tumors found in the connective tissue of the colonic or rectal wall; and lymphomas, which are malignancies of immune cells that can involve the colon, rectum and lymph nodes.

Risk Factors

There are two risk groups for colorectal cancer: average and high-risk.

High-risk groups include those with either a personal or a family history of colorectal neoplasia (cancer or polyps), individuals with a long-standing history of inflammatory bowel disease, and people with familial colorectal cancer syndromes. Some of those at high risk may have a 100 percent chance of developing colorectal cancer.

All others are considered to be of average risk. In the average- risk individual, your risk increases throughout your life; 90 percent of colorectal cancers occur after age 50. When average-risk patients develop colorectal cancer, their cancer is considered to be sporadic (non-inherited).

The exact cause of colon cancer is unknown but it appears to be influenced both by hereditary and environmental factors.

Specific risk factors include:

Personal History: A personal history of colorectal cancer, benign colorectal polyps which are adenomas, or chronic inflammatory bowel disease (e.g., ulcerative colitis and Crohn's disease) puts you at increased risk for colorectal cancer. In fact, people who have had colorectal cancer are more likely to develop new cancers in other areas of the colon and rectum, despite previous removal of cancer.

Heredity: If one of your parents, siblings or children has had colorectal cancer or a benign adenoma, you have a higher risk of developing colorectal cancer. If two or more close relatives have had the disease, you also have an increased risk; approximately 20 percent of all people with colorectal cancer fall into this category. Your risk is even greater if your relatives were affected before age 60.

Additionally, there are two genetic conditions, familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC), which lead to colorectal cancer in about five to 10 percent of patients.

Familial adenomatous polyposis (FAP) . People who have inherited the FAP syndrome may develop hundreds to thousands of polyps in their colon and rectum at a young age, usually between ages five and 40. These polyps are all adenomas. By age 40, almost all patients with FAP will develop colon cancer if they don't have preventative surgery. Most people who have this syndrome begin annual colon examinations while in elementary school, and many choose to have their colon and rectum removed before cancer develops. FAP is rare, accounting for about one percent of all cases of colorectal cancer.

Hereditary non-polyposis colon cancer (HNPCC) . Also known as Lynch Syndrome, HNPCC is a more common form of inherited colon cancer, accounting for about three to four percent of all colorectal cancer cases. While it is not associated with thousands of polyps, polyps are present and grow more quickly into cancer than in patients without HNPCC. Colon cancer in people with HNPCC also develops at a younger age than sporadic colon cancer, although not as young as in those with FAP.

People with HNPCC often develop cancer in their 40s and 50s. Cancers in patients with HNPCC tend to be fast growing; occur more frequently in the right colon; and respond less to chemotherapy. About 70 percent of those with HNPCC will develop colorectal cancer by the age of 65.

People with HNPCC often develop cancer in their 40s and 50s. Cancers in patients with HNPCC tend to be fast growing; occur more frequently in the right colon; and respond less to chemotherapy. About 70 percent of those with HNPCC will develop colorectal cancer by the age of 65.

If you have a history of adenomas or colon cancer, or suspect you have a family history of the disease, you should discuss this with your health care professional. In some cases, you may wish to undergo genetic testing.

Age: The risk of colorectal cancer increases with age: nine in 10 new cases of colorectal cancer in the U.S. are in people over 50. Clinical studies indicate that when screened for the disease, African Americans tend to be diagnosed with colorectal cancer at a younger age than Caucasians. Menopause also is a risk factor.

Race: African Americans are more likely to get colorectal cancer than any other ethnic group. Compared to Caucasians, African Americans are 10 percent more likely to develop colorectal cancer. Unfortunately, they also are more likely to be diagnosed in advanced stages. As a result, African Americans are 40 percent more likely to die from the disease than Caucasians.

Diet: Eating a diet high in processed foods and red meats, refined grains, sweets and desserts may increase your risk of developing the disease. However, avoiding red meat and eating a low-fat diet rich in vegetables, fruit and fiber (e.g., broccoli, whole wheat bread and beans) may reduce your risk of developing colorectal cancer. Some studies suggest that getting an adequate supply of calcium and folic acid decreases the risk of colorectal cancer. Additionally, one study found that drinking eight to 10 glasses of water a day could reduce the risk of colorectal cancer by 40 percent. When it comes to alcohol, however, limit your consumption to no more than four drinks per week.

Lifestyle: Regular exercise is a key weapon in the fight against colorectal cancer. Another significant risk factor in colorectal cancer is smoking. Get help quitting if you can't do it on your own.

Screening Tests

If you are at average risk of colorectal cancer, the American Cancer Society recommends all women and men over the age of 50 to undergo one of the following:

A fecal occult blood test once a year. This must be performed on three separate occasions and you should avoid eating red meat for three days before collecting the stool samples. Your health care professional provides the necessary materials to collect the stool specimens for simple testing at home or in the office. The stool should be collected before it is in the toilet water. This test is recommended annually after age 50 and detects microscopic amounts of blood in the stool. Your health care professional may recommend this test at an earlier age or more frequently if you are at high risk for colon cancer and/or polyps.

A flexible sigmoidoscopy every five years. Preparing for this test requires administering two enemas two hours before you arrive for the exam. This examination allows the health care professional to inspect the rectum and lining of the left colon with a thin tube with a light and camera on the end. The sigmoidoscope is inserted into the rectum while you lie on your left side. This test is both diagnostic and therapeutic. However, it can detect polyps or cancer accurately in only the last two feet of the large intestine, reducing death rates from colon cancer in this portion of the colon by 60 percent. Unfortunately, the sigmoidoscopy visualizes less than half the colon and misses about half of cancers and polyps that are close to becoming cancer in the first two to three feet of the colon.

An annual fecal occult blood test (FOBT) or fecal immunochemical test (FIT) and a flexible sigmoidoscopy every five years. FIT and FOBT are similar. FIT is a stool test that also detects hidden blood (occult) in the stool performed similarly to FOBT. However, it is more thorough than FOBT and has fewer false positive results. Some forms of FIT only require two stool specimens versus three for the FOBT, and neither vitamins nor foods will affect FIT results (these things can affect results of a FOBT); therefore, no dietary restrictions are necessary prior to collecting the stool samples. Similar to FOBT, the FIT test will not detect a tumor that is not bleeding, so a colonoscopy may be necessary for further screening or if cancer is suspected.

(Of these first three options, the combination of FOBT or FIT every year plus flexible sigmoidoscopy every five years is preferable.)

A double contrast barium enema every five years. This test involves injecting barium (a liquid imaging agent that shows up during an x-ray) through the rectum into the colon, then taking x-rays of the colon. A health care professional injects the thick, chalky liquid through a small tube inserted into your anus. You may feel an urge to move your bowels, but should hold on while the x-rays are taken. After the x-rays finish, you can expel the liquid. To avoid becoming constipated afterward, you should drink plenty of fluids to flush the barium from your system. While the procedure can be uncomfortable, it is not usually painful. This test is only a diagnostic test. If abnormalities show up on the x-ray, a colonoscopy must be performed. The barium enema is not a very sensitive test and misses half of polyps that are larger than 1 centimeter.

A colonoscopy every 10 years. Similar to the flexible sigmoidoscope, the colonoscope is a longer thin black tube that allows the health care professional to examine the entire large intestine. Preparation for the procedure requires drinking a laxative recommended the day before the colonoscopy. Adequate preparation is critically important to enable the physician to visualize the entire lining of the colon. Leftover stool obscures the view of that portion of the colon and could lead to missing lesions. The ACS recommends getting a colonoscopy starting at age 50 for the average-risk person or if a FOBT or FIT shows blood in the stool. You typically receive a mild sedative before the procedure, so you should experience minimal discomfort. The procedure itself lasts 15 to 30 minutes.

This test is both diagnostic and therapeutic. It detects both polyps and cancers found anywhere in the colon. Any polyps or other growths found during this examination are usually removed and sent to a laboratory for examination. Medicare now covers this procedure for people over 50 who are considered to be at average risk for developing colon cancer. Women and men over 50 should have a colonoscopy at least every 10 years. The American College of Gastroenterology recommends that African Americans, who tend to develop the disease at a younger age than other races, begin screening by colonoscopy at age 45.

Virtual colonography. This is a relatively new technique that uses a CT scan to create a three-dimensional image to evaluate the bowel. Not many medical centers have the technology to perform this exam, which is for diagnostic purposes only and the technology is still undergoing development. It does not allow for a biopsy or polyp removal if any abnormalities are found. Most insurance companies do not cover virtual colonography as screening for colorectal cancer.

Most women find sigmoidoscopies and colonoscopies much more tolerable than they expect. Worrying about the process and undergoing the necessary preparation beforehand are often more unpleasant than the exam itself.

Other tests that your health care provider might perform include:

Digital rectal examination (DRE). Your health care professional inserts a gloved finger into the rectum to feel for any abnormalities. This simple test, which is not painful, can detect many rectal cancers. However, even the longest of fingers are far too short to examine the full length of the large intestine. For this reason, other tests and examinations, such as the FOBT, flexible sigmoidoscopy, and colonoscopy must be used. The rectal exam is not sufficient to screen for colon cancer.

Genetic testing. The few hereditary cancer syndromes mentioned here are rare but are associated with mutations in specific genes. These mutations can be passed on to other family members. Thus, if your family is affected or may be affected by one of these syndromes, you may need to undergo genetic testing. If genetic testing and counseling are done properly, lives can be changed dramatically, both in terms of preventing colon cancer and lessening the psychological impact of knowing you are predisposed to the disease.

Genetic testing for colon cancer raises may scientific and ethical issues. Although tests are available to identify the mutations that may predispose you for colon cancer, they are not absolutely positive predictors. Additionally, many health care professionals are not yet fully educated about the tests, and may misinterpret the results.

Thus, if you have a strong family history for colon cancer, you should be seen at a genetic screening center. To locate a center, check out hereditary colorectal cancer Web sites such as

If there is a reason to suspect that you have colorectal cancer, your health care professional will take a complete medical history and perform a physical examination as part of an initial evaluation or "work-up."


Symptoms of colorectal cancer include:

Change in bowel habits (diarrhea, constipation or narrow stools for more than a few days)

Urgency for a bowel movement or feeling like you need to move your bowels even if you just did.

Blood in the stool

Stomach pain

Weakness and/or fatigue

Contact your health care professional if you experience one or more of these symptoms.


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Keywords: colon cancer, colorectal cancer, women, survival rate, polyps, adenomas, colon and rectum, develop colorectal cancer, symptoms, blood in the stool
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Publication:NWHRC Health Center - Colon Cancer
Article Type:Disease/Disorder overview
Date:Sep 7, 2006
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