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Definition Of Colon Cancer

Definition

The digestive system is made up of the esophagus (food pipe), stomach, and the small and large intestines. The upper 5 - 6 ft (1.5-1.8 m) of the large intestine is called the colon, and the last 6 - 8 in (15-20 cm) of the colon is the rectum. Colorectal cancer is a disease in which the cells of the tissues lining the colon and the rectum start to grow uncontrollably and form tumors.

Description

Colorectal cancer is the third most common cancer, behind lung and prostate cancer in men, and breast and lung cancer in women. The American Cancer Society (ACS) estimates that colorectal cancers will account for about 11% of all new cancer cases in 1998. They will result in about 10% of all cancer deaths. The incidence of colorectal cancer is divided equally among both men and women, with the risk usually beginning after 40 years of age. The average age at first diagnosis is 60-65 years.

The main function of the colon is to absorb water and the nutrients from the food already digested by the stomach and the small intestine. The waste material left behind goes into the rectum. From here, it is excreted out of the body through the anus. The colon has four sections. The ascending colon moves upward to the hepatic flexure. It then becomes the transverse colon moving across to the liver. When reaching the spleen, the colon continues as the descending colon and moves down to the pelvis area. It is then called the sigmoid colon and extends to the rectum. Cancer can develop in any of the four sections or in the rectum (the last part of the colon). Cancers beginning in the different sections have different symptoms.

Colorectal cancers have a very high cure rate if found early. Unfortunately, most colorectal cancers are "silent tumors." They grow slowly and often do not produce symptoms until they reach a large size. Therefore, diagnosis is often delayed. The cancer usually begins as a benign growth in the lining of the intestine. These benign growths are called polyps. Most of the polyps are not cancerous. Nevertheless, virtually all colorectal cancers begin from these benign growths. There are two kinds of polyps, hyperplastic polyps that are small and completely benign. They do not ever develop into cancers. The second kind of polyps, called adenomas, have the potential to become cancerous.

Causes & symptoms

While we do not know the exact cause of most colorectal cancers, the risk factors that makes a person more susceptible to colorectal cancer are:

• Family history: Some rare disease conditions such as Familial Adenomatous Polyps (FAP) and Lynch syndrome (a genetic condition that predisposes certain families to colon cancer, even when polyps are not present) are present in certain families and may make an individual more likely to develop cancer of the colon or the rectum. Inheriting defective genes causes approximately 10% of colorectal cancers.
• History of colorectal cancer: Even when colorectal cancer has been completely removed, new cancers may still develop in other areas of the colon and the rectum.
• Recurrent intestinal polyps: Polyps are benign growths in the colon or rectum. While most polyps are harmless, some particular types do increase the risk of colorectal cancer, especially if they are large and there are many of them.
• Inflammatory bowel disease: Chronic ulcerative colitis, a condition in which the colon is inflamed over a long period of time and causes ulcers in the lining, can increase the risk of colon cancer.
• Age: About 90% of colorectal cancers are found in people over the age of 50.
• Diet: Eating foods that are high in fat and low in fiber may increase the risk of colorectal cancer.
• Physical inactivity: A sedentary lifestyle and not enough physical activity has been reported to be associated with a higher risk of colorectal cancer.

The earliest sign of colon cancer may be bleeding. Most of the tumors bleed only small amounts and the bleeding is occasional. Evidence of the blood is found during chemical testing of the feces for hidden (occult) blood. This is called fecal occult blood test. When tumors grow to a large size, they may cause a change in the bowel habits. The stools may be very narrow in diameter. There may be other symptoms of general stomach discomfort, such as a feeling of fullness or bloating, stomach cramps, gas pains, diarrhea or constipation. Sometimes the patient complains of a feeling that the bowel does not empty completely. Constant tiredness and weight loss with no known reason may be other warning signs. Many of these symptoms can be caused by conditions other than cancer, however they must be evaluated by a doctor without delay.

Diagnosis

If the doctor suspects colon cancer, then he or she may use one of the following tests to find out if the disease is present. A thorough physical examination will be conducted to check all symptoms and a complete medical history will be taken to assess any risk factors. A digital rectal examination will be done during the physical. In this procedure, the physician inserts a gloved finger into the rectum to feel for anything abnormal. This simple test can help to detect many rectal cancers. A fecal occult blood test may be ordered, where a sample of stool is examined for blood. The test kit can be purchased at any local pharmacy. The test involves taking a sample of stool and smearing it on a slide. This is then sent to the laboratory or to the doctors' office where it will be chemically examined for the presence of red blood cells.

A sigmoidoscopy may be done to enable the doctor to look inside the rectum and part of the colon. In this procedure, a thin flexible hollow lighted tube (sigmoidoscope) is placed into the rectum. The doctor then looks inside the scope for small growths called polyps. Since they may become cancerous, they should be removed.

A colonoscopy will be ordered if the doctor wishes to examine the entire colon lining. A colonoscope is longer than a sigmoidoscope and is inserted through the rectum into the colon. It is connected to a video camera and a video display unit so that the doctor can look at the inside of the colon. If a suspicious mass is detected, then the doctor may cut out a small piece to examine it under a microscope and see if there are any cancer cells. This procedure is called a biopsy.

Another test that is used to diagnose colon cancer is known as a double contrast barium enema. The patient is given a barium sulfate enema through the anus. This is a chalky substance that partially fills and opens the colon. When the colon is about half full of barium, the patient is turned on the x-ray table so that the barium spreads throughout the colon. Air is then inserted into the colon to make it expand and x-ray films are taken.

Treatment

Treatment for colon and rectal cancers depend on the stage of the cancer (the extent to which it has spread). The standard modes of treatment are surgery, radiation therapy and chemotherapy.

Surgery is the main treatment for colon cancer. If the cancer is found at a very early stage, the doctor may take out the cancer without cutting into the abdomen. Instead the doctor may put a tube through the rectum into the colon and cut the tumor out. This procedure is called a local excision. If the cancer is found in a polyp, the operation is called a polypectomy. If the cancer is larger but confined to a portion of the colon, the abdomen is opened up and the cancerous growth and a small piece of normal tissue from either side of the cancer is removed. This procedure is called segmental resection. If there is any likelihood of the cancer having spread to the nearby lymph nodes, they may be removed as well. The remaining sections of the colon are then attached back together.

If the doctor is not able to sew the colon back together, he will make an opening called the stoma on the outside of the body for the waste material to pass out of the body. This is called a colostomy. Sometimes the colostomy is temporary until the colon is healed and then it can be reversed. However, if the surgery involves taking out the entire lower colon, a permanent colostomy is needed. The patient will need to wear a special bag to collect body wastes. This bag attaches to the body around the opening (stoma) with a special glue and can be thrown away after it is used. The bag is hidden by the clothing. The hospital personnel will educate the patients on how to take care of these bags themselves.

In the case of rectal cancer, different surgical methods are used. When the cancer is found in the polyps, a procedure known as polypectomy is used. Local excision is a procedure that can be used to remove small superficial cancers. A small amount of adjoining tissue is also removed from the inner layer of the rectum. If the cancer is in the deeper layers of the rectum, local full thickness resection is used. A cut is made through all the layers of the rectum to remove the invasive cancer as well as some surrounding normal rectal tissue. Electrofulguration is a procedure where the cancer is burned by passing an electric current through it. All of these methods can be done without cutting through the abdomen.

Radiation therapy involves the use of high-energy radiation to kill cancer cells. It can be applied to both colon and rectal cancers. External beam radiation uses radiation from an external source that is focused on the tumor. Internal radiation therapy uses a small pellet of radioactive material that is implanted directly into the cancer. Radiation therapy is generally used as adjuvant therapy, that is, it is used after the surgery to destroy any cancerous material that may not have been removed during surgery. If the tumor is in a place that makes surgery hard, then radiation may be used before surgery to shrink the tumor. In advanced cancers, where surgery is not an option, radiation may be used to ease the symptoms such as pain, blockage or bleeding.

In colorectal cancers, chemotherapy is generally used after surgery to destroy any cancerous cells that may have migrated from the original site and spread to other parts. The anti-cancer drugs are either given through a vein in the arm or by mouth, in the form of pills. In the case of advanced cancers, chemotherapy may be given to alleviate symptoms.

Prognosis

The death rate from colorectal cancer has been going down for the past 20 years. This may be because of the advanced methods of early detection and improved treatment modes.

If colorectal cancer is detected at an early stage and if treated appropriately, 92% of the people will survive 5 years or more. However, only a third of colorectal cancers are found at that early stage. Once the cancer has spread to nearby organs or lymph nodes, the 5-year survival rate goes down to 64%. If the disease has metastasized (spread) to distant sites such as the liver or the lung, the outlook is not good, with only 7% of the patients surviving 5 years after initial diagnosis.

Prevention

Although the exact cause of colorectal cancer is not known, it is possible to prevent many colon cancers by avoiding the risk factors. By following the screening guidelines, the number of colon cancer cases can be lowered, and by detecting the disease at an earlier stage, the death rate can be lowered.

The American Cancer Society recommends that beginning at age 50, both men and women should follow the schedule for early detection of colorectal cancer. This includes a yearly fecal occult blood test, and an annual digital rectal examination. Flexible sigmoidoscopy should be done every 5 years, and a colonoscopy every 5 - 10 years. A barium enema x ray should also be done every 5 - 10 years.

Proper diet and exercise go a long way in preventing colorectal cancer. The American Cancer Society recommends eating at least five servings of fruits and vegetables every day and six servings of food from plant sources such as breads, cereals, grain products, rice, pasta, or beans. Avoiding high-fat, low-fiber foods, such as red meat and processed foods, is also advised. Achieving and maintaining an ideal body weight by at least 30 minutes of physical activity every day is recommended.

If polyps are detected during a regular screening examination, they should be removed. Since some of the polyps may develop into colorectal cancers, removing them can lower a person's risk and prevent some cancers before they are fully formed.

It may not be possible to control risk factors such as a strong family history of colorectal cancer. However, by getting information about prevention and early detection, one can still beat the odds. People with a family history of colorectal cancer should start screening at a younger age and it should be done more frequently. Certain genetic tests are now available that can help determine which members of certain families have inherited a high risk for developing colorectal cancer.

Key Terms

Adenomas

Polyp-like growths in the colon or the rectum that have the potential to turn cancerous.

Barium enema

An x-ray test of the bowel after receiving an enema of a white chalky substance that outlines the colon and the rectum making them more visible in an x ray.

Benign

Tested tissue that is not cancerous, does not invade surrounding tissue or spread to other parts of the body.

Biopsy

Removal of a tissue sample for examination under the microscope to check for cancer cells.

Chemotherapy

Treatment with drugs that destroy cancerous tissue.

Colonoscopy

A medical procedure in which the doctor looks at the colon through a flexible lighted instrument called a colonoscope.

Colostomy

An opening created by a surgeon in which the colon leads to the outside of the body. A colostomy provides a path for waste material to leave the body after the colon has been removed.

Crohn's disease

A chronic inflammatory disease where the immune system starts attacking one's own body. The disease generally starts in the gastrointestinal tract.

Digital rectal examination

An exam to detect rectal cancer. The doctor inserts a lubricated gloved finger into the rectum and feels for abnormal areas.

Familial Adenomatous Polyps (FAP)

An inherited condition in which hundreds of polyps develop in the colon and rectum.

Fecal occult blood test

A test where the stool sample is chemically tested for hidden (occult) blood.

Flexible sigmoidoscopy

An examination in which the doctor looks at the lower portion of the colon.

Hyperplastic polyps

Benign polyps found in the colon or the rectum.

Lynch syndrome

A genetic condition that predisposes certain families to colon cancer, even when polyps are not present.

Polypectomy

A surgical procedure that involves removal of the polyp.

Polyps

An abnormal growth that develops on the inside of a hollow organ such as the colon.

Radiation therapy

Treatment using high-energy radiation from x-ray machines, cobalt, radium, or other sources.

Segmental resection (colon)

Surgical removal (excision) of a portion of the colon.

Stoma

The opening established in the abdominal wall by the colostomy procedure.

Ulcerative colitis

A chronic condition where recurrent ulcers are found in the colon. It is manifested clinically by abdominal cramping, and rectal bleeding.

Further Reading

For Your Information

Books

• Berkow, Robert et al., eds.Merck Manual of Diagnosis and Therapy.16th edition. Merck Research Laboratories, 1992.
• Dollinger, Malin. Everyone's Guide to Cancer Therapy. Somerville House Books Limited, 1994.
• Morra, Marion E.Choices. Avon Books, October 1994.
• Murphy, Gerald P.Informed Decisions: The Complete Book of Cancer Diagnosis, Treatment and Recovery. American Cancer Society, 1997.

  Organizations

• American Cancer Society (National Headquarters). 1599 Clifton Road, N.E. Atlanta, GA 30329. (800) 227-2345. http://www.cancer.org.
• Cancer Research Institute (National Headquarters). 681 Fifth Avenue, New York, NY 10022. (800) 992-2623. http://www.cancerresearch.org.
• National Cancer Institute. 9000 Rockville Pike, Building 31, Rm 10A16, Bethesda, MD 20892. (800) 422-6237. http://wwwicic.nci.nih.gov.
• Oncolink. University of Pennsylvania Cancer Center. http://cancer.med.upenn.edu.
• United Ostomy Association, Inc. (UOA). 36 Executive Park, Suite 120, Irvine, CA (800) 826 0826.

  Other

• NCI/PDQ Patient Statement, "Colon Cancer." National Cancer Institute.
• NCI/PDQ Patient Statement, "Rectal Cancer." National Cancer Institute.
• 1998 Cancer Facts and Figures. American Cancer Society.

Gale Encyclopedia of Medicine. Gale Research, 1999.