Colon Polyps

What is a colon polyp?

Colon polyps are fleshy growths that occur on the inside (the lining) of the large intestine, also known as the colon. Polyps in the colon are extremely common, and their incidence increases as individuals get older. It is estimated that 50% of the people over the age of 60 will harbor at least one polyp. The significance of polyps is that we know that when certain types of polyps grow large enough, they can become cancerous, and, moreover, colon cancer is the second leading cause of death from cancer in the United Sates. Therefore, screening for colon polyps and removing them before they become cancerous should markedly reduce the incidence of colon cancer.

What types of polyps become cancerous?

The polyps that become cancerous are called adenomatous polyps or adenomas. Adenomas account for approximately 75% of all colon polyps. There are several subtypes of adenoma that differ primarily in the way the cells of the polyp are assembled when they are examined under the microscope. Thus, there are tubular, villous, or tubulo-villous adenomas. Villous adenomas are the most likely to become cancerous, and tubular adenomas are the least likely.

Are there other factors that determine a polyp's chance of becoming cancerous?

Another factor that contributes to a polyp's likelihood of becoming cancerous is its size. The larger a polyp grows, the more likely it is to become cancerous. Once a polyp reaches two centimeters or approximately one inch in size, the risk of cancer is in excess of 20 percent. Therefore, it is advisable to remove polyps of any size, preferably when they are of a small size, to prevent their growth and progression to cancer.

What other types of polyps are there in addition to adenomas?

Although adenomas are by far the most common type of colon polyps, there are several other types of polyps. Among the other types of polyps that have no malignant potential are the hyperplastic, inflammatory, and hamartomatous polyps.

What are the guidelines for screening individuals for polyps in order to prevent colon cancer?

Knowing that colon polyps grow and go on to become cancerous and knowing how common they are, screening guidelines have been set by the American Cancer Society to minimize the risk of colon cancer by detecting and removing polyps.
Starting at the age of 40, everyone should have a stool specimen tested for occult blood (blood that cannot be seen with the naked eye) every year. This is recommended because it is known that when polyps become large they can bleed into the intestine where the blood mixes with the stool. Thus, an early warning sign for colon polyps could be the presence of occult blood in the stool.

Starting at the age of 50, everyone should have a flexible sigmoidoscopy every 3-5 years. A flexible sigmoidoscope is a two and one-half foot tube half an inch in diameter with a light on the end that can be inserted through the anus for inspecting the inside of approximately one-third of the colon's total length.

If adenomatous polyps are detected with sigmoidoscopy, then a full colonoscopy with a longer tube (four to five feet) should be used to inspect the entire length of the colon. During a colonoscopy, any polyp can be removed and sent for an evaluation under the microscope to determine if it too is an adenomatous polyp.

Many doctors in the US are recommending screening colonoscopies rather than flexible sigmoidoscopies for healthy subjects with an average risk for developing colon cancer. Colonoscopies are recommended beginning at the age of 50 and thereafter every 7-10 years if no colon polyps or cancers are found.

The rationale for this recommendation is: 1) Colonoscopy examines the entire colon while flexible sigmoidoscopy only examines the rectum and the colon adjacent to the rectum, 2) approximately 50% of colon polyps (and colon cancers) are found in the upper colon (cecum, ascending colon, and transverse colon) and, therefore, are beyond the reach of sigmoidoscopes and would be missed by flexible sigmoidoscopy, and 3) the National Polyp Study, a large, scientific study, has shown that colonoscopy with removal of all colon polyps reduces deaths from colon cancer.

What kind of additional surveillance should be done once a polyp has been found?

Surveillance after polyps are found depends on the number and type of polyp that are found. If the polyp is not an adenoma, then follow- up with colonoscopy is not necessary. If only one polyp is found and it is a tubular adenoma less than 1 centimeter in size, then repeating the colonoscopy after five years is appropriate (Unless the individual has had a first degree relative with colon cancer in which case three years would be appropriate.)

If a first or subsequent colonoscopy finds three or more adenomas, the next colonoscopy should be between one and three years later. If a polyp is flat (sessile) and, therefore, is more difficult to remove completely, then the site of the removal should be checked in 3-6 months to document complete removal and then again one year later.
Once a normal colonoscopy without polyps is performed, the surveillance interval can be increased to five years.

What happens if a polyp that is removed contains cancer?

These polyps may be treated without surgical removal of that part of the colon that contained the polyp if: 1) the doctor is confident that the polyp was removed completely, 2) the pathologist does not see any cancer at the margin of the polyp that was attached to the colon (which would suggest that cancer was left behind), and 3) the cancer is histologically (under the microscope) "less aggressive" looking.

Is one's risk of having colon cancer increased by having had an adenoma?

An individual's risk of colon cancer is approximately double the general population once an adenomatous polyp is found. This individual's risk of developing colon cancer can be significantly reduced by removing the polyp and any future polyps.

What is one's risk of having a polyp or cancer if a first- degree relative (parent, sibling, or child) has had an adenomatous polyp?

An individual with a first degree relative with an adenomatous polyp would have a 50% (one and one-half times) greater risk of developing colonic cancer than an individual without a relative with polyps. The risk for adenomatous polyps is not known. The current estimate is that 6% of the general population-which includes individuals with relatives with and without polyps--will develop colon cancer.

Are there ways to prevent colon polyps from developing?

First of all, there are dietary recommendations that can be made. We know that diets high in fat and low in fiber predispose an individual to develop colon polyps. This probably is why the incidence of colon polyps is much higher in developed countries such as the United States and Europe where diets are high in fat and low in fiber. A recent study, however, did not confirm that high fiber prevents colon polyps or cancer. We know that certain vitamins protect against colon cancer, namely vitamins C and E. In addition, certain cruciferous vegetables such as broccoli and cauliflower protect against colon cancer. Non-steroidal anti-inflammatory medications, such as aspirin reduce the formation of polyps, although non-steroidal medications are not advocated as a means to prevent colon polyps.

What does the future hold for screening and surveillance of colon polyps?

Effort presently is being expended to develop a radiologic colonoscopic test. This is a means by which CAT scan imaging can be used to evaluate the colon for the presence of colon polyps. Preliminary studies have shown this to be relatively accurate in detecting the presence of polyps in the colon. Obviously, the limitation of this study is that polyps, once found, cannot be removed immediately but must be done at a later colonoscopy with a flexible colonoscope. Therefore, the role of the radiologic colonoscopy may be limited to simply screening populations at lower risk for the presence of polyps, and only those individuals found to harbor polyps would be sent for colonoscopic excision of the polyps. Also on the horizon are blood tests, which may determine the genetic risk for polyps. If the test discloses genes that are associated with a high risk for colon cancer, then the individual may enter a program of colonoscopic screening.

Are there situations in which polyps carry a very high risk of becoming cancerous?

Defective genes cause colon polyps and colon cancers. Individuals who have inherited colon cancer causing gene defects are at high risk of developing colon polyps and caners early in life. The human body is composed of trillions of cells. Inside each cell are two sets of 23 chromosomes; one set is inherited from each parent. Each chromosome contains long strands of DNA that are comprised of thousands of genes strung together. The genes carry the genetic information that is passed down from both parents. Different segments of the DNA strands contain genes responsible for different structures and functions in the body. For example, certain segments of DNA carry genes that determine one's eye color, hair color, height, and other physical characteristics. Other DNA segments of DNA carry genes that regulate the duplication and the rate of growth of cells. Still other genes prevent cells from organs within the body from invading neighboring organs or spreading to distant organs.

When chromosomes are damaged, genes become defective. When genes that normally prevent cells from multiplying and growing are defective, the cells containing the defective genes can multiply and grow without restraint. When cells grow without restraint inside the colon, a colon polyp develops. When additional genetic defects occur in that polyp, the polyp can turn cancerous and invade adjacent tissue and /or spread to distant organs.

Genetic damage (damage to individual genes) can be inherited from either parent or can be acquired after birth when normal genes in normal cells become damaged by environmental factors such as radiation, chemicals, oxidants, viruses, etc. Inherited genetic defects are present in every cell in the body, whereas acquired defects are present only in the cells that are damaged and the cells they produce, for example, in the cells of the polyp or cancer.

Generally, acquired genetic defects tend to cause only one or a few colon polyps that can be removed by colonoscopy. (For further information, please see the articles on colonoscopy.) Removing these polyps effectively prevents the progression from colon polyp to colon cancer. On the other hand, inherited genetic defects that are present in every cell have a tendency to cause numerous (sometimes thousands) of colon polyps. These polyps may be too large or too numerous to be removed by colonoscopy. In addition, the progression from polyp to invasive cancer may be so rapid that even frequent colonoscopy is not adequate to remove polyps and prevent colon cancer. Finally, some cancers may develop directly from cells of the colon lining without the development of polyps that can be recognized and removed. For all of these reasons, among patients with inherited genetic defects that cause colon cancer, surgical removal of the colon is necessary to prevent colon cancer.

Hereditary colon cancer syndromes are caused by specific inherited mutations that are sufficient in themselves to cause colon polyps, colon cancers, and non-colonic cancers. Hereditary colon cancer syndrome can affect multiple members of a family. Approximately 5% of all colon cancers in the US are due to hereditary colon cancer syndromes. Patients who have inherited one of these syndromes have an extremely high risk for developing colon cancer, approaching 90%-100%. Fortunately, blood tests are now available to test for these hereditary colon cancer syndromes, once a syndrome has been suspected within a family.

Familial adenomatous polyposis (FAP) syndrome is an example of a hereditary colon cancer syndrome, characterized by thousands of adenomatous polyps forming in the colon, with colorectal cancer an inevitable consequence. This usually occurs 10 to 15 years after the onset of polyps, which most often begins at puberty. The average age of diagnosis of familial polyposis is 25 years of age, with cancers developing at age 20 to 30. In this syndrome, polyps also can be present in the stomach, duodenum and the terminal ileum. The basis of this disease seems to be a genetic abnormality on chromosome number five.

A variant of the familial adenomatous polyposis syndrome is Gardner's syndrome. These patients also develop thousands of adenomatous colonic polyps. What distinguishes these two syndromes from one another is that Gardner's syndrome is associated with extra- colonic manifestations, including bony tumors of the mandible, skull, and long bones, as well as fatty, fibrous, and mixed tumors, which may occur anywhere in the body.
Another familial polyposis syndrome is Turcot's syndrome, a variant of familial adenomatous polyposis in which there are fewer colon adenomas.

The Lynch syndrome also is known as hereditary non-polyposis colorectal cancer (HNPCC). In the Lynch syndrome individuals do not form multiple colon polyps as other individuals with the other hereditary colon polyp syndromes. Nevertheless, they are at high risk for developing colon cancer. The syndrome is inherited, and because it is inherited in an autosomal dominant manner, cancer is very common within families with this syndrome. Lynch syndrome has been broken down into Lynch syndrome I, and Lynch syndrome II, with Lynch syndrome II involving the same risk of colon cancer as Lynch I, but in addition, cancers outside the colon as well, particularly in the uterus, ovaries, and breast. In both Lynch syndromes, colon cancer usually develops at a young age (40-50 years) and more often occurs on the right side of the colon where it cannot be found by sigmoidoscopic examination. Surveillance for all family members should include twice-yearly fecal occult blood testing and yearly colonoscopy, beginning at an age 10 years younger than the age at which the youngest family member has developed cancer or at age 20 if this information is not available.

What about genetic counseling and testing?

Patients who have hereditary colon cancer syndromes usually have no symptoms and are unaware that they have colon polyps or early colon cancers. They usually will develop colon cancers early in life (often before ages 40-50). Therefore, to prevent colon cancers in patients with hereditary colon cancer syndromes, colon screening must begin early. For example, patients with FAP should have annual flexible sigmoidoscopies starting at age 12, patients with AFAP should have annual colonoscopies starting at age 25, and patients with HNPCC should have colonoscopies beginning at age 25 (or 10 years younger than the earliest colon cancer diagnosed in the family, whichever is earlier). The current screening recommendations for the general population (fecal occult blood testing, flexible sigmoidoscopy, and colonoscopy beginning at ages 40-50) are inadequate for most patients with hereditary colon cancer syndromes.

Genetic counseling and testing are important to identify patients and family members with hereditary colon cancer syndromes so that screening with flexible sigmoidoscopies and colonoscopies can begin early and, if necessary, the colon can be removed surgically to prevent colon cancer. Moreover, depending on which hereditary colon cancer syndrome is present, early screening for other types of cancer such as ovarian, uterine, stomach, ureter, and thyroid may be appropriate.

Colon Polyps At A Glance

• Colon polyps are growths on the inside of the colon.
• Colon polyps that often become cancerous are called adenomas or adenomatous colon polyps.
• The risk of an adenomatous colon polyp becoming cancerous increases as the size of the polyp increases.
• All individuals should have screening flexible sigmoidoscopy beginning at age 50 to detect colon polyps.
• If colon polyps are found during flexible sigmoidoscopy, colonoscopy should be done to detect colon polyps elsewhere in the colon.
• Increasingly, doctors in the US are recommending screening colonoscopy rather than flexible sigmoidoscopy for all individuals starting at age 50
• Individuals who have had adenomatous polyps need regular screening with colonoscopy to detect and remove new polyps.
• Genetic testing and counseling is now available to identify individuals with inherited colon cancer syndromes so that screening flexible sigmoidoscopies and colonoscopies can begin early to detect polyps and prevent the development of early colon cancers.