Colorectal polyps are growths that reside in the lining of the colon (large intestine) or rectum. It is believed that most colorectal cancers start as a small colorectal polyp known as an adenoma. Over time, an adenomatous polyp may develop signs of abnormal growth know as dysplasia. The greater the amount and degree of dysplasia a polyp has, the more likely it is to turn malignant (cancer). If an adenomatous polyp becomes cancerous, it usually grows and develops worsening dysplasia over the course of years. However, not all adenomatous polyps will turn cancerous and there are currently no known means of determining which adenomatous polyps will become cancerous and which will not. Therefore, it is recommended that all adenomatous polyps be removed. Removal of colorectal polyps is key in preventing colorectal cancer. Studies have shown that the removal of polyps (polypectomies) results in a decrease in the development of colorectal cancer.
WHAT CAUSES A POLYP TO FORM?
The cause of polyps is uncertain, but genetic and lifestyle factors appear to contribute to polyp development. Genetic factors may determine a person's susceptibility to colorectal cancer, whereas dietary and other lifestyle factors may determine which at-risk individuals develop polyps. Diets high in fat and low in fruits and vegetables may increase the risk of polyps. Lifestyle factors such as cigarette smoking, excessive alcohol consumption, obesity, and a sedentary lifestyle may also increase the risk. Some polyps are the result of hereditary conditions, such as familial adenomatous polyposis and Peutz-Jeghers syndrome. Individuals with hereditary conditions may have multiple polyps form and may develop colorectal cancer at a younger age if the polyps are not removed.
Most polyps produce no symptoms. When they do, the most common symptom is bleeding from the rectum, which may be visible as bright red blood. Blood may also be hidden in the stool and can only be detected by stool testing or recognized as anemia on a blood test. A large polyp can cause cramps, abdominal pain or obstruction. A physician may be able to feel rectal polyps by inserting a gloved finger into the rectum, but typically polyps are discovered during a colonoscopy (examination of the large intestine with a viewing tube). The American Society for Gastrointestinal Endoscopy (ASGE) recommends that colorectal cancer screening begin at age 50, or sooner if there is a family history of colorectal cancer or if other risk factors are present. Colonoscopy is considered the gold standard of colorectal cancer screening methods for its ability to both detect and remove polyps during the same procedure.
Colorectal polyps are diagnosed by evaluation of the inside of the colon and rectum. A colonoscopy is a test that allows examination of the large intestine using a flexible tube (colonoscope) that is equipped with a camera that visualizes the intestinal wall. The colonoscopist has the ability to take tissue samples and remove colorectal polyps. Colonoscopy is the only screening method that is both diagnostic and therapeutic. There are other methods that can directly or indirectly look for colorectal polyps, including CT colonography (also known as virtual colonoscopy) and double contrast barium enema.
Several endoscopic techniques and imaging methods to improve the detection of flat polyps are currently under investigation (see FAQ on flat polyps for more information). The use of special stains (chromoendoscopy) to enhance recognition of colorectal polyps is one of these methods. Several studies are evaluating the use of chromoendoscopy as a tool in recognizing colorectal polyps in individuals with a high risk for colorectal cancer. In addition, new colonoscopic imaging methods that enhance evaluation of surface patterns of the lining of the intestine (narrow band imaging) or penetrate beyond the surface (autoflorescence) are currently under investigation. For most individuals, the use of enhanced colonoscopic methods is not necessary. (See media backgrounder on high definition scopes for more information.)
There are other key factors proven to be important for identifying polyps during a colonoscopy including bowel preparation, length of time for colonoscopic examination, and experience and training of the endoscopist. Patients must take the full bowel preparation as directed by their physician before a colonoscopy. Proper bowel preparation is important so that the physician can clearly see the entire colon. According to ASGE guidelines, physicians performing a colonoscopy should have an average withdrawal time of six minutes or more for a thorough exam. A qualified physician to do colonoscopy should have specific training in endoscopy and be board certified. To find a qualified gastrointestinal endoscopist in your area, go to the “Find a doctor” link at www.asge.org.
If a polyp is discovered during a colonoscopy, the physician will most likely take a tissue sample or entirely remove the polyp during the same examination. Doctors generally recommend removing all polyps from the large intestine and rectum because of the potential of some polyps to become cancers. Polyps are removed during a colonoscopy procedure using a cutting instrument or an electrified wire loop called a snare. If a polyp cannot be removed during colonoscopy due to size or anatomical location, an ink tattoo may be placed at the site and surgery may be required for the polyp’s removal. During a colonoscopy, the patient is sedated and comfortable. Most patients are not even aware that the procedure has taken place afterward.
If a polyp is found to be a cancer, treatment depends on whether the cancer is likely to have spread. The risk of spread is determined by microscopic examination of the polyp by a pathologist. If the risk is low, no further treatment is necessary. If the risk is high, particularly if the cancer has invaded beyond the superficial layers of the polyp, the affected segment of the large intestine may need to be removed surgically. Removal of colorectal polyps does prevent a cancer from developing at that one location, but the patient may be at risk to develop polyps at other locations. Close follow-up is indicated for these patients. When a person has a polyp removed, the entire large intestine and rectum are examined by colonoscopy at regular intervals as determined by the number and type of polyps identified.
ARE THERE ANY FOODS OR HABITS THAT CAUSE COLORECTAL POLYPS AND CANCER?
There are no foods that directly cause colorectal cancer. However, studies of different populations have identified associations that may affect an individual’s risk of developing colorectal cancer, or the precancerous lesions called polyps. Smoking clearly increases the risk of colorectal cancer and other cancers. Studies have shown a slight increased risk of developing colorectal cancer among individuals with higher red meat or non-dairy (meat-associated) fat intake.
Studies have also shown that getting an adequate amount of calcium and vitamin D in the diet or from supplements can reduce the risk of polyps. A plant based diet that is high in fiber may also help reduce the risk of colorectal cancer. Use of aspirin and NSAIDs (such as celecoxib and sulindac) have been proven to decrease the risk of colorectal polyps. However, the use of these agents is reserved for individuals at high risk for colorectal polyps and cancer.
Ongoing studies evaluating the role of vitamins and other natural products are underway to examine their role in colorectal polyp prevention. Although few studies have been able to show definitively that modifying lifestyle reduces the risk of colorectal polyps or cancer, lifestyle changes such as reducing dietary fat, increasing intake of fruits and vegetables, ensuring adequate vitamin and micro-nutrient intake, and exercise, will all improve general health. Regardless of your dietary and lifestyle habits, screening for colorectal polyps is the key in preventing colorectal cancer.
For more information about colorectal cancer screening or to find a qualified doctor in your area, visit ASGE's colorectal cancer awareness Web site at www.screen4coloncancer.org.
Reviewed November 2010