Cancer & Polyps
Colorectal Cancer is the second leading cause of cancer death in the United States. The disease strikes both men and women and like any other type of cancer or disease, prevention or early detection is paramount in the treatment of the disease.
Colon polyps are growths that arise from the inner lining of the colon. While most polyps are benign, some may grow to become cancerous. The risk of cancer transformation depends on the type and size of the polyp. The risk varies from a few percent to 40 percent.
The actual cause of polyps is not known, but may be related to dietary or hereditary factors. Diets high in fiber and low in animal fats reduce the likelihood of colon polyps and cancer.
Polyps are most frequently identified by screening sigmoidoscopy or barium enema. If polyps are found on these tests, a complete colonoscopic evaluation is recommended. Removal of the polyp(s) prevents transformation to cancer.
After polyp removal, periodic follow up examinations are needed to detect the growth of new polyps. The frequency of these examinations will vary according to the size and number of polyps and the rate at which new polyps are forming. Your doctor will discuss the schedule of follow up examinations most appropriate for you.
What factors influence the risk of colon polyp recurrence?
The simplest factor is age. People over the age of 50 have an approximately 40–50% chance of developing a colon polyp. Due to this evidence, the American Gastroenterological Association (AGA) and the American Cancer Society recommend that this subset of people be screened for colon polyps. Once a patient who is 50 years or older is found to have a polyp, there are a number of important factors in terms of determining whether they are at high risk. Family history is probably the number one contributing factor.
It is said that approximately half of the patients who have had a colon polyp, which is approximately half of the age 50+ population, will recur with another polyp within 3 years. Of those patients, approximately 10% will recur with an advanced polyp or with multiple polyps. Morphologic/pathologic features such as size—a polyp that is greater than 1 cm in diameter is a bad risk factor—indicate an advanced polyp. Individuals who recur with risky polyps have an elevated risk of developing colon cancer.
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In terms of diet, what can a patient do to reduce recurrence risk?
Patients who are in an elevated risk category of cancer because of a family history should consider some kind of intervention (ie, chemoprevention). For patients that are under the age of 50, diet (higher intake of bran, fruits, and vegetables; taking supplements) and the amount of exercise can certainly influence the risk of developing a colon polyp, and ultimately, colon cancer. However, if a patient already had a polyp or colon cancer, clinical studies performed by our group, along with studies done by Dr. John Baron and Dr. Arthur Schatzkin, suggest that dietary interventions are not effective in reducing the risk of polyp recurrence.
According to Dr. Baron’s group, calcium is one dietary intervention that is associated with a reduced risk of recurrent polyps. The group did a randomized study of dietary calcium and found a 25% reduction in the risk of recurrence. Although calcium may be easily accessible to many patients, it has also been associated with a risk of developing other types of cancer, specifically prostate cancer. Therefore, calcium may not be the best preventative choice for men with recurrent polyps. Furthermore, the magnitude of calcium’s effect in women is such that it does not change recommendations for surveillance colonoscopies or screening that would follow polyp or colon cancer removal.
What is the rate of recurrence? Is the presence of polyps a strong indicator of colon cancer?
The average annual rate of recurrence in patients who are over 50 years of age and who have a polyp but no history of colon cancer is between 10% and 15% per year. After approximately 3 years, the rate is 35–50%, as documented by numerous intervention studies. For patients who have had colon cancer, the rate of polyp recurrence is higher.
Polyps are an intermediate in at least some colon cancers. From a historical perspective, there are significant data that suggest that if polyps are removed, the risk of colon cancer is reduced. In a recent study, Dr. Nancy Baxter and colleagues found that colonoscopies do not predict colorectal cancer-specific death from right-sided polyps. There are several reasons for this observation, including the possibility that right-sided lesions are more biologically aggressive. The size and pathologic features of the polyp—the appearance of cells and the shape of the polyp itself (eg, flat or elongated)—all contribute to the likelihood that those polyps will develop into colon cancer; however, genetics and family history are the main indicators for colon cancer.