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Colorectal Cancer and Colon Polyps
What is colorectal cancer? What are colon polyps?
Colorectal cancer refers to cancer that develops in the colon or rectum. The colon has four sections and the wall of each of these sections has several layers of tissue which can become infected. Colorectal cancer begins in the innermost layer of the colon and/or rectum and can grow through the remaining layers. The more advanced the disease, the deeper the cancer has invaded these layers.
For many people, colorectal cancer develops slowly over several years. In most cases, the cancer begins as a non-cancerous polyp, which can eventually become cancer. Some polyps, such as adenomatous polyps or adenomas, have the potential to become cancerous. Other types of polyps, such as those that are inflammatory, are not considered precancerous, but they can be a sign that someone is more likely to develop a precancerous polyp. In addition, some chronic diseases, such as Crohn’s disease or ulcerative colitis, can cause dysplasia – cells that are not normal, but not yet cancerous, either. The majority of colorectal cancers are adenocarcinomas, or cancers that line the inside layer of the colon and rectal walls.
Cancer of the colon and rectum is the second leading cause of cancer-related death in the United States and the third most common cancer for both men and women. According to the American Cancer Society, it is estimated that 150,000 Americans are diagnosed with colorectal cancer each year, and 57,000 die from the disease. Without undergoing screening or preventive action, approximately 1 in every 17 people in the United States will develop colorectal cancer at some point in their lives.
Fortunately, the survival rate for colorectal cancer continues to increase, due to advanced colorectal cancer screening techniques. These techniques have allowed polyps to be discovered quicker and removed before they develop into cancer. When colorectal cancer is detected in its earliest stages, it is easier to treat and cure. In fact, more than 90% of individuals with colorectal cancer that is confined to the colon or rectum are alive five years after diagnosis.
What are the risk factors?
The majority of patients who develop colorectal cancer have no known risk factors; therefore, prevention and early detection are key in reducing mortality. Persons considered to be at average risk for colorectal cancer do not fit any of the higher risk categories. Specifically, average-risk persons have no symptoms associated with colorectal cancer, no personal history of colorectal cancer or precancerous polyps, no family history of colorectal tumors, no inflammatory bowel disease and no unexplained anemia (low blood count).
However, there are several known risks factors for developing colorectal cancer, including:
Personal History of Precancerous Polyps or Colorectal Cancer – A personal history of precancerous (adenomatous) polyps or colorectal cancer places a person at higher-than-average risk for the development of new tumors of the colon and rectum. Surveillance colonoscopy is therefore recommended by virtually all physicians. The interval between colonoscopies has been the subject of some debate, and no blanket recommendation can be given for all patients. A rational surveillance strategy should take into account the patient’s age, other medical conditions, life expectancy, completeness of prior examinations, pattern of tumor growth and microscopic features of the previously removed tumors. Typically, patients will undergo repeat colonoscopy 1-5 years after their initial colonoscopy.
Additionally, individuals with relatives (a parent, brother/sister, child) who have had colorectal cancer or colorectal polyps have been shown to be at a higher risk for developing the disease.
Family History of Colorectal Cancer or Adenomatous Polyps – A family history of colorectal cancer or precancerous (adenomatous) polyps increases the risk of developing colorectal cancer. In general, a person’s risk is increased when the affected relative is a first degree relative (i.e., parent, brother/sister, child) and when the affected relative is young when diagnosed with a colorectal polyp or cancer. People in this risk group should begin screening for colorectal tumors at age 40, or 10 years earlier than the age at diagnosis of the affected relative, whichever is earliest. Those patients whose first-degree relatives developed colorectal cancer prior to age 50 may be at higher risk, and complete colonic evaluation with colonoscopy should be strongly considered. Patients with a single second degree relative with colorectal cancer, or a relative with polyps diagnosed over the age of 60, may be screened as an average-risk person.
Hereditary Nonpolyposis Colorectal Cancer (HNPCC) – Hereditary nonpolyposis colorectal cancer is an inherited disorder that predisposes patients to the development of colorectal cancer, with up to 75 percent of patients developing the disease by age 65. Many cases of HNPCC are attributed to mutations of genes that code for mismatch repair proteins, which correct mistakes made during DNA replication. Patients with HNPCC are also at high-risk for developing cancers of other organs, especially the ovary and uterus. These tumors frequently occur at a young age.
The ability to conclusively identify gene carriers is not yet fully developed, thus the incidence of colorectal cancer in gene carriers can only be estimated (approximately 90 percent). In addition, some patients in HNPCC families who do not have identifiable germline mismatch repair gene mutations will develop colorectal cancer. For these reasons, the diagnosis of HNPCC in a family remains clinical. The Amsterdam criteria (colorectal cancer in 3 or more family members; 2 generations affected; 1 affected person a first degree relative of another; and 1 cancer diagnosed prior to age 50) are the strictest criteria and have the highest concordance with known mismatch repair gene mutations. These criteria were originally developed for research purposes, to standardize the definition of HNPCC. However, they fail to identify patients who may be affected with HNPCC but do not fit the strict criteria because of unknown or abbreviated family histories, as well as patients with a personal or family history of extracolonic malignancies associated with HNPCC. A recent National Cancer Institute working group acknowledged the shortcomings of the Amsterdam criteria as clinical guidelines and published recommendations to expand the clinical suspicion of HNPCC to a broader range of patients. The International Collaborative Group on Hereditary Non-Polyposis Colorectal Cancer has also proposed similar criteria.
Expert panels recommend that persons who are members of a family fitting clinical criteria for HNPCC undergo colonoscopy at age 20 to 25, and repeat colonoscopy every 1 to 3 years. The short time interval between colonoscopies results from the accelerated polyp to cancer progression thought to occur in HNPCC. Patients and their family members should be referred for genetic counseling. Germline testing for mismatch repair gene mutations can be considered, but because the predictive value of such testing is only about 50 percent, colonoscopy should be performed, regardless.
Familial Adenomatous Polyposis (FAP) – Familial adenomatous polyposis is caused by a defect in the adenomatous polyposis coli gene, which is inherited directly from the affected parent. Offspring of a person with FAP have a 50 percent chance of receiving the mutated gene. A smaller number of patients develop FAP from spontaneous mutations, and have no prior history of the disorder. Patients with FAP develop hundreds of adenomatous (pre-cancerous) polyps as early as puberty, and will ultimately develop colorectal cancer, usually by age 40. Patients with FAP are also prone to develop a variety of other tumors, notably duodenal adenomas and carcinomas, and desmoid tumors. FAP mutations do occur spontaneously, accounting for patients who are diagnosed with the disease without a family history of FAP. “Attenuated” FAP is a rare deviation of the disease, with polyps and cancers developing later in life.
Patients with a family history of FAP should undergo flexible sigmoidoscopy or colonoscopy at puberty, and lower endoscopy should be repeated every 1 to 2 years. Genetic testing should also be considered, especially in large families where genetic analysis might be more cost-effective than repeated endoscopy.
Inflammatory Bowel Disease – Patients with ulcerative colitis and Crohn’s colitis have an increased risk of developing colorectal cancer. This risk begins approximately 7 to 8 years after diagnosis in patients with pancolitis, and 12 to 15 years after diagnosis in patients with limited left-sided colitis.
It is common practice for patients with ulcerative colitis to undergo screening colonoscopy with multiple random biopsies looking for dysplasia every 1 to 2 years, beginning 7 to 8 years after diagnosis in patients with pancolitis and 12 to 15 years after diagnosis in patients with left-sided colitis. If dysplasia or cancer is found, colectomy should be performed. The recommendations for patients with Crohn’s colitis are less well-defined.
Age – Colorectal cancer rates increase in individuals who are age 50 and older. In fact, more than 90% of cases involve individuals age 50 or older.
Ethnicity – It has been shown that individuals of eastern European Jewish descent (Ashkenazi Jews) have a higher rate of colon cancer.
History of polyps or bowel disease – Certain types of polyps (especially those that are large or numerous polyps) can increase the risk of developing colorectal cancer. In addition, individuals with diagnosed ulcerative colitis or Crohn’s disease have an increased risk for developing colorectal cancer.
Diet, lack of exercise and obesity – A high-fat diet and a lack of exercise can increase the risk of developing colorectal cancer. Also, individuals who are very overweight or obese have an increased risk – especially if their weight is carried in their waist rather than in the thighs or hips.
Smoking and alcohol – Smokers are 30 – 40% more likely than non-smokers to die of colorectal cancer. In addition, heavy use of alcohol has been shown to contribute to this type of cancer.
Having diabetes – Individuals with diabetes have a 30 – 40% increased chance of developing colorectal cancer and often have a higher death rate.
Unfortunately, the majority of people diagnosed with colorectal cancer do not have any of the above risk factors. Therefore, ongoing screening is essential to preventing or detecting this disease at its most curable stage.
What causes it?
There is no known exact cause for most colorectal cancers, but there are known risk factors which may increase an individual’s chance of developing a disease.
Evidence is mounting that colorectal cancer can be prevented by detecting and removing precancerous polyps of the colon, before they develop into cancer. In addition, the detection of early-stage cancers reduces mortality from the disease. Both polyps and early-stage cancers are usually asymptomatic (cause no symptoms); cancers that have grown large enough to cause symptoms have a much worse prognosis. This contrast highlights the need for screening in symptom-free persons. Effective treatment of colorectal cancer that has spread to distant organs is difficult, and most patients ultimately succumb to their disease once it has spread. Therefore, effective initial treatment is critical to control the disease.
The American Cancer Society recommends taking the following steps to reduce your risk of developing colorectal cancer:
Get screened – Most people are of average risk for developing colorectal cancer and require screening beginning at age 50 – the age at which the incidence of colorectal cancer increases. The American Cancer Society recommends that average-risk persons should undergo one of the following screening regimens beginning at age 50:
- fecal occult blood testing annually and flexible sigmoidoscopy every five years;
- air contrast barium enema every five to ten years; and
- colonoscopy every ten years.
Individuals age 50 and older, those with a family history of colorectal cancer and those with other risk factors should schedule a colonoscopy every 10 years. Many experts in the field feel that colonoscopy, being the most sensitive and specific test for the detection of polyps and cancer, is the preferred screening method. Payors for Medicare and many private insurance plans will now reimburse for screening colonoscopy in average-risk persons. Screening colonoscopy every 10 years, beginning at age 50, may ultimately prove to be the most cost-effective method of screening average-risk persons for colorectal cancer. Hopefully, future technologic advances will allow for total colonic evaluation with minimal patient discomfort and embarrassment, at reasonable cost.
Eat right – Limiting foods high in fat and eating plenty of fruits, vegetables and whole grain foods improves overall health and helps to prevent many diseases. Some studies also suggest that taking a daily multivitamin that contains folic acid or a calcium supplement can lower an individual’s risk of developing colorectal cancer.
Exercise – Make exercise a part of your daily routine to improve overall health. Strive for at least 30 minutes of physical activity 3-5 days a week.
What are the symptoms?
You should contact your doctor immediately if you experience any of the following symptoms for more than two weeks:
- Change in bowel habits
- Blood in or on the stool that is bright red or very dark
- Stools that are narrower than usual
- Stomach discomfort, such as excess gas, bloating, a feeling of fullness or cramping
- Diarrhea, constipation or a feeling that the bowel does not completely empty
- Unexplained weight loss
- Constant tiredness
- Vomiting
- Sensation of incomplete evacuation
How are colon cancer and colon polyps diagnosed?
Colonoscopy – Colonoscopy can detect polyps and prevent some cancers at their earliest stages of development. During a colonoscopy, a lighted, flexible endoscope is passed into the rectum and the entire colon is examined for polyps. Colonoscopy is the only screening technique that allows the detection and removal of precancerous polyps throughout the colon and rectum, and is the final common pathway for any positive screening test. In addition, it is the most sensitive and specific test for the detection of polyps and cancers. A complete preparation of the bowel, usually with laxatives the night before the examination, is required. Patients typically receive intravenous sedation during colonoscopy and, thus, require a responsible adult to accompany them home after the procedure.
The ability of colonoscopy to reduce colorectal cancer mortality has been demonstrated indirectly through studies showing that detecting and removing polyps reduces the incidence of colorectal cancer and that detecting early cancers lowers the mortality from the disease. Patients who elect to undergo other colorectal screening examinations (such as FOBT, flexible sigmoidoscopy, and barium enema) should realize that any abnormal result of these less invasive tests will ultimately require colonoscopy.
Fecal Occult Blood Testing (FOBT): Prior to this test, patients follow a specific diet and avoid certain medications for several days. The patient obtains a sample of his/her stool, places it on a card and sends it to the doctor’s office, where it is tested for the presence of blood. Samples containing blood should prompt complete evaluation of the colon, usually by colonoscopy.
Limitations: Even when performed correctly, FOBT still fails to detect many tumors of the colon and rectum because it is a relatively insensitive and nonspecific test. The lack of adequate diet and medication restriction prior to the test, potential for trauma to the anal canal during digital rectal examination, and the inability to always obtain stool from the rectum can make the test unreliable. Although frequently performed by well-meaning physicians, random stool examination has never been demonstrated to have benefit in screening for colorectal cancer.
Flexible Sigmoidoscopy: During this test, a lighted, flexible endoscope is passed into the rectum and lower aspect of the colon, usually after an enema preparation.
Limitations: Flexible sigmoidoscopy only examines 1/6-1/3 of the colon and, therefore, it is usually combined with FOBT as a screening test. Although this combined approach may detect more upstream tumors than flexible sigmoidoscopy alone, 15 to 25 percent of patients with normal flexible sigmoidoscopy and negative FOBT will have tumors in the upstream colon at colonoscopy, calling the rationale for this approach into question.
Barium Enema (Lower GI): During a barium enema or lower GI, the colon and rectum are filled with barium contrast through a catheter placed in the rectum and multiple x-ray images are obtained. The quality of the images can be improved by using air in addition to the barium (“air contrast barium enema”). A bowel preparation is required, but patients typically do not receive sedation. Air contrast barium enema will detect 50 to 80 percent of small polyps (< 1 cm), 70 to 90 percent of large polyps (> 1 cm) and 50 to 80 percent of early stage cancers.
Limitations: Single column barium enema is less sensitive than air contrast barium enema and should be combined with flexible sigmoidoscopy if used as a screening tool. Another major limitation of barium enema is that if lesions are detected, patients will usually require colonoscopy, which requires a second complete bowel preparation prior to the procedure.
CT Colography (Virtual Colonoscopy): CT colography involves thin section computed tomography (CT) with three-dimensional computer reconstructions to examine the lining of the colon. This technology was developed in an attempt to increase compliance with colorectal cancer screening, based on the impression that persons would be more inclined to have a “scan” than a “scope.” Although the technique has the advantages of being relatively non-invasive and not requiring sedation, a vigorous oral laxative preparation is required, because stool cannot be differentiated from tumors on CT. In addition, a rectal catheter and air are utilized to stretch the colon. CT colography cannot be assumed to be more appealing to all patients who are reluctant to undergo colonoscopy, because many patients are deterred more by the laxative preparation than by the endoscopic procedure itself, and find rectal air insufflation in the absence of sedation uncomfortable.
Limitations: Initial trials demonstrated that CT colography was not as sensitive as colonoscopy in the detection of small polyps, although with improvements in technology and with greater experience with interpretation, CT colography may prove to be as reliable as colonoscopy in detecting colorectal neoplasia. Regardless of its accuracy, CT colography suffers from the disadvantage that biopsies cannot be obtained and positive findings require patients to undergo colonoscopy.
Who treats this condition?
The technical aspects of surgery for rectal cancer have received considerable attention in recent years because of wide surgeon-to-surgeon variability in both local control of tumor and survival rates following curative resection. The two most commonly identified surgeon-specific factors associated with good outcome have been specialty training and high case volume. The use and timing of adjuvant radiation or chemoradiation treatment has also been shown to be significant, even when combined with optimal surgery.
Surgeons with specialty training and high volume practices have demonstrated better results when treating patients with rectal cancer, which should not be surprising. Recent data from the American Board of Surgery suggests that the average general surgeon in the United States performs only 1-2 proctectomies per year for any reason. This low incidence of practice experience is compounded by the relatively small number of patients with rectal cancer encountered during a general surgical residency. Data from the Residency Review Committee and the American Board of Surgery indicates that the average colorectal surgery resident performs more colectomies and abdominoperineal resections in a single year of training than the average general surgical resident performs in 5 years of residency. It is, therefore, not surprising that the experience of a colorectal surgeon with an interest in rectal cancer will be far greater than the average general surgeon.
Simply stated, the best possible outcomes for patients suffering from colorectal cancer will be achieved by well-trained surgeons, performing a high volume of surgery for colorectal cancer, who are willing to invest the time and effort to build a successful treatment team.
What treatments are available?
Once colorectal cancer has spread to other organs or recurred locally, it is very difficult to cure. Therefore, efforts must be focused on providing the best initial treatment of the disease once it is detected. Patients suffering from rectal cancer are at higher risk for adverse outcomes than patients with colon cancer, and thus much research has been devoted to improving care for these patients.
Chemotherapy, administered by a medical oncologist, is an important adjuvant treatment for some patients with colon cancer, and is usually administered after the patient has recovered from surgery. The decision to undergo chemotherapy is based on the stage of disease, the appearance of the cells on histologic analysis and the overall fitness of the patient.
Radiation therapy is an important adjuvant treatment for many patients with rectal cancer. It is usually administered prior to surgery because it has a greater effect and is less toxic than when it is administered following surgery. Radiation therapy is administered by a radiation oncologist and is often given in combination with chemotherapy.
Coordination of adjuvant treatment should be made between the surgeon, the medical oncologist and the radiation oncologist.
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