How prevalent is colorectal cancer (CRC)?
CRC is a common and lethal disease. In the United States, CRC is the third most commonly diagnosed cancer and the second leading cause of cancer death. Approximately 148,610 new cases of CRC are diagnosed each year in the United States, of which 106,680 are colon and the remainder rectal cancers. Globally, the incidence of CRC varies ten-fold, with the highest incidence rates in North America, Australia and northern and western Europe.
What are the risk factors?
Environmental and genetic factors can increase the likelihood of developing CRC. Consider the following, all of which elevate an individual's risk of developing CRC:
- Specific genetic disorders such as familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer.
- Personal history of sporadic cancers or adenomatous polyps, which increases the risk of large bowel cancer.
- Family history of colorectal cancer in a first-degree relative (parent, sibling or child), which increases an individual's risk by 1.7 percent. The risk is further increased if two first-degree relatives have colon cancer or if the index case is diagnosed before 55 years of age.
- A family history of colonic adenoma, which appears to carry the same significance as a family history of CRC.
- Inflammatory bowel disease (IBD), such as ulcerative colitis and Crohn's colitis.
- Diabetes mellitus, insulin resistance and chronic insulin therapy.
- Alcohol consumption increases risk modestly, particularly in those who consume alcohol in excess of 45 grams per day.
- Cigarette smoking.
- Ureterocolic anastomoses.
- Prior pelvic irradiation.
- Consumption of red or processed meats.
Can colorectal cancer be prevented? How?
Screenings can detect CRC when it can be treated. In the meantime, certain practices have been identified as protecting the body against CRC, including:
- Diet high in fruits and vegetables, and low in red meat, animal fat and/or cholesterol.
- Folic acid, vitamin B6 and calcium.
- Regular physical activity and maintenance of normal body weight.
- Smoking cessation.
- Regular use of aspirin or nonsteroidal anti-inflammatory drugs.
- Hormone replacement therapy in postmenopausal women, although these drugs are not routinely recommended for chemoprevention of colon cancer due to the associated long-term risks.
- HMG-CoA reductase inhibitors (statins), although data is conflicting.
Are there symptoms to the disease?
Symptoms vary depending on the location of the cancer within the colon or rectum, though there may be no symptoms at all. The most common presenting symptom is rectal bleeding. Cancers arising from the left side of the colon generally cause bleeding, and in their late stages may cause constipation, abdominal pain and obstructive symptoms. On the other hand, right-sided colon cancer may produce vague abdominal aching or weakness, weight loss and anemia from chronic blood loss.
Does it affect women more than men? Caucasians more than other ethnic groups?
Men tend to get colorectal cancer at an earlier age than women, but women live longer so they 'catch up' with men and, thus, the total number of cases in men and women is equal. In the United States, incidence rates of colon cancer declined by 3 percent between 1998 and 2000. During the period from 1996 to 2000, the average annual incidence rates per 100,000 population were 64.2 from men and 46.7 for women. Despite such data, during the same time period, the incidence rates for right-sided cancer increased, particularly in women. In addition, while tobacco and alcohol increase the risk of colorectal cancer, women who smoke are a higher risk. Among women, CRC screening rates are still relatively low (30-40%) and are comparable to mammography rates 20 years ago. African Americans are at a much higher risk for colon cancer than other races. They have a significantly lower age at diagnosis and experience a larger number of polyps and cancer in the proximal colon. Their survival is reduced compared to Caucasians.
Does age play a role in incidences of colorectal cancer?
Age is a major risk factor for sporadic CRC. The lifetime incidence of CRC in patients at average risk is about 5 percent, with 90 percent of cases occurring after the age of 50.
Is colorectal cancer always fatal? What are the mortality rates?
Most colon and rectal cancers originate from benign wart-like growths on the inner lining of the colon or rectum called polyps. Not all polyps have the potential to transform into cancer. Those that do are called adenomas. It takes more than 10 years in most cases for an adenoma to develop into cancer. Screening identifies cancers earlier, before symptoms develop, which dramatically improves the chance of survival. Identifying and removing polyps before they become cancerous actually prevents the development of colorectal cancer. The pathologic stage at diagnosis remains the best indicator of long-term prognosis. The most important characteristics are the presence of distant metastases, local tumor extent, nodal positivity and residual disease. Five-year survival rates vary from 93 percent for stage I to 8 percent for stage IV colon cancer. Five-year survival rates for rectal cancer tend to be somewhat lower.
What sorts of screenings are available?
The American College of Gastroenterology considers colonoscopy the preferred screening test, but the following tests are available:
- Annual fecal occult blood test. If this comes back positive, a colonoscopy should be done.
- Double contrast barium enema. It is less effective than colonoscopy and due to its limitations, not widely used for CRC screening.
- Sigmoidoscopy for examination of the lower colon and rectum. If an adenoma is found, a colonoscopy should be performed. Sigmoidoscopy does not examine the entire colon and so is less reliable. Sedation is usually not used. It is performed every five years, often in conjunction with an annual fecal occult blood test.
- Colonoscopy. The entire colon and rectum is examined and polyps can be removed during the procedure, which is usually done under sedation.
- Computed tomographic (CT) colonography and magnetic resonance (MR) colonography, sometimes called "virtual colonoscopy." Both are fairly new methods and not yet established as reliable screening methods. If polyps are found, a colonoscopy with polypectomy should be performed.
Who should be screened? How often?
Screenings can detect CRC when it can be treated. For individuals at normal risk, screening tests should begin at age 50. The preferred approach is a screening colonoscopy conducted every 10 years. In addition, consider the following recommendations for screening:
- Physician experts with the American College of Gastroenterology issued new recommendations that CRC screening in African Americans begin at age 45.
- Colonoscopic surveillance needs to be performed at more frequent intervals for individuals at high risk for colon cancer (for instance, those with a personal history of CRC or adenomatous polyps, family history of CRC, HNPCC, FAP or IBD).
- An alternate strategy consists of annual stool test for blood and a flexible sigmoidoscopic exam every three to five years.
Does screening hurt?
Screening colonoscopy is done under conscious sedation using a combination of painkiller and sedative given intravenously. Patients are usually comfortable during and after the colonoscopy. The day before the procedure, the patients need to take a bowel preparation, which is available in different forms and well tolerated. Complications including perforation and major bleeding are unusual, about one to two per 1,000 procedures.