Colorectal cancer is a cancer of the large bowel [colon] or rectum. These cancers are common and deadly; approximately one-third of people who develop it die, making it the second leading cause of cancer death. However, screening tests make it possible to detect existing cancers at an early, treatable stage, before there are any symptoms and prevent the development of colorectal cancer by identifying and removing early growths called adenomatous polyps.
All adults should undergo screening beginning at age 50 or earlier, depending upon a person’s risk of developing colorectal cancer. A history of colon cancer in the family, especially if a parent or sibling increases the risk.
Video Blog: Colonoscopy and Colon Cancer Screening
IMPORTANCE OF SCREENING
Most colorectal cancers develop slowly over many years. They begin as small, benign tumors called adenomatous polyps. These polyps grow, develop precancerous changes, eventually become cancerous, and later spread and become incurable. This progression usually takes about 10 years in most people.
Colon cancer screening tests work by detecting precancerous polyps or cancer while it is still curable. Regular screening for and removal of polyps can very significantly reduce a person’s risk of developing colorectal cancer.
WHO SHOULD BE SCREENED?
Everyone should be screened. Several factors increase an individual’s risk of developing colorectal cancer. Having one or more of these factors will determine the age at which screening should begin, the frequency of screening, and the screening tests that are most appropriate.
RISK FACTORS FOR COLON CANCER
Several characteristics increase the risk of colorectal cancer two to several fold. While each individual risk factor adds some risk, risk is substantially increased if several are present together.
- Family history of colorectal cancer – Having colorectal cancer in a family member increases the risk of getting the cancer, especially if it is a first degree relative (a parent, brother or sister, or child), if several family members are affected, or if the cancers have occurred at an early age (eg, before age 50 years).
- Prior colorectal cancer or polyps – People who have previously had colorectal cancer have an increased risk of developing a new colorectal cancer. People who have had adenomatous polyps are also at increased risk for developing colorectal cancer.
- Increasing age – Although the average person has a 5 percent lifetime risk of developing colorectal cancer, 90 percent of these cancers occur in people older than 50 years of age. Risk increases with age throughout life.
- Race – African Americans have a higher risk of dying from colorectal cancer than white Americans. This risk is high in native Alaskans and low in American Indians.
- Lifestyle factors – Several lifestyle factors increase the risk of colorectal cancer, including: A diet high in fat and red meat and low in fiber, Eating charred meats, A sedentary lifestyle, Cigarette smoking, Genetic conditions (see below).
- Familial adenomatous polyposis (FAP) is an uncommon inherited condition that increases a person’s risk of colorectal cancer. Nearly 100 percent of people with this condition will develop colorectal cancer during their lifetime, and most of these cancers occur before the age of 50 years. FAP causes hundreds of polyps to develop throughout the colon.
- Hereditary nonpolyposis colon cancer (HNPCC) is another inherited condition associated with an increased risk of colorectal cancer. It is slightly more common than FAP, but is still uncommon, accounting for about 1 in 20 cases of colorectal cancer. About 70 percent of people with HNPCC will experience colorectal cancer by the age of 65. Cancer also tends to occur at younger ages and in the part of the colon on the right side of the body (the ascending colon). HNPCC is suspected in those with a strong family history of colon cancer; several family members from different generations may have been affected, some of whom developed the cancer relatively early in life. Persons with HNPCC are also at risk for other types of cancer, including cancer of the uterus, stomach, bladder, kidney, and ovary.
- Inflammatory Bowel Disease – People with Crohn’s disease of the colon or ulcerative colitis have an increased risk of colorectal cancer. The amount of increased risk depends upon the amount of inflamed colon and the duration of disease. Risk is not increased in people with irritable bowel syndrome.
FACTORS THAT MAY DECREASE THE RISK OF COLON CANCER
- Eat and overall healthy diet that is high in fiber and low in red meat.
- When cooking meat, do not burn or blacken it (charring can create carcinogens)
- Calcium 800-1200mg per day
- Don’t drink more than 2 alcoholic beverages daily
- Don’t smoke
- Get regular exercise and maintain body weight that is not overweight
- Aspirin, ibuprofen, and related nonsteroidal antiinflammatory medications may decrease the risk of developing colorectal cancer but they can also cause problems such as ulcers and bleeding. There is not enough evidence to recommend aspirin or NSAIDs as a preventive treatment for colon cancer
- Antioxidants such as vitamin E, selenium, and beta carotene have not shown risk reduction
- Unfortunately, no special diet or life style modification or supplement can reliably reduce the risk of colon cancer. These measures thus do not replace colonoscopy as the primary and most effective preventative technique.
Fecal occult blood test
Colorectal cancers and polyps can bleed, releasing visible or microscopic amounts of blood into the stool. The blood is frequently not visible to the naked eye, requiring specialized tests for chemical detection. The fecal occult blood test can be used to detect blood in the stool. This simple test is performed by putting small amounts of stool on chemically coated cards or into a chemical solution. One or more samples from one or several bowel movements are obtained at home and returned to the office for analysis.
Risks and disadvantages Because polyps seldom bleed, the fecal occult blood test is less likely to detect polyps than other screening tests. In addition, only 2 to 5 percent of people with a positive test actually have colorectal cancer and approximately half of patients who do have colon cancer have a negative test for occult blood in the stool. If a fecal occult blood test has a positive result, the entire colon should be examined, usually with colonoscopy.
Sigmoidoscopy allows direct viewing of the lining of the rectum and the lower part of the colon. Due to the lack of visualizing the entire colon and thus not detecting lesions above the reach of the sigmoidoscope, this test is not usually recommended as a screening tool for colon cancer.
Fecal occult blood test and sigmoidoscopy
Combined screening with a fecal occult blood test and sigmoidoscopy may be more effective than screening with either test alone.
Colonoscopy is the “gold standard” screening test for colorectal cancer. It allows a physician to see the lining of the rectum and the entire colon. After taking bowel cleansing laxatives, the patient is given a mild sedative drug and a thin, flexible lighted tube is used to directly view the lining of the rectum and the entire colon. Polyps and some cancers can be removed during this procedure. Colonoscopy detects most small polyps and almost all large polyps and cancers. The risks of colonoscopy are small. Colonoscopy can lead to serious bleeding or a tear of the intestinal wall in about 1 in 1,000 people. Although an excellent test, colonoscopy can miss polyps and cancer, especially when located behind folds in the colon and not well in view during the exam. Because the procedure requires sedation, the person must be accompanied home after the procedure and the person should not return to work or other activities on the same day.
A computed tomography (CT) scan is performed after taking a bowel cleansing similar to colonoscopy. This test can detect polyps and cancer with reasonably good accuracy. It does expose the patient to a dose of radiation and can not biopsy or remove any suspicious lesions. Medicare and most insurance companies have not authorized payment for virtual colonscopy as a screening test.
FREQUENCY AND TIMING OF SCREENING COLONOSCOPY
The screening plan that is recommended depends upon a person’s risk of colorectal cancer.
Timing of screening for those with an average risk of colorectal cancer
People with an average risk of colorectal cancer do not have close relatives with colorectal cancer (see below) or precancerous polyps nor do they have other risk factors mentioned above. They should begin screening at age 50.
Timing of screening for those with an increased risk of colorectal cancer
Screening plans for people with an increased risk may entail screening at a younger age and more frequent screening.
– People who have one first-degree relative (parent, brother, sister, or child) with colorectal cancer or adenomatous polyps at a young age (before the age of 60 years), or two first-degree relatives diagnosed at any age, should begin screening for colon cancer earlier, typically at age 40, or 10 years younger than the earliest diagnosis in their family, whichever comes first. Screening usually includes colonoscopy, which should be repeated every five years.
– People who have one first-degree relative (parent, brother, sister, or child) who has experienced colorectal cancer or adenomatous polyps at age 60 or later, or two or more second degree relatives (grandparent, aunt, uncle) with colorectal cancer should begin screening at age 40, and screening should be repeated as for average risk people.
– People with a second-degree relative (grandparent, aunt, or uncle) or third-degree relative (great-grandparent or cousin) with colorectal cancer are considered to have an average risk of colorectal cancer and begin screening at age 50.
– In people with ulcerative colitis or Crohn’s disease of the colon, the optimal screening plan depends upon the amount of colon affected and the duration of the disease. Screening usually entails colonoscopy once every one to two years beginning after eight years of inflammation of the entire colon or after 15 years of colitis of the sigmoid colon and rectum.