Tuesday, December 1, 2009
It is now well established that screening for colon cancer can reduce the number of deaths from the disease. The important distinction between colorectal screening and some other forms of cancer screening, such as mammography, is that colorectal screening is designed to prevent colorectal cancer by identifying and removing benign polyps, which are potentially pre-cancerous, before the cancer starts. This is a significant difference from the more widely accepted mammography screening for breast cancer, which attempts to identify cancer in an early stage, but does not have the ability to prevent cancer.
Although there are various methods of screening for colon cancer, there is a wide consensus that colonoscopy is the preferred screening method. Colonoscopy can detect small growths known as polyps before they become cancerous. These polyps can be removed during the procedure, without surgery, thus preventing the cancer from ever having the chance to develop. Colonoscopy can also detect cancers early before symptoms arise. Cancers detected at an earlier stage have a much higher cure rate than those that are detected at a later stage.
Colorectal Cancer
Colorectal cancer is cancer of the large intestine. The large intestine is composed of the colon and the rectum. The average large intestine is about six-and-a-half feet long, with the rectum comprising the last six inches of the large intestine. According to the American Cancer Society (ACS), approximately 148,000 people in the United States will have been diagnosed with a new case of colorectal cancer in 2009, making it the fourth most common cancer (not including skin cancer) after lung, prostate, and breast cancer. The average-risk American has about a one in 20 chance of developing colorectal cancer during his or her lifetime. The risk of developing the disease rises with age; 91 percent of colorectal cases occur in individuals aged 50 and older. However, people with family history of the disease may have a much higher risk and thus may require early and more intense screening. Colorectal cancer affects men and women in approximately equal numbers.
The ACS reports that the number of people diagnosed with colorectal cancer has declined over the past two decades, with the decline in cases accelerating to a statistically significant degree from 1998 to 2005. Experts attribute this decrease in part to the increase in screening that allows for the detection and removal of benign colorectal polyps, which are also known as adenomas. Most cancers of the colon or rectum arise from adenomas. There has been a related decrease in the number of deaths from colorectal cancer over the past 20 years in the US, although the estimated 50,000 deaths that will occur from the disease in 2009 still account for about 9 percent of all cancer deaths in the country, and colorectal cancer remains second only to lung cancer as a cause of cancer death.
“It is a tragedy that colorectal cancer, the number two cause of cancer death, is largely preventable, and we are not preventing it because we are not getting enough people into screening,” says Memorial Sloan-Kettering medical oncologist Leonard Saltz, who is a member of the Gastrointestinal Oncology Service.
Screening Options
There are a number of screening procedures that may be used to look for precancerous polyps, such as fecal occult blood test, flexible sigmoidoscopy, and virtual colonoscopy, but standard colonoscopy is recommended in most cases because it allows the doctor to examine the whole colon and to remove or biopsy any suspicious growths.
In a colonoscopy, a doctor uses a thin, flexible tube with a light and camera at its end, known as a colonoscope, to inspect the rectum and the entire length of the colon. Prior to a colonoscopy, the patient undergoes a bowel cleansing to assure a clear view. Patients are usually sedated during the procedure, which generally takes about 30 minutes. Any polyps or other growths that are found during the examination are usually removed or biopsied at the time and sent to a laboratory for examination.
Virtual colonoscopy is a relatively new technique that uses CT scans and a high-powered computer to create a 3-D image that can be used to evaluate a patient’s colon without sedation or the insertion of a colonoscope. However, the same bowel cleansing process used in a standard colonoscopy is required. Also, the air that is pumped into the colon to provide better viewing can be uncomfortable. If any suspicious growths are detected, a standard colonoscopy is usually required.
Colonoscopy: The Gold Standard of Colorectal Cancer Screening
According to the ACS, approximately 14 million colonoscopies are performed in the US each year, with only about 50 percent of Americans over the age of 50 receiving the recommended screening.
In 1993, Memorial Sloan-Kettering gastroenterologist Sidney Winawer led a study [PubMed Abstract], known as the National Polyp Study, which supported the long-suspected concept that colon cancer arises from benign polyps, and that removing these polyps during colonoscopy would interrupt the cancer-development process. Other studies have since supported the findings. Colonoscopy became the preferred method of colorectal screening, recommended by the ACS and the American Gastroenterological Association.
Not all doctors performing colonoscopies are equally skilled in terms of their ability to detect polyps. In 2006, a study [PubMed Abstract] published in the New England Journal of Medicine found that the skill and thoroughness of the doctor performing the colonoscopy are important for the maximal success of the procedure. In particular, the study found that the length of time the doctor spends on withdrawing the scope and examining the colon are related to the number of polyps that are removed. As a result, experts recommend that individuals ask their gastroenterologists about their general experience with colonoscopy and, in particular, about their detection rate for finding polyps during the colonoscopies they have performed.
Another crucial factor for the success of colonoscopy is the quality of bowel preparation. A clean colon allows the physician to see and detect lesions.
In general, it is recommended that you speak with your doctor about your family history of colorectal cancer, including a discussion of appropriate screening recommendations to lower your risk of developing the disease.
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