Reexamining who's at high risk for colorectal cancer
Colorectal cancer is cancer that starts in either the colon or the rectum.
This form of cancer is the second most prevalent in the United States. For many people, colorectal cancer can be prevented through regular screenings.
Colonoscopies are considered the gold standard of screening tools for colorectal cancer. In a colonoscopy, a tiny camera is guided through the large
intestine to look for cancer or adenomatous polyps (fleshy growths occurring on the lining of the cancer or rectum that can develop into cancer if
untreated), which are often referred to as adenomas. If polyps are found, a scissors can snip off a piece for biopsy, or even the entire growth, to
determine whether cancer is present.
There is general agreement among physicians that colonoscopies save lives, and that beginning at age 50, every American should have a colonoscopy done
every ten years—at least until age 75, when the possible harm from the procedure may outweigh the benefits. According to both VA guidelines and guidelines
set forth by the American College of Physicians (ACP), some people at additional risk for colon cancer should begin having colonoscopies earlier than
50—and have them done more frequently than every ten years.
A new study, however, has reviewed the evidence relating to one of the groups currently considered "high-risk," and concluded that the studies that
physicians relied on to make this classification do not show that people in that group are, in fact, at higher risk of developing colorectal cancer. The
study, titled "Risk for colorectal cancer in persons with a family history of adenomatous polyps: a systematic review," was published in the May 15, 2012,
issue of the Annals of Internal Medicine.i
The physicians conducting the study, Thomas F. Imperiale, MD, and David F. Ransohoff, MD, looked at 12 studies relating to whether first-degree relatives
(parents, children, brothers, and sisters) of people who have had adenomatous polyps removed from their intestines are at increased risk of developing
colon cancer. Based on these studies, ACP and others currently recommend that those whose parents, children, and siblings have had polyps removed should
themselves have their first colonoscopies at age 40, and every five years thereafter. Imperiale and Ransohoff are concerned this recommendation may be
"Most studies that are cited for the risk for colorectal cancer when relatives have adenomas do not address the issue," wrote Imperiale, an investigator at
the VA Health Services Research and Development Center of Excellence on Implementing Evidence-Based Practice in Indianapolis, Ind., and a professor of
medicine at the Indiana University of School of Medicine and at the University's Regenstrief Institute.
Of the 10 studies physicians used to determine whether having first-degree relatives with adenomas increase the risk for colorectal cancer, the researchers
found that none answered the question at all. Instead, they focused on whether patients whose relatives had had adenomas had an increased risk of
developing adenomas themselves—not cancer.
The researchers identified two additional studies that did look at colorectal cancer but had "important methodological limitations," according to the
authors. One of those studies did show that the risk for colorectal cancer in persons who have first-degree relatives with adenomas is greater than the
risk in persons who do not have such relatives. The other study showed that the risk for colorectal cancers or large adenomas (polyps with an area greater
than one centimeter) in persons who have first-degree relatives with large adenomas is greater than the risk for people whose first-degree relatives do not
have either adenomas or colorectal cancer.
"Properly designed studies are needed to measure the risk, and identify the factors that modify it," concludes Imperiale. "Even the two relevant studies
have design problems that affect their validity and generalizability."
According to the American Cancer Society, about 100,000 Americans will develop colon cancer this year, and 40,000 will develop rectal cancer: the lifetime
risk of developing colon cancer is about 1 in 20. More than 50,000 Americans will die of colorectal cancer in 2012, although the death rate from this form
of cancer has been decreasing for the past 20 years.ii
VA has made it a priority to screen its patients aged 50 years or above for colorectal cancer. A 2011 VA research study analyzed the records of more than
36,000 Veterans receiving care from the Department and found that more than 80 percent of those Veterans had received some form of colorectal cancer
VA physicians usually choose from among three types of screening procedures for colorectal cancer. Besides colonoscopy, the other two are:
An annual fecal occult blood test (FOBT), which detects blood that is not visible in a stool sample; and
A flexible sigmoidoscopy examination every five years. This procedure allows physicians to visually inspect the interior walls of the rectum and the
lower part of the colon using a thin, flexible, lighted tube called a sigmoidoscope.
A more recently introduced test, the fecal immunochemical test (FIT), also detects occult blood in stool. The test reduces the number of false positives
that are found in the FOBT test, which can return positive tests when hemorrhoids or infections are present, or even when a patient's diet consists largely
of red meat. According to Imperiale, this new test "may work better than colonoscopy," and VA recently began a clinical trial comparing colonoscopy to FIT
at 45 sites throughout the nation (www.research.va.gov/currents/may12/may12-04.cfm).
Symptoms of colorectal cancer are numerous and non-specific. They include fatigue, weakness, shortness of breath, changes in bowel habits, narrow stools,
diarrhea or constipation, red or dark blood in the stool, unexplained weight loss, abdominal pain, cramps, or bloating. People who experience these
symptoms for any length of time, even a few days, should call their doctors right away to discuss their concerns and arrange for testing.
TF Imperiale and DF Ransohoff, "Risk for colorectal cancer in persons with a family history of adenomatous polyps: a systematic review." Ann Intern
Med, 2012 May 15; 156(10):703-9.
American Cancer Society Website: http://www.cancer.org/Cancer/ColonandRectumCancer/OverviewGuide/colorectal-cancer-overview-key-statistics
MD Long, T Lance, D Robertson, L Kahwati, L Kinsinger, DA Fisher, "Colorectal Cancer Testing in the National Veterans Health Administration," Dig Dis Sci, 2011 Sep 16. (Epub ahead of print.)