Screening can reduce colorectal cancer mortality, as well as the incidence of the disease, but it is has been unclear which screening method is the best.
Two long-term studies confirm the effectiveness of major screening technologies, but leave the question of superiority up in the air. Both appear in the September 19 issue of the New England of Medicine.
In one study with a 22-year follow-up period, colonoscopy was shown to have advantages over sigmoidoscopy for the prevention of colorectal cancer. In addition, screening colonoscopy reduced the risk for any colorectal-cancer-associated death, whereas sigmoidoscopy lowered the risk of dying only from left-side tumors.
"Our data support the use of colonoscopy as a the preferred screening option for patients if the primary consideration is maximal reduction in risk of colorectal cancer," said study coauthor Andrew Chan, MD, MPH, associate professor of medicine, gastroenterology, at the Massachusetts General Hospital in Boston.
In the second study, which has a 30-year follow-up period, annual and biennial screening with fecal occult blood testing reduced the risk for death from colorectal cancer. The risk for death from colorectal cancer was 32% lower with annual screening, compared with no screening, and 22% lower with biennial screening.
The Best Method?
But how does colonoscopy compare to fecal occult blood screening?
Both of these tests are effective for colorectal cancer screening, and both these studies support current screening guidelines, according to an accompanying editorial by Theodore R. Levin, MD, and Douglas A. Corley, MD, PhD, from Kaiser Permanente Medical Centers in California.
In addition, the screening tests have improved since the trial participants first used them.
The editorialists emphasize that these studies are quite different from one another, which makes it difficult to make direct comparisons of effectiveness.
"It would be tempting to use these 2 studies to draw conclusions about which test is more effective," they write.
The reduction in mortality was better with colonoscopy than with annual fecal occult blood testing (68% vs 32%). However, it is a mistake to directly compare these results, the editorialists point out. "The 2 study populations are not comparable: one was a randomized trial, the other an observational study of volunteers, and both tests have undergone improvements since the studies were performed."
To date, no completed studies directly compare fecal occult blood testing with colonoscopy, although randomized trials are ongoing.
Although the performance of colonoscopy has probably improved because of the greater recognition of nonpolypoid colorectal neoplasia, and it "appears to have a performance edge over the old guaiac fecal occult blood test, fecal occult blood testing has largely been replaced by the more effective fecal immunochemical test (FIT)," they note. This newer test has better sensitivity than the guaiac fecal occult blood testing used in that study.
Of importance, recent data show that individuals were more likely to "complete screening if they were offered guaiac fecal occult blood tests, a choice between colonoscopy and guaiac fecal occult blood tests, or FIT alone, as compared with being offered colonoscopy alone," they write.
In the Kaiser Permanente Northern California health system, where both editorialists practice, a combined approach is used, and substantial improvement in rates of colorectal cancer screening has been achieved.
Colonoscopy vs Sigmoidoscopy
In the first study, Dr. Chan and colleagues evaluated the association between the use of lower endoscopy (updated biennially from 1988 to 2008) and colorectal cancer incidence (to June 2010) and mortality (to June 2012). The cohort involved 88,902 individuals who participated in the Nurses' Health Study and the Health Professionals Follow-up Study.
Over a follow-up period of 22 years, there were 1815 documented cases of colorectal cancers and 474 colorectal-cancer-specific deaths.
When endoscopy screening was compared with no screening, multivariate hazard ratios (HRs) for colorectal cancer were 0.57 after polypectomy, 0.60 after negative sigmoidoscopy, and 0.44 after negative colonoscopy.
A negative colonoscopy was associated with a reduced incidence of proximal colon cancer (multivariate HR, 0.73), and the rate of mortality from proximal colon cancer was lower after screening colonoscopy (multivariate HR, 0.47), but not after sigmoidoscopy.
The multivariate HRs for colorectal cancer mortality were 0.59 after screening sigmoidoscopy and 0.32 after screening colonoscopy.
Even though colonoscopy appears to have some advantages over sigmoidoscopy, there are reasons patients might opt for the latter. "A screening sigmoidoscopy generally does not require a full bowel preparation or the administration of sedation, so patients undergoing the procedure can generally expect to miss less work," Dr. Chan told Medscape Medical News.
"In addition, although serious complications from both colonoscopy and sigmoidoscopy are quite rare — generally about 1 to 3 per 1000 patients — they do occur at a higher rate with colonoscopy than with sigmoidoscopy," he noted.
Dr. Chan and colleagues point out that although randomized controlled trials have shown that screening with flexible sigmoidoscopy reduces the incidence of colorectal cancer and associated mortality, comparable data for screening colonoscopy are not yet available.
"I think that, based on the data assembled so far and the widespread availability of colonoscopy, we should continue our current practice of recommending colonoscopy as one of a few screening options, with a full discussion of the risks, benefits, and areas of uncertainty associated with each test," said Dr. Chan.
Reduces Long-term Risk
In the second study, Aasma Shaukat, MD, MPH, from the University of Minnesota in Minneapolis, and colleagues provide an update to the Minnesota Colon Cancer Control Study, which assessed the long-term effect of fecal occult blood test screening on all-cause and colorectal cancer mortality.
The initial cohort involved 46,551 participants 50 to 80 years of age who were randomized to usual care or to annual or biennial screening with fecal occult blood testing. Screening tests were performed from 1976 to 1982 and from 1986 to 1992.
The researchers used the National Death Index to obtain updated information about the participants and to determine cause of death.
A total of 33,020 participants (70.9%) died from any cause during the 30-year follow-up period; 732 of the deaths were attributable to colorectal cancer.
Table. Deaths From Colorectal Cancer in the Study Groups
| Deaths | Annual Screening (n = 11,072) | Biennial Screening (n = 11,004) | Usual Care (n = 10,944) |
| n (%) | 200 (1.8%) | 237 (2.2%) | 295 (2.7%) |
Annual screening lowered colorectal cancer mortality (relative risk [RR], 0.68), as did biennial screening (RR, 0.78). There was no reduction in all-cause mortality with annual screening (RR, 1.00) or with biennial screening (RR, 0.99).
Men 60 to 69 years of age got the most benefit from screening. RR for death from colorectal cancer was 0.46 with annual screening, 0.42 with biennial screening, and 0.44 for either screening.
The overall reduction in colorectal cancer death associated with biennial screening was greater for men than women (P = .04 for interaction). This difference was not observed with annual screening (P = .30 for interaction) or with the 2 screening methods combined (P = .06 for interaction).
"The reductions in colorectal cancer mortality in the Minnesota Colon Cancer Control Study are comparable to those reported in randomized clinical trials of screening with flexible sigmoidoscopy, suggesting that fecal occult blood testing remains an effective and acceptable method of screening," the authors write. "Stool-based tests for colorectal cancer screening are an active area of current research, with development and testing of new stool-based tests."
The study by Dr. Chan and colleagues was supported by grants from the NIH, the Bennett Family Foundation, and the Entertainment Industry Foundation through the National Colorectal Cancer Research Alliance. Some of the investigators received outside support, as detailed in the paper. Dr. Chan reports receiving consulting fees from Bayer Healthcare, Pfizer, Millennium Pharmaceuticals, and Pozen. The study by Dr. Shaukat and colleagues was supported by a grant from the Veterans Affairs Merit Review Award Program and research contracts from the National Institutes of Health and the National Cancer Institute. Dr. Levin reports unpaid research collaboration with Exact Sciences.
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