Worth of Sigmoidoscopy Screening for Colon Cancer Still Uncertain
Some reduction in mortality rates found, but experts say more follow-up needed
MONDAY, June 1 (HealthDay News) -- Patients checked for colon cancer with a procedure called flexible sigmoidoscopy showed no significant reduction in risk over seven years, but the screening did seem to lower the risk of dying from the disease, Norwegian researchers report.
There are several methods available for colon cancer screening including colonoscopy, which involves a look at the whole colon and the removal of any precancerous or cancerous polyps. In addition, there is flexible sigmoidoscopy, which uses a flexible endoscope to examine the large intestine only. There are also noninvasive tests such as fecal occult blood sampling and CT colonoscopy.
"Flexible sigmoidoscopy screening looks promising, but the effect on a population level appears less than expected and further follow-up is required," said lead researcher Dr. Geir Hoff, from the Cancer Registry of Norway in Oslo.
These are the first results from the trial, and it may be that seven years is too short a time to see the true effect of screening, Hoff said.
"The results suggest that flexible sigmoidoscopy screening may be a very efficient way of screening with an aim of reducing mortality and the risk of getting colorectal cancer, but the effect may be less than anticipated and certainly occurs later than expected in the follow-up period," Hoff added.
Until now, there have been results from randomized trials only for one colorectal cancer screening modality -- screening for blood in the stools, Hoff said. "Still, colonoscopy is recommended in several European countries and the U.S.," he added.
The report is published in the June 1 online edition of the BMJ, to coincide with the scheduled presentation of the findings Monday at the Digestive Diseases Week meeting in Chicago.
For the study, Hoff's team randomly assigned almost 56,000 men and women, aged 55 to 64, to be invited to screening for colon cancer with flexible sigmoidoscopy, while the others were not invited. The researchers followed all the participants for an average of seven years.
Hoff's group found no significant difference between the two groups in the number of those who developed colon cancer. Among those in the group that was invited to get screened, death from colon cancer was reduced by 27 percent compared with those who were not screened, but that percentage was not statistically significant, the researchers noted.
However, for those who actually underwent screening, death from colon cancer was reduced by 59 percent compared with people in the non-screening group. Moreover, for cancers that could have been found by flexible sigmoidoscopy, death from colon cancer was reduced by 76 percent, the team noted.
Both reductions in mortality are significant, the researchers say. But according to Hoff, the drop in deaths might also be due to what researchers call "self-selection bias": Heath-conscious people may be the ones choosing to get screened.
"A major reason for non-compliance to screening is that people are not convinced that there is 'anything in it for them,'" Hoff said. "Being able to quantify an effect to present potential screening participants requires randomized trials like this one. The study illustrates the need for randomized population screening trials before recommending widespread use of screening."
Dr. Thomas Imperiale, a professor of medicine at Indiana University Medical Center in Indianapolis and author of an accompanying journal editorial, noted that seven years was still too short a time to see a reduction in colon cancer from screening. And he advises everyone that it's better to get screened than not.
"These are early results. They show some promising findings," Imperiale said, but "we would not yet expect to see a reduction in colorectal cancer."
"There are options, which is good," Imperiale said. "The bottom line is that people should do something. What they do depends on their preferences and their risk, but they should do something -- do a test."
Another expert, Dr. Durado Brooks, director of colon and prostate cancer prevention programs at the American Cancer Society, agreed that seven years may be too short a follow-up.
In the study, there was a trend toward fewer incidence of cancer after screening, Brooks, said. "One of the questions is, is seven years too short a window? If they look at this again in another four or five years will the difference be statistically significant?"
Brooks noted that some countries have started mass colon cancer screening programs using flexible sigmoidoscopy, "because it is lot more available and less expensive than trying to screen everyone with colonoscopy. Flexible sigmoidoscopy is one of the methods recommended for screening by all of the major organizations."
For more information on colon cancer, visit the American Cancer Society.