Screening for Colorectal cancers is done to detect
two types of lesions: Cancerous lesions and polyps which might prove to be
cancerous or later turn cancerous.
The non-invasive tests for the detection of
colorectal cancer include the Fecal Immunochemical testing (FIT), fecal occult blood
testing (FOBT) and stool DNA testing. The more invasive screening tests include
colonoscopy, sigmoidoscopy and barium enema.
The fecal immune-chemical testing (FIT) is a
non-invasive test which includes an at-home collection of stool samples, which
are then lab tested mainly for detection of the presence of any blood in the
feces. Blood in the feces is not always visible with naked eyes and is thus
tested chemically. The presence of blood may be suggestive of a cancerous
lesion in the colorectal area. However, feces can test positive for blood even
due to other causes such as gastrointestinal bleeding, ulcers, adverse drug
reaction, use of NSAIDS etc.
Colonoscopy is an invasive method of detection where
a long tube with a small camera at the end is inserted through the anus into
the colon and the areas of colon are viewed on the screen. The procedure
usually is done with the help of sedatives in order to reduce the discomfort to
the patient. Areas of abnormal growth in the colon can be removed for testing
during this procedure. A more clear and elaborate view of small and big
cancerous growths is obtained with this procedure.
A positive outcome of fecal-immunochemical testing
(FIT) usually calls for a detailed testing with colonoscopy. This is done with
the aim to precisely detect the presence of colorectal cancer (if any) and the
extent of its spread. A recent study compared colonoscopy with FIT in the
screening of colorectal cancer amongst the average-risk population.
Published in the New England Journal of Medicine,
the study was conducted on adults between the age group of 50-69 years who were
free of any symptoms of colorectal cancer. A comparison was made between 26,703
adults screened once for colorectal cancer using colonoscopy with 26,599 adults
who were screened using FIT every two years.
The incidence of colorectal cancer was found similar
in both the study groups. But the researchers observed a higher rate of
participation amongst the group tested using FIT. It was noted that advanced
adenomas were detected in more than twice the number of patients undergoing
colonoscopy than the group screened using FIT. Non-advanced lesions were found
four times more commonly in the colonoscopy group compared to the FIT group.
The researchers of the study concluded that a higher participation rate
was seen amongst the group undergoing FIT. Though the number of cases of
colorectal cancer detected was similar in both the groups, a higher number of
adenomas were found in the group undergoing colonoscopy.
In another independent study conducted in Netherlands,
FIT was found to be a more cost-effective method than FOBT for the detection of
colorectal cancer. But a higher haemoglobin cut-off level was recommended for
patients undergoing FIT when the capacity to perform colonoscopy is limited. It
was also recommended that a colonoscopy should be performed in all cases
detected with adenomas.