Immunochromatographic Test Superior to Gold Standard for Colorectal
Cancer Screening


Alison Palkhivala
Medscape Medical News 2005. © 2005 Medscape




Sept. 14, 2005 (Montreal) — A new immunochromatographic fecal occult
blood test (IOBT) is far more sensitive than the standard guaiac-
based fecal blood test (GOBT) for detecting colorectal cancer as well
as precancerous states, according to a head-to-head comparison.

"This immunochemical test should be considered the first-choice fecal
occult blood test for screening for colorectal cancer in the average-
risk population," presenter Enrique Quintero, MD, told Medscape. He
is chief of the gastroenterology department at the Hospital
Universitario des Canarias, La Laguna, Tenerife, Spain.

Dr. Quintero and colleagues compared the IOBT, which was developed in
Japan and is called OC-Light, directly with the current standard GOBT
(Hemo-Fec). Their goal was to determine which test had the most
sensitivity and specificity for detecting colorectal cancer and
precancerous states compared with colonoscopy. He presented their
findings in a poster here at the annual meeting of the World Congress
of Gastroenterology.

"It's very easy to take a sample [using the IOBT]," said Dr.
Quintero. "You collect the sample in a little bottle and put a strip
inside. If you get one blue band, the test is negative, if you get a
second [blue] band, that means the test is positive." In Europe, the
test costs about 3.00 Euros.

Between July 2003 and April 2005, the investigators randomly selected
2,650 individuals aged 50 to 75 years from the Social Security
Register of the Canary Islands for participation in the study. They
excluded all those with regular use of nonsteroidal anti-inflammatory
drugs or anticoagulants, recent history of screening for colorectal
cancer or digestive tract bleeding, and a family or personal history
of colorectal cancer, inflammatory bowel disease, or coagulopathy.
The remaining 2,020 participants, considered to represent a
population at average risk for colorectal cancer, were asked to take
the GOBT and IOBT and were also invited to undergo a colonoscopy. Of
these patients, 1,559 (77%) completed both fecal occult blood tests.

Overall, 8.4% of patients had positive IOBT test results and 3.8% had
positive GOBT test results. An additional 1.9% of patients had
positive results on both tests. Colonoscopy was performed in 154 of
the 161 patients who had positive results on either of these tests
and on 222 of the 1,398 patients who were negative for both tests.

Of the patients with a positive fecal occult blood test, 26% were
found upon colonoscopy to have advanced adenoma, and 9% were found to
have colorectal cancer. In contrast, of patients with a negative
fecal occult blood test, 2% had advanced adenoma, and none had
colorectal cancer. Of the 14 patients with colorectal cancer, six had
early-stage disease.

The IOBT test was far more sensitive than the GOBT test, with a
sensitivity of 50% for the detection of advanced adenoma, 100% for
colorectal cancer, and 58% for advanced neoplasia, compared with
colonoscopy. In contrast, the sensitivity of GOBT was 9% for
detection of advanced adenoma, 23% for colorectal cancer, and 12% for
advanced neoplasia compared with colonoscopy. This superior
sensitivity was not obtained at the expense of specificity. Both
tests had a specificity of 92% or more for the detection of each of
these conditions compared with colonoscopy, with IOBT 2% to 5% less
specific than GOBT.

"And this was a study done with one-time screening," Dr. Quintero
told Medscape. "That means that if you repeat the test every year or
two, the sensitivity...is going to be much higher."

The relative risk for advanced neoplasia in patients with positive
results on a fecal occult blood test was 4.8 for the GOBT compared
with 25.7 for the IOBT.

"We have to change our test for screening colorectal cancer," said
Dr. Quintero. He added that the IOBT has already been approved by the
Food and Drug Administration and is available in the U.S.

WCOG 2005: Abstract DR 0527. Presented Sept. 13, 2005.

Reviewed by Gary D. Vogin, MD