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What's New in Colorectal Cancer Screening? |
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By: Dr Eu Kong Weng, Senior Consultant Surgeon
Department of Colorectal Surgery,
SGH Department of Surgical Oncology, NCC
Dr Lim Jit Fong, Registrar
Department of Colorectal Surgery, SGH
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Colorectal cancer (CRC) is currently
the most common cancer affecting men and women in Singapore. Data
from the Singapore Cancer Registry reported a steep rise in incidences
for age 50 years and above, peaking in the late fifties and early
sixties. Our incidence rate is similar to the highest incidence areas
in the world. By the time signs and symptoms are present, the majority
of patients are already in a late stage of the disease.
Signs and symptoms of CRC include: |
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- Bleeding from the rectum during bowel movement
- Bowel movements containing mucus or blood
- Diarrhoea, constipation, or feeling that bowel does not empty
completely
- Stools that are narrower than usual
- Abdominal pain or discomfort (bloating, fullness and/or cramps)
- Unexplained weight loss and pallor
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| These symptoms are also present
in other gastrointestinal-related non-cancer conditions. Therefore,
careful history taking and a physical examination by the doctor are
very important. |
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are 2 groups of target population where screening can benefit: |
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- Those at high risk of developing CRC (e.g. family members with
Familial Adenomatous Polyposis (FAP), immediate or close relatives
of patients with CRC)
- Those at moderate risk
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| Screening
tools currently available are: |
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- Symptom-based screening
- Faecal occult blood testing (FOBT) - most widely used
- Double-contrast barium enema (DCBE)
- Flexible sigmoidoscopy/colonoscopy
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FOBT
is a test to check for blood in the stool. However, it is not completely
accurate as dietary peroxidase from plant or meat products can give
a positive result. Some drugs can also give a false negative result.
Thus dietary restrictions are necessary to conduct this test. This
kit is available in Singapore as the Haemoccult II®.
DCBE is cheaper and less invasive
than a sigmoidoscopy or colonoscopy. It is a series of x-rays taken
of the large intestines after a patient is given an enema of a white
chalky solution to outline the colon on the x-rays. However, it is
known to miss small lesions.
Flexible sigmoidoscopy is an examination
of the rectum and lower colon with a light source on a narrow flexible
tube. It has been widely studied that 60-70% of CRC are left-sided
and therefore within reach of the sigmoidoscope.
Colonoscopy is the gold standard
in screening for the high-risk population. It uses a light source
on a narrow flexible tube, a microscope and camera to view the rectum
and entire colon. It also enables samples of tissue to be taken for
testing. Its cost and complication rates have prevented it from a
wider role in screening for the moderate risk population.
As we look to the future, newer tools are being developed for imaging
of the gastrointestinal tract. These include virtual colonoscopy (also
called CT colonography) and capsule endoscopy (where a patient swallows
a minute electric capsule and periodic transmission of data allows
clinical information to be collected; the capsule exits the body through
normal bowel movement).
In summary, there is compelling evidence that screening improves cancer
survival. It would therefore appear prudent to start screening the
population at the age of fifty. We have yet to start a nationwide
screening program for CRC like what we have now for breast cancer
but we hope to have one soon. The issues, which will affect the decision,
are compliance, sensitivity of the screening tool, cost and legislation.
References |
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- Chia KS, Seow A, Lee HP, Shanmugatharatnam K. Cancer incidence
in Singapore 1993-1997. Singapore Cancer Registry Report No 5.
- Hardcastle JD, Chamberlain JO, Robinson MHE et al. Randomized
controlled trial of faecal-occult-blood screening for colorectal
cancer. Lancet 1996, 348: 1472-1477.
- Kronborg O, Fenger C, Olsen J, Jorgensen OD, Sondergaard
O. Randomized study of screening for colorectal cancer with faecal-occult-blood
test. Lancet 1996, 348: 1467-1471
- Winawer SJ, Stewart ET, Zauber AG, Bond JH, Ansel H, Waye
JD, et al. A comparison of colonoscopy and double-contrast barium
enema for surveillance after polypectomy. National Polyp Study
Work Group. N Engl J Med
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