Screening for colorectal cancer
Dr Zee Ying Kiat from Parkway Cancer Centre addresses commonly-asked questions.
What are the different methods of screening for colorectal cancer, and what are the differences between the methods?
Screening is the process of looking for cancer in people who have no symptoms of the disease. If colorectal cancer screening reveals a problem, diagnosis and treatment can occur promptly. Colorectal cancer is generally more treatable when it is found early, before it has had a chance to spread.
Doctors may suggest one or more of the following tests for colorectal cancer screening:
- Faecal occult blood test (FOBT): This test checks for hidden blood in faeces (stool). Studies have shown that FOBT, when performed every one to two years in people aged 50-80, can help reduce the number of deaths due to colorectal cancer by 15-33 per cent.
- Sigmoidoscopy: In this test, the rectum and lower colon are examined using a lighted instrument called a sigmoidoscope. Precancerous and cancerous growths in the rectum and lower colon can be found and either removed or biopsied. Studies suggest that regular screening with sigmoidoscopy after age 50 can help reduce the number of deaths from colorectal cancer. A thorough cleansing of the lower colon is necessary before this test.
- Colonoscopy: In this test, the rectum and entire colon are examined using a lighted instrument called a colonoscope. Precancerous and cancerous growths throughout the colon can be found and either removed or biopsied, including growths in the upper part of the colon, where they would be missed by sigmoidoscopy. However, it is not yet known for certain, whether colonoscopy can help reduce the number of deaths from colorectal cancer. A thorough cleansing of the colon is necessary before this test, and most patients receive some form of sedation.
- Virtual colonoscopy: In this test, special X-ray equipment is used to produce pictures of the colon and rectum. A computer assembles these pictures into detailed images that can show polyps and other abnormalities. It is less invasive than standard colonoscopy and sedation is not needed. A thorough cleansing of the colon is necessary before this test. Whether virtual colonoscopy can reduce the number of deaths from colorectal cancer remains unknown.
- Double contrast barium enema (DCBE): In this test, a series of X-rays of the entire colon and rectum are taken after the patient is given an enema with a barium solution and air is introduced into the colon. The barium and air help to outline the colon and rectum on the X-rays. DCBE may miss small polyps. It detects about 30-50 per cent of the cancers that can be found with standard colonoscopy.
What is the earliest stage that colorectal cancer can be detected by screening?
Screening can potentially detect colorectal cancer at its earliest stage. This is important as colorectal cancer is generally more treatable when it is found early, before it has had a chance to spread.
In many cases, screening can also prevent colorectal cancer altogether. This is because some precancerous polyps can be found and removed before they have the chance to turn into cancer.
Should people with a family history of colorectal cancer begin screening for it earlier?
People with a strong family history of colorectal cancer are at increased risk.
If you think you have a strong family history, you should see your doctor. A referral may be made to a genetics clinic, where your family history will be analysed to help work out the likely risk of a particular disease.
Early screening for colorectal cancer is recommended for those with a family history of familial adenomatous polyposis (FAP) or hereditary non-polyposis colorectal cancer (HNPCC).
Common symptoms
Colorectal cancer does not usually produce symptoms early in the progress of the disease. In fact, more than half of the people diagnosed have no symptoms.
When symptoms appear, they are likely to vary, depending on the size and location of the cancer. The common symptoms are:
- A change in bowel habits, including diarrhoea or constipation
- Presence of blood in the stool
- Persistent abdominal discomfort, such as cramps, bloating or pain
- A feeling of incomplete bowel emptying
- Unexplained weight loss
