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Doctors' Notes

Polyps, the Root of Colorectal Cancer

Colorectal cancer is the most common cancer in Hong Kong. In 2016, the age-standardized incidence rates were 50.6 for male and 31.4 for female per 100,000 standard population. These figures are comparable to those in Western countries.

Colorectal cancer may occur in the colon or rectum. Most colorectal cancer cases are diagnosed at stage two or three. To reduce the chance of relapse, these patients are required to receive chemotherapy after having their tumours removed. The Faculty of Medicine of CUHK conducted researches on colorectal cancer screening which aims at early detection and treatment, leading to the initiation of the Government’s Pilot Programme. The second phase of the programme has been rolled out; Hong Kong residents aged 56 to 75 are subsidized to take a faecal occult blood test. If blood is found, colonoscopic check-ups will be arranged for further assessment.

Polyps are the culprit of colorectal cancer. The risk of developing into cancer for the adenomatous polyp is the highest. ‘If three or more polyps are found, or one is 1cm or larger, the person is considered at high risk. Among different types of adenomatous polyp, the villous adenoma has even higher risk of progression to cancer,’ said Prof. Simon Ng of the Department of Surgery. It takes five to 10 years for a polyp to turn into cancer. If no polyps are found in the colonoscopic check-up, patients are advised to have the check-up again after 10 years.

Age, smoking and alcohol consumption, low fibre intake, high consumption of red meat and obesity are risk factors for colorectal cancer. Family history of bowel cancer or hereditary bowel diseases also lead to higher risk. In recent years, another risk factor, ulcerative colitis, has been spotted. ‘Due to immune system dysfunction, patients who suffer from continuous bowel inflammation have a higher risk of progressing to colorectal cancer. The incidence rate of ulcerative colitis has increased six-fold in the past 30 years.’

Based on the above factors, CUHK developed the Colorectal-polyp Prediction Index, which allows the public to assess their chances of developing a high-risk polyp by completing a questionnaire. ‘Those classified as high-risk may consider having a colonoscopic check-up while others may simply have a faecal occult blood test.’

Thanks to the implementation of the Colorectal Cancer Screening Programme, a larger number of colorectal cancer cases can be detected early. Timely detection and removal of polyps could minimize the risk of developing cancer. ‘After 10 years, the incidence rate of the cancer will drop gradually,’ Professor Ng explained.

M. Mak

This article was originally published in No. 538, Newsletter in May 2019.

colorectal cancer colorectal cancer screening cancer polyps Simon Ng Department of Surgery Faculty of Medicine