Primary prevention

 

Primary prevention is of utmost importance for prevention of Colorectal Cancer (CRC) as many of the risk factors are modifiable. For preventing CRC, the Cancer Expert Working Group (CEWG) of Hong Kong Centre for Health Protection recommends the population to:

• Increase intake of dietary fibre (e.g. fibre from at least five servings of fruits and vegetables

daily);

• Decrease consumption of red and processed meat;

• Take part in moderate-intensity aerobic physical activities for at least 150 minutes per week;

• Maintain  a  healthy  body  weight  with  body  mass  index  between  18.5  to  22.9  and waist

circumference less than 80 cm for women and 90 cm for men;

• Avoid or quit tobacco smoking; and

• Avoid alcoholic drinks.

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Secondary Prevention

 

Secondary prevention means screening, i.e. examining people without symptoms in order to detect disease  or  identify people  at  increased  risk of disease. Since CRC arises predominantly from precancerous adenomatous polyps developed over a long latent period, it is one of the few cancers that can be effectively prevented through organized and evidence-based screening. In general, subjects to consideration for colorectal cancer screening, people can be classified into “average risk” and “increased risk” groups.

 

According to screening recommendations made by the CEWG, people with “increased risk” refer to individuals who have a significant family history, such as those with an immediate relative diagnosed with colorectal cancer at the age of 60 or below; or those who have more than one immediate relatives diagnosed with colorectal cancer irrespective of age at diagnosis; or those who have immediate relatives diagnosed with hereditary bowel diseases. People with “average risk” refer to individuals aged 50 to 75 who do not have the aforesaid family history.

 

Screening for general population at average risk

 

Since 2010, the CEWG recommends that average risk people aged 50 to 75 should consult their doctors to consider one of the following screening methods:

• annual or biennial faecal occult blood test (FOBT);

• sigmoidoscopy every 5 years;

• colonoscopy every 10 years.

 

The CEWG made the above recommendations after taking into consideration local epidemiology, research evidence as well as overseas guidelines and practices.

 

The age range recommended for CRC screening in the general population should be defined to capture the largest number of CRC cases while taking into account effectiveness and cost-effectiveness of screening tests, local epidemiology as well as anticipated benefits and harms to the screened population. In Hong Kong, the risk of CRC increases significantly from age 50 onwards1. Guidelines in U.S. and Singapore recommend the starting age of screening at 50 while U.K. recommends screening to start at above 50 years of age.

 

Regarding screening modalities, faecal occult blood test (FOBT), sigmoidoscopy and colonoscopy have been shown to reduce mortality from CRC based on research evidence. FOBT could reduce CRC mortality ranging from 15 to 33 % according to findings from large-scale randomized control trials (RCTs). A Cochrane review showed that screening by FOBT might reduce CRC mortality in average risk population by 16%. Sigmoidoscopy was shown to lead to 28% risk reduction in overall CRC mortality and 43% risk reduction in distal CRC mortality in a meta-analysis . Colonoscopy was associated with 61% reduction in CRC mortality in a meta-analysis.

 

Also, overseas guidelines and practices for CRC screening in the general population mainly recommend annual or biennial FOBT, sigmoidoscopy once every 5 years or colonoscopy once every 10 years.

 

To reduce burden arising from CRC, the Government launched the three-year Colorectal Cancer Screening Pilot Programme (“Pilot Programme”) on 28 September 2016 to provide subsidized screening by phases to average risk Hong Kong residents born in 1946 to 1955. The screening workflow comprises two stages. Participants would first receive subsidised Faecal Immunochemical Test (FIT, a new version of FOBT) from enrolled Primary Care Doctor (PCD). If the FIT result is positive, the participant would receive subsidised colonoscopy examination service from enrolled Colonoscopy Specialist. Persons at average risk who are not currently covered by the Pilot Programme may consult their family doctors about the need for colorectal cancer screening. Details of the Pilot Programme are available at www.colonscreen.gov.hk.

 

Screening for individuals at increased risk

 

The CEWG updated in 2017 the CRC screening recommendations for individuals at increased risk, with the key change relating to the interval for colonoscopy screening among individuals with significant family history of CRC but without mutated gene:-

• For carriers of mutated gene of Lynch Syndrome, the CEWG recommends screening for colorectal cancer (CRC) by colonoscopy every one to two years from age 25 onwards.

• For carriers of mutated gene of FAP, the CEWG recommends screening by sigmoidoscopy every two years from age 12.

• For individuals with one first-degree relativei diagnosed with CRC at or below 60 years of age or more than one first-degree relatives with CRC irrespective of age at diagnosis, colonoscopy should be performed every five years (instead of every three to five years) beginning at the age of 40 or ten years prior to the age at diagnosis of the youngest affected relative, but not earlier than 12 years of age.

 

For CRC patients with identifiable genetic mutations (namely the Lynch Syndrome and FAP), the CEWG recommends two-tier screening for their family members. Genetic testing should first be conducted followed by endoscopic examination at specified and shorter intervals if genetic test is positive. This is to reduce the number of unnecessary investigations among those with strong family history but without proven gene mutation to reduce the risk of potential complications arising from repeated endoscopic procedures.

 

The CEWG made the above recommendations after taking into consideration scientific evidence as well as overseas guidelines and practices.

 

Persons who are carriers of mutated gene of FAP or Lynch Syndrome and individuals with family history of CRC are at higher risk of colorectal cancer. CRC in these individuals tends to be diagnosed at a younger age and progresses more aggressively than CRC in the general population.

 

Overseas recommendations emphasize that CRC screening in high risk individuals needs to start earlier in their lifetime and be repeated at shorter intervals. Recommendations made by countries and by professional organizations on screening for persons at increased risk generally suggest the use of colonoscopy and sigmoidoscopy as the screening methods.

 

The recommended endoscopic screening method for mutated gene carrier of Lynch Syndrome is annual or biennial colonoscopy. The recommended age of onset of screening may vary from 20 to 25 in US and Singapore in UK , and 25 or five years earlier than the age of diagnosis  of the youngest affected member of the family (whichever is the earliest) in Australia . The guideline issued by the World Gastroenterology Organization (WGO) recommended that screening should start at the age of 20 to 25 or 10 years earlier than the youngest age of CRC diagnosis in the family, whichever comes first.

 

The recommended endoscopic screening method for mutated gene carriers of FAP is mainly annual or biennial flexible sigmoidoscopy, or annual colonoscopy. The recommended age to commence screening varies between 10 to 12 years in US and Singapore in UK and 12 to 15 (later age is recommended) in Australia. The guideline issued by National Comprehensive Cancer Network suggests screening should start at the age of 10 to 15 while WGO’s recommendation is to start at 10 to 12 years of age.

 

Overseas guidelines recommend endoscopic screening for individuals who have one first degree relative diagnosed with CRC between age of 50 and 60. Moreover, overseas guidelines also consider individuals with more than one first-degree relatives with CRC irrespective of the age at diagnosis being at increased risk and recommend more frequent endoscopic screening. The recommended endoscopic screening method is to receive colonoscopy every 5 years. The age to start screening is age 40 or 50, or 10 years prior to the age at diagnosis of the youngest affected relative.

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