For Part 1 of the forum, we have Dr Eugene Yeo give us a presentation on the epidemiology of colorectal cancer, risk factors, and how we can prevent colorectal cancer. We then have Dr Toh Ee-Lin share on the different screening modalities available.
In Part 2, Dr Eugene Yeo and Dr Toh Ee-Lin go through many questions posted by our enthusiastic audience, both collated from the registration process, and also posted LIVE. Read below to find out more about colorectal cancer.
VIDEO
Presentation by Dr Eugene Yeo
Introduction
Over the last 20 years, the number of cases of cancer has doubled. With our healthcare system getting better, we live longer and also get better at detecting cancer. Cancer is also the top cause of death in Singapore. The later we discover the cancer, the poorer the survival rate.
Epidemiology
Colorectal cancer is the most common cancer in males, and the second most common cancer in females in Singapore. Colorectal cancer is mostly found in Stage 3 in both male and females in Singapore. Generally, colorectal cancer is found in the lower part of the colon – the sigmoid colon and the rectal – makes up for almost 50% of total cases.
How does colorectal cancer develop?
Colorectal cancer develops from polyps (small growths in the intestine). Known as the polyp to cancer sequence, the cells in the polyp change to a type of cell that is no longer able to be controlled. Uncontrolled cell growth invades the lining of the stomach, the muscle, and eventually becomes a cancer that spread to the rest of the body. Normal colon cells replenish themselves through cell division. With every division, there is a chance that a DNA mutation can occur. Over millions of divisions, the number of mutations that occur add up and eventually comes to a point where the cell is no longer able to control its death anymore. It takes about 5-10 years for the mutations to end up becoming cancer. This may be shortened for patients already born with certain mutations in their DNA.
Risk factors
There are two types of risk factors for colorectal cancer:
1. Unmodifiable risk factors
50 is the age where risk of colorectal cancer develops significantly. However, there is an increasing incidence of colorectal cancer in young patients (under the age of 50). Since 1994, there has been an increase of almost 2% per year globally. Fortunately, if you are diagnosed early, there is still a good chance of a cure.
Chinese males are at higher risk of getting colorectal cancer
Each first degree relative with colorectal cancer doubles your risk of developing colorectal cancer.
Underlying Medical History
If you have had cancer before, you are at a higher risk of developing colorectal cancer. Previous polyps, inflammatory bowel disease also increases your risk of cancer. Polyposis/non-polyposis syndromes start you off at a later stage in the polyp to cancer sequence, resulting in an increased risk of colorectal cancer.
2. Modifiable
Red and processed meat have a very strong relationship to cancer. Processed meats belong in Group 1 (Causes cancer) of the IARC Carcinogenic Classification Group, while red meats (including pork, beef, and lamb) belong in Group 2A (Probably causes cancer) of the Classification Group. When our body breaks down and digests these meats, it forms N-nitrosyl compounds which cause DNA damage and mutation. High intake of red meat (>160g/day) is associated with 30% increase in risk of colorectal cancer compared to low intake (<20g/day).
Fibre has an inverse correlation with cancer – the more fibre you take, the lower your risk of colorectal cancer by up to 40%.
It is recommended to perform 150 minutes of exercise per week, split up into 3 sessions. Any form of exercise is acceptable, and can decrease risk of other cancers as well. Obesity also increases the risk of cancer.
Smoking and alcohol is unhealthy in general and not just for colorectal cancer. 1 pack of cigarettes a day and heavy drinking (> 4/day for women, > 5/day for men) increases the risk of colorectal cancer by 50%.
Presentation by Dr Toh Ee-Lin
Screening
Symptoms of Colorectal Cancer
The most common symptoms of Colorectal Cancer include:
Persistent change in bowel habit – consistency, frequency
Constipation, diarrhoea, alternating
Decrease in stool caliber
Rectal bleeding
The feeling of incomplete evacuation of stools
Symptoms of blood loss: eg Lethargy, palpitations, giddiness
Abdominal pain or bloating
Loss of appetite, loss of weight
Early colorectal cancer may be asymptomatic. Ideally, we should diagnose and detect polyps before they turn into cancer.
Risk group classification
Singapore classifies the risk of developing colorectal cancer into Average Risk, Increased Risk, and High Risk.
Increased Risk and High Risk patients are those with inherited conditions for example polyposis syndromes, inflammatory bowel disease patients, and those with a first-degree relative diagnosed with colorectal cancer.
Those that are at average risk are:
Age 50 and above
Asymptomatic
Non-first degree relative with colorectal cancer
Screening modalities available to those from this risk group are Faecal Immunochemical Test (FIT) (stool test for occult blood), Colonoscopy, and CT Colonography.
Faecal Immunochemical Test (FIT)
The ideal test is easily accessible, safe, non-invasive, cheap, accurate, and easy to perform. The FIT detects blood in the stools that is not visible to the naked eye. If you have already noticed blood in your stools, this test will not be suitable for you. The recommendation is for this test to be done on 2 separate occasions, with a yearly interval. The sensitivity of this test in detecting polyps is 73%, and the next step for a positive FIT test will be a colonoscopy. However, this sensitivity drops to 5% when it comes to detecting polyps.
CT Colonography
This is essentially an X-ray examination to look at the insides of the colon. The accuracy of this modality exceeds FIT and can be used to detect polyps ≥ 6mm in size. Patients will still have to undergo bowel preparation for this test. Air will be pumped into the colon before the CT scan starts. The disadvantage of a CT colonography is that when we notice abnormalities, we do not have a scope inside the patient to remove the tissue for testing. Ultimately, these patients will have to undergo a colonoscopy to remove the abnormal tissue for testing.
Colonoscopy
This is the ‘gold standard’ for colorectal cancer screening. Colonoscopy is done under conscious sedation, where you are still able to support your own breathing, and your heart and respiratory rate are stable. You will be kept comfortable and unaware of the procedure, with most patients not remembering what happened during the procedure. Before undergoing a colonoscopy, you are required to do a bowel preparation to remove the stools and provide a clear view of the colon. With direct visualization of the internal lining, the accuracy is high with an accuracy of ≥ 95%. Another benefit of this test is that abnormal tissues and polyps can be removed at the same time, which is the most effective way of preventing colorectal cancer.
Faecal DNA/Multitarget stool DNA
This test is based on the shedding of the cancer cell into the gastrointestinal tract. This detects any DNA mutation and occult blood, with the sensitivity being 92%. However, this test is expensive (~600 USD) and does not give us more information than a colonoscopy can. This test is not approved for use in Singapore due to limited evidence.
There are also other blood-based tests such as SEPT9 assay and CEA tumour marker, but their ability to pick up cancer or polyps is low and there is no evidence for it. CEA tumour marker test is a very common blood test done and is usually included in part of a health screening package. However, it is not specific to colorectal cancer and is not recommended for screening. It can be used for monitoring recurrence or treatment response for patients who have already been diagnosed with colorectal cancer.
Final words
Early colorectal cancer may be asymptomatic, but screening of these asymptomatic individuals is important as it may allow colorectal cancer to be detected at an earlier stage. A colonoscopy is the ‘gold standard’ for colonic evaluation. Doing it timely and removing the polyps can prevent the polyp to cancer sequence, making it the best form of prevention for colorectal cancer.
What’s next in store?
See Part 2 for the Question and Answer (Q&A) segment with Dr Eugene Yeo and Dr Toh Ee-Lin!
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