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colorectal cancer logoWhat Is Colorectal Cancer?

Colorectal cancer is cancer of the colon and rectum (or the large intestine), which is the last part of the gastrointestinal tract. When food enters the colon, water is absorbed and the food residue is converted into waste (faeces) by bacteria. The rectum is the terminal part of the colon that stores faeces before it is expelled through the anus. Polyps may form on the inner wall of the colon and rectum. These are benign lumps which are fairly common in people above the age of 50. However, certain types of polyps may develop into cancer and should be removed if they are detected. 


Certain characteristics of a polyp may indicate malignancy:

  • Polyps greater than 1 cm in diameter
  • Sessile polyps (i.e. polyps without a stalk)
  • Multiple polyps

In the early stages of colorectal cancer, the cancer cells are confined to the colon. If undetected, the cancer will develop and project into the lumen of the colon. It will also invade through the colon wall and spread by:

  • Invading neighbouring intestines and organs
  • Entering the lymphatic system and travelling into neighbouring lymph glands (mesenteric lymph nodes)
  • Entering the blood stream and travelling to the liver where secondary malignant deposits may form

Risk Factors

elderly couple1. Age
Men and women aged 50 years and above have an increased risk of colorectal cancer

2. Ethnicity
Among the races in Singapore, the Chinese have a higher risk of colorectal cancer.


3. Personal History

Individuals who have been detected with colorectal polyps or diagnosed with colorectal cancer in the past may be at a higher risk of experiencing a recurrence and are advised to seek regular screening.


4. Family History

Some individuals inherit a rare disease called familial polyposis in which many colorectal polyps develop at a young age. For these individuals, the risk of developing colorectal cancer is very high (80 to 100%). Such individuals should consider having the colon removed before the age of 40. Individuals who have relatives with polyps or colorectal cancer are also at a higher risk of colorectal cancer although this risk is lower compared to one with familial polyposis.


5. Ulcerative Colitis 

This is a disease affecting the bowels which, in the long term, leads to inflammation and cancerous changes. People with with this condition have a significant risk of colorectal cancer.


6. Drugs

Current users of HRT (hormone replacement therapy) are at a lower risk of colorectal cancer, although this protection disappears within 5 years of stopping HRT. Aspirin and NSAID (a strong painkiller drug) are known to reduce the risk of colorectal cancer. However, it is premature to recommend the routine use of these drugs for this purpose.


7. Sedentary lifestyle and obesity

These interrelated factors increase the risk of colorectal cancer. However, physical activity improves the movement of faeces in the colon and can reduce risk.


8. Dietary Habits

Research has identified certain factors which can affect the risk of colorectal cancer:

Factors that Increase Colorectal Cancer Risk
Meat cooked at high temperatures Contains chemicals that are carcinogenic
Animal fat Is converted to bile acids which can promote cancerous changes in the colon
Tobacco and alcohol Increase polyp formation

 

Factors that Reduce Colorectal Cancer Risk
Fibre (vegetables, fruits, bran) Improves the movement of faeces and dilutes the amount of carcinogens in the colon
Vitamin supplements Regular multivites and folates can reduce risk
Mineral intake Calcuim binds fatty acids and bile acids to reduce risk

 

Despite knowledge of these risk factors, the exact cause of colorectal cancer is unknown. It is estimated that 50 per cent of colorectal cancer patients have no known risk factors.