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. 

If colon cancer develops, many treatments are available to help control it, including surgery, radiation therapy and drug treatments, such as chemotherapy, targeted therapy and immunotherapy.

Signs and symptom

Colorectal cancer might not cause symptoms right away, but if it does, it may cause one or more of these symptoms:

  • A change in bowel habits, such as diarrhoea, constipation, or narrowing of the stool, that lasts for more than a few days
  • A feeling that you need to have a bowel movement that’s not relieved by having one
  • Rectal bleeding with bright red blood
  • Blood in the stool, which might make the stool look dark brown or black
  • Cramping or abdominal (belly) pain
  • Weakness and fatigue
  • Unintended weight loss

Colorectal cancers can often bleed into the digestive tract. Sometimes the blood can be seen in the stool or make it look darker, but often the stool looks normal. But over time, the blood loss can build up and can lead to low red blood cell counts (anemia). Sometimes the first sign of colorectal cancer is a blood test showing a low red blood cell count.

Risk Factors

  • 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.
  • 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.
  • 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. 
  • Smoking and alcohol consumption
  • Diabetes-People with diabetes or insulin resistance have an increased risk of colon cancer.
  • Sedentary lifestyle and obesity– People who are inactive are more likely to develop colon cancer. Getting regular physical activity may reduce your risk of colon cancer. However, physical activity improves the movement of faeces in the colon and can reduce risk.
Dietary Factors that may Increase Colorectal Cancer RiskDietary Factors that may Reduce Colorectal Cancer Risk
Processed and red meat Fruits and vegetables
Meat cooked at high temperaturesDietary fibre
  • Dietary Habits– Research has identified certain factors which can affect the risk of colorectal cancer:

 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.