9.APR.2020 6 MIN READ | 6 MIN READ

Learn more about colon cancer, and how a colonoscopy can help to detect the condition early.

What is colon cancer?

Also known as colorectal cancer, colon cancer is a serious malignant disease that affects the colon – the final part of the digestive tract. Cancer can occur in any part of the colon, generally divided into the right colon and left colon (including the rectum). The majority of cancers occur in the left colon, although some genetic cancers tend to occur more in the right colon.

Unique to cancers, colorectal cancer always starts from polyps – a noncancerous type of growth that forms along the inside of the colon. This feature provides a great opportunity to prevent colorectal cancer altogether by detecting polyps that have the potential to become cancerous and removing these polyps. While some individuals with larger polyps may experience symptoms like blood in the stool or constipation, these polyps seldom cause any symptoms at all. Hence, screening for asymptomatic colon polyps is very helpful in colorectal cancer prevention.

Should I be concerned about colon cancer?

Colon cancer risk factor
In Singapore, colorectal cancer remains as one of the most common cancer among men. According to the Singapore Cancer Registry, it is also consistently among the leading cancers in the country, with 10,634 new cases diagnosed (nearly 6 cases per day) and 4,082 deaths in in 2013 – 2017. In the past 50 years, colon cancer made up more than half the cases of colorectal cancer in Singapore, and this trend was also observed in other countries.

Even though this ailment is seen more commonly in people aged 50 and above, some types, especially those that have genetic linkages can occur at any age. Other potential factors that increase one’s risk include:

  • Diet: Low-fibre, high-fat diets that include red meat and processed meat may lead to a higher risk of colon cancer
  • Ethnicity: Singaporean-Chinese have a higher risk of colon cancer compared to other races in Singapore
  • Family history: 5 – 10% of all colon cancers may be hereditary, and may develop in individuals before the age of 50
  • Lifestyle habits: A sedentary lifestyle, as well as excessive smoking and drinking, may all contribute to the risk of developing colon cancer

What are some symptoms of the disease?

In the early stages of colon cancer, there are usually no symptoms to warn patients. However, in the later stages of cancer, some signs include:

  • Blood in the stools
  • Change in bowel movements and habits (such as increased frequency of diarrhoea or constipation or alternating diarrhoea and constipation)
  • Unintended and unexplained weight loss
  • Abdominal discomfort
  • Weakness or fatigue

As these symptoms are usually more obvious in later stages of the cancer, it is recommended to go for regular medical check-ups for early detection. One of the ways you can go about ensuring that your colon is healthy is to sign up for a screening colonoscopy from the age of 50. If there is a family history, especially of a first degree relative, of colorectal cancer especially at a younger age (say below 60), the age to start colonoscopy screening should be advanced to about 10 years younger than the age of diagnosis of that relative’s cancer.

What is a colonoscopy and what happens during the process?

Colon cancer colonoscopy
A colonoscopy is a medical test that examines your rectum and colon to investigate symptoms that may originate from the colon and rectum.

During colonoscopy, a thin flexible tube called a colonoscope is inserted into the rectum. A tiny but high resolution video camera at the tip of this tube allows your doctor to view the insides of the entire colon. The tube can be advanced to the end of the colon and can even enter the terminal ileum, which is the last part of the small intestine that joins the colon. Abnormalities of the lining of the colon and terminal ileum can be seen during colonoscopy and biopsies can be taken by means of forceps that are advanced through a working channel in the colonoscope. If polyps are seen, these can be excised by instruments such as a diathermy snare that is passed through the working channel.

Removal of polyps is called polypectomy. Colonoscopy is a comfortable test because patients are usually given mild sedative medications during the procedure so that there is minimal, if any discomfort. If a polyp is too large to be removed via colonoscopy, biopsies will taken to determine its nature. Sometimes, a mass is evident which looks malignant on visual inspection and biopsies will be taken to confirm if it is indeed a cancer.

Based on international guidelines, if a first screening colonoscopy is negative and there is no family history or suspicion of genetically mediated colorectal cancer, screening colonoscopies can be done once in up to 10 years. However, the intervals that are appropriate for particular patients should be discussed with their doctors.

I’m going for a colonoscopy. How should I prepare beforehand?

Some preparation is necessary prior to colonoscopy to ensure a successful procedure.

  • Before you can have a colonoscopy, your bowels have to be empty and clean.
  • Several days before the procedure, you may be asked to go on a low-fibre diet, which means no grains, nuts, seeds or fruits and vegetables.
  • You will need to fast for at least 8 hours before the procedure, although sips of water will generally be allowed. For a morning procedure, fasting from midnight is usually sufficient.
  • Bowel preparation by laxatives will be necessary to ensure a clean colon. Your doctor will prescribe specific laxatives and a schedule for taking these, as is appropriate to you.

Are there other options to screen for colon cancer?

There are several options available:

1) Faecal Immunochemical Test (FIT)

 The Faecal Immunochemical Test (FIT) is one of the more convenient screening options, and you can get a kit to carry out the procedure on a recommended schedule from your own home. This preliminary test helps doctors ascertain the health of your colon by checking for traces of blood in your faeces that are invisible to the naked eye (“occult blood”). As a rule of thumb, it is recommended to take this test once a year. The advantage of this test is that it is convenient and non-invasive. The disadvantage is that not all polyps shed blood and may thus be missed and by the time occult blood is evident, the polyp may be larger, or there may already be a cancer. There can also be false positive tests (eg. bleeding from other sites in the digestive tract from mouth to small intestines) that will lead to a colonoscopy.

2) Virtual colonoscopies

Virtual colonoscopies – also known as computed tomography or CT colonography – employ x-rays to detect polyps. The advantage is that is non-invasive. Bowel preparation is still required and a lot of air is pumped into the colon making the procedure a bit uncomfortable. Further, it is difficult on the images to distinguish adherent lumps of faeces from polyps, thus necessitating a colonoscopy. In any case, biopsies and polypectomy are impossible with CT colonography and any finding would inevitably lead to a colonoscopy.

To learn more about colon cancer and whether you should be screened for this, make an appointment with a specialist for a full discussion.


Article reviewed by Dr Tan Chi Chiu, gastroenterologist at Gleneagles Hospital, Singapore


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Tan Chi Chiu
Gleneagles Hospital

Dr Tan Chi Chiu graduated from the National University of Singapore in 1983. He pursued specialist training in Internal Medicine and obtained his Memberships of the Royal Colleges of Physicians of the United Kingdom and Ireland, as well as his Master of Medicine in Internal Medicine in 1988. Dr Tan specialised in Gastroenterology and was accorded the Fellowship of the Academy of Medicine in Gastroenterology in 1993 and recognised by the Ministry of Health as a specialist in Gastroenterology. He was further conferred the Fellowships of the Royal Colleges of Physicians of Edinburgh and London in 1996 and 1998 respectively.