Colorectal cancer (CRC) is an important health problem globally, as well as in Singapore. Locally, CRC remains the most common cancer, with 9,320 new cases of CRC diagnosed between 2010 and 2014. This works out to about 49 cases per 100,000 people. Based on local data, ethnic Chinese has the highest risk, when compared to their Malay and Indian counterparts.
Despite the advancement in CRC screening modalities, improved treatment of pre-cancerous growths and polyps as well as state of the art surgical techniques, chemotherapy and radiotherapy, CRC continues to remain the most common cancer in Singapore. A major reason may be due to poor screening uptake i.e. not many who will benefit from screening go for screening.
There is good evidence to demonstrate that CRC screening reduces CRC related deaths. It is well known that CRC generally develops from adenomas (also known as polyps). It is postulated that it takes about 10 years for a non-cancerous (benign) polyp to develop to cancer. This provides the rationale for screening to detect and remove these polyps, before they have a chance to develop cancer.
There are various screening strategies with different strengths and limitations. Individuals should discuss with their family doctors to assess their personal risk, and decide on a cancer screening strategy that best suits their needs.
Like all screening tests, CRC screening should be done to detect the disease early in people who are well, and who do not have symptoms.
There are several methods for CRC screening:
1. Stool test for occult blood
3. CT Colonography
Stool for occult blood is used to detect blood that is invisible to the naked eye. The presence of blood will necessitate further review with colonoscopy. The advantages of the stool test include cost (it is cheap) and convenience (can be done at the individual’s convenience). This should be done annually.
Colonoscopy involves inserting a small tube with a camera at its tip to inspect the large intestine (colon) via the anus. The patient will be sedated during the colonoscopy that usually lasts about 20 minutes. The advantage of colonoscopy is that it is accurate and considered the ‘gold standard’ for screening. Furthermore, any polyps can be visualized and removed during the procedure.
Computer Tomographic (CT) Colonography involves performing a CT scan focusing specifically on the intestines, and is sometimes also known as virtual colonoscopy. The advantage is that it is non-invasive. However, polyps 5mm or less may be frequently missed and removal of polyps cannot be performed. Onset of symptoms such as blood in stools, unexplained change in bowel habits and weight loss usually indicates that the disease may be advanced and one should consult a doctor for further evaluation without delay.
Screening should start from 50 years onwards for individuals who are completely well without medical problems. For those with first degree family members (parents or siblings) with CRC, screening should start 10 years earlier from the age of CRC diagnosis or at 50 years old, whichever is earlier. Other CRC risk factors include smoking, increasing age, inflammatory bowel disease and hereditary adenomatous conditions.
Those who opt for stool occult blood test should perform it annually. Those with completely normal good quality colonoscopy can have it repeated 10 years later, while those with completely normal CT Colonography can have it repeated 5 years later.
Individuals with abnormalities e.g. polyps seen on any of the screening modalities will be advised by their attending doctor depending on the abnormality detected.
The first step in our battle against Singapore’s most common cancer is to start screening. Discuss your risk with your doctor to consider your options for CRC screening today!
Publication: 15 December 2016