Colorectal cancer is one of the most common cancers and among the most preventable cancers. Colorectal cancer, simply put, is the cancer involving the large intestine (colon and rectum). Here in Singapore, Colorectal Cancer is the most common cancer among men and the second most cancer among women. This make Colorectal cancer the most common cancer overall in Singapore.
Colorectal cancer usually develops from a “polyp” which is a non-specific term to describe a growth on the inner surface of the colon. Polyps are often benign (non-cancerous) growth but some can develop into cancer. Colonic polyps usually are asymptomatic, meaning they usually exhibit no symptom. They can continue to grow and develop without the body showing any symptom.
Detecting and removal of these colonic polyps are the keys to prevent colorectal cancer. This is where colonoscopic screening comes in.
There are 3 main groups of patients who need colonoscopic evaluation.
Asymptomatic individuals who are 50 years old and above
If you have no abdominal symptoms ad otherwise well, you will only need colonoscopic screening from the age of 50 years old and above. You only need to repeat the colonoscopic screening every 5 to 10 years after a normal colonoscopy.
Individuals with family history of colorectal cancer
Individuals with persistent symptoms suggestive of colorectal cancer
Colonoscopy is a specialized procedure whereby the lining of the entire colon and rectum is examined under direct visualization. This is performed via inserting a thin, flexible tube through the anus and advanced along the rectum till the scope reaches the beginning of the colon. During the examination, any polyp that is found can be removed via the endoscope and biopsy of the tissues can be taken for further test. It is usually done under sedation.
As mentioned earlier, detecting of polyps and their removal is the key to prevent Colorectal Cancer. This has been proven in large scale population studies. Studies also shown patients who have colorectal cancer diagnosed on screening colonoscopy usually have their colorectal cancer diagnosed at an earlier stage. This, in turn, leads to better outcome for the patients.
Patients undergoing colonoscopy need to have their bowel cleanse of stools and waste material. This bowel preparation is done by the patient ingesting special cleansing solution or laxatives. It is important to have cleanly prepared bowel during colonoscopic evaluation so that no fecal debris can obscure the identification of a polyp or small cancer. You are encourage to drink as much fluid as possible while taking your bowel prep. Usually you will be advice not to take any fibre (fruits and vegetables) 3 days before your procedure.
If your procedure is to be performed in the morning, you will be asked to take the bowel preparation laxatives the night before. If the procedure is to be performed in the afternoon, you will be asked to do take the laxatives in the morning.
If you are taking blood thinning medications like aspirin or Plavix, your colorectal surgeon will advice when to stop the medication.
The thought of undergoing colonoscopy can be quite intimidating and frightening. However, most patients who had undergone colonoscopy would testify that the colonoscopic evaluation was actually quite effortless. You will usually be given a sedation before the procedure.
Any polyp found during the colonoscopy is removed immediately and send for histological testing. Biopsy can be performed at area of interest to obtain tissue for histological examination. These procedures are usually performed with no discomfort to the patients.
Most patients have no discomfort after the colonoscopy. Very few patients may feel some abdominal bloatedness due to residual air in the intestines. This will usually settle by themselves with the passage of flatus. Most patients can resume normal diet after the procedure. You will be discharge after the procedure. If sedation was given, you will have to be accompanied home.
The results and the findings of the colonoscopic evaluation will be explained to you on the same day at the clinic of the colorectal surgeon. A report will be given to you at the same time.
As with any procedure, there are risks involved but the risks are very low. There are 2 main risks, post polypectomy bleeding and perforation. Post polypectomy bleed, if happens, occurs 7 to 10 days after the procedure. The incidence is very low (0.1% to 0.6%). In most cases, it is self limiting and can be treated conservatively. Perforation during colonoscopy is also very rare; it occurs in less than 1 in 1000 (less than 0.1%). If it occurs, surgery will usually be required to rectify it.
In the hands of experienced and skilled endoscopists, these risks are much lower.
There are 2 main alternatives to colonoscopy :- Barium enema and Computer Tomography (CT) Colonography. These are performed by radiologists. The main advantage is there is no need for tube to be inserted along the whole length. However tube is still needed to be inserted to introduce air and contrast medium into the anus and rectum. They are perceived to be less invasive. However these 2 methods also carried a risk of perforation in the region of 0.05% The disadvantages of these 2 methods are 1) exposure to X-Rays, 2) any polyps found cannot be removed and 3) small missed rate of polyps (1 to 5%).
The gold standard test is still the colonoscopy. Your doctor can discuss with you the pros and cons of each methods