Colon (Colorectal) Cancer

by Dr. Tan Huck Joo

Most people do not realise that cancer of the colon and rectum, commonly termed colorectal cancer, is one of the most common cancers in the world, causing 655,000 deaths annually worldwide. It is the most common cancer among Malaysian men, and the third most common cancer among Malaysian women.

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Colon cancer usually begins as a polyp, which is a small, mushroom-shaped growth on the colon's surface. Polyps are benign, but some can turn malignant. While not all polyps become cancerous, some are the precursors of colon cancer.

The good news is that colon cancer is preventable, and curable if detected early, hence the importance of screening.

What Are The Symptoms?

Colonic polyps and early colon cancer (stage 1, where the cancer is confined to the inner layer of the colon), in fact, cause no symptoms at all. At a more advanced stage, however, signs may include :

* Changes in bowel habits (probably the most significant symptoms), eg constipation, diarrhoea, or a feeling of incomplete emptying of the bowel

* Rectal bleeding

* Abdominal discomfort

* Unexplained weight loss

* Signs of anaemia, eg tiredness, shortness of breath

However, having some of the symptoms above does not necessarily mean that the patient has colon cancer. Other conditions may cause similar symptoms.

High-risk Factors

Colon cancer may occur in anyone. Although its exact cause is unknown, some risk factors include :

# Family history – If your parents or siblings had colon cancer before they turned 60, then you are more likely to get it.

# Age – Generally, the risk increases with age. This risk rises dramatically after 50.

# Ethnicity – Among the ethnic groups in Malaysia, colon cancer most commonly affects the Chinese community; the Chinese are 3 to 4 times more likely than Malays or Indians to suffer from it.

# Personal medical history – Women with a history of ovarian and uterine cancer have a higher chance of developing colon cancer. Patients with a previous history of colon cancer are also more likely to get it.

# Diet – A diet that is high in fat and calories and low in fibre is often associated with colon cancer. You should aim to increase your intake of cereals, fruits, and vegetables, and eat less meat, especially red meat.

# Lifestyle factors – Heavy alcohol consumption, smoking, and a sedentary lifestyle with little or no physical activity puts you at higher risk, as does being obese.

# Drugs – There is some evidence to suggest that certain drugs such as aspirin and anti-inflammatory drugs may be beneficial in reducing the risk of polyp growth, thereby reducing the risk of colorectal cancer. However, this is still speculative and is not standard practice.


Screening means looking for a tumour in someone with no symptoms and no personal history of colorectal cancer. Because colon cancer can strike without symptoms, it is crucial to be screened, or tested, by your doctor even if you have no symptoms.

The recommended age for screening via colonoscopy in many countries for average risk subjects is 50. This is mainly based on data from Western countries. Earlier screening is recommended for some high-risk groups, i.e. those who have a family history.

According to American College of Gastroenterology guidelines, if your parents or siblings had colon cancer at the age of 60 and above, then you should start screening at the age of 40. If they were diagnosed at less than 60 years old or if there are multiple siblings with the disease, then you should start screening at 40, or when you are 10 years younger than the youngest sufferers. For example, if your sibling had colon cancer at the age of 38, then you should be screened at 28.

Obviously, screening for colorectal cancer is an important step to prevent colon cancer. Apart from a colonoscopy, which is by far the best method, other methods of detecting colon cancer include faecal occult blood testing, the barium enema, sigmoidoscopy, and CT colonography.

Detecting Colon Cancer

When detected early, the survival rate for those who suffer from colon cancer is very good. Sadly, most people only see their doctors after the cancer has advanced. Most patients will not see their doctor until a few months after their symptoms first appear, and by this time, they are probably at stage 3 (advanced cancer) or 4 (when the cancer has spread outside the colon to other parts of the body such as the liver or the lungs).

Stage 4 is terminal cancer and chances of long term survival are very slim. Early diagnosis is the key and patients should seek immediate treatment as soon as they have symptoms of colorectal cancer.

If you see your doctor with symptoms of colon cancer, he will conduct a colonoscopy under light sedation. A colonoscopy is a daycare procedure where your doctor uses a colonoscope – a long, flexible tube about one centimetre in diameter attached to a video camera and monitor – to view and examine the entire colon and rectum.

During the procedure, your doctor can remove any polyps he finds or take biopsies or tissue samples for analysis. The removal of polyps reduces the risk of colon cancer.


Colonoscopy is useful to diagnose the problem and also to treat certain conditions such as bleeding, polyps, and blockages due to colon cancer.

A barium enema and CT colonography are occasionally useful to examine the rest of the colon beyond an obstructing tumour. The disadvantage of these tests in screening is that they are not able to detect 'small' cancers and your doctor will not be able to obtain tissue samples.

Blood tests to check for the tumour marker CEA (carcinoembryonic antigen) has a poor pick-up rate. The accuracy is approximately 20% to 40%. Besides, a raised CEA does not always mean colon cancer; it may also be elevated in patients with lung cancer or stomach cancer, and even in smokers. More importantly, a normal CEA does not exclude colon cancer.


* Surgery – A colon cancer patient's only hope for a cure is surgery. If the tumour is operable, i.e. if the tumour has not spread, then the tumour should be resected (the removal of all or a part of an organ). This removal method depends very much on the location of the tumour.

Some patients may require a temporary colostomy bag until the colon re-joined after a few months if the cancer is too near the anus. The earlier the cancer is detected, the higher the long-term survival rate for the patient.

Surgery is occasionally performed on patients with a bowel obstruction resulting from terminal cancer, to prevent bowel perforation. Colonic stenting (where a self-expanding wire mesh tube that is designed to hold open a blockage in the bowel is inserted) is an alternative to relieve the colonic blockage from colon cancer.

* Chemotherapy – The doctor uses drugs to stop the cells from dividing and/or kill the cancer cells. Most anticancer drugs are given by injection. Chemotherapy is indicated in more advanced diseases to kill cancer cells and prevent recurrence. This obviously has its side effects, but in general the drugs are tolerable.

* Radiation therapy – The use of high energy X-rays to kill cancer cells and to stop them growing. Radiotherapy is indicated for local disease control and is sometimes used in combination with chemotherapy to shrink a tumour before operation.

* Immunotherapy/Biological therapy – This therapy enhances the patient's anti-cancer resistance and uses the body’s own immune system to fight cancer, and to lessen the side effects of some anti-cancer treatment

Can Colon Cancer be Prevented?

Although the main risk factor for colon cancer is your genes, there is some evidence to suggest that you can prevent this cancer. You can do so by increasing your intake of fibre, i.e. from fruits and vegetables, and adopting a low-calorie diet. You can also stop smoking, cut back on or give up alcohol consumption, and get plenty of exercise.

Do note, however, that if you have a family history of colon cancer, you are at high risk of having it. This is why screening is of the utmost importance. Remember, colon cancer is preventable. So if you fall into the high-risk group, go for screening. Do not wait until you develop symptoms before you see your doctor.

More info on COLON CANCER here.

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