Colorectal cancer is a cancer that develops from the cells of the large intestine. The large intestine consists of the colon and rectum. The rectum comprises the last 15 cm of the large intestine and lies within the pelvis, which consists of the hip bones. This is a very small area and the distance between the cancer and the surrounding normal organs is very short. Hence, the chance of the cancer spreading to neighbouring organs in the pelvis is significantly high.
The colon forms the rest of the large intestine that lies above the level of the hips. It is surrounded by fatty tissue, called omentum, and anchored by more fatty tissue (called mesentery) to the walls of the abdominal cavity. The lymph glands are in the mesentery.
Cancer can develop from the cell-lining of the large intestine. The cancer can cause blockage of the intestine, or bleeding in the faeces.
Colorectal cancer is now the most common cancer in Singapore affecting both males and females. There were about 11,238 cases diagnosed from 2014-2018 locally.
Most persons diagnosed with colorectal cancer are older than 45 years of age. Younger persons, below 20 years of age, if diagnosed to have colorectal cancer, are likely to have the hereditary form of colorectal cancer such as familial adenomatous polyposis.
Common symptoms that persons have are a change in bowel habits, such as persistent diarrhoea or constipation or a change in the frequency of stools. Passing blood mixed with stools is also a suspicious sign which always requires prompt medical attention.
Other symptoms include persistent ill-defined abdominal discomfort or pain. Occasionally, a mass is felt in the abdomen.
The risk of colorectal cancer is increased when there is:
The simplest way to detect a rectal cancer is by insertion of the doctor's finger into the rectum, i.e. a rectal examination. This can be done in the outpatient clinic, takes less than 5 minutes and causes minimal discomfort. However, this detects cancers only in the last 5 to 8cm of the rectum.
For cancers that are more distantly located in the large intestine, sigmoidoscope or colonoscope examination can be performed. These fiber-optic flexible tubes are inserted up the rectum into the colon. Through these scopes, removal of a small piece of growth for testing is possible. Insertion of these scopes are performed with minimal anaesthesia in an outpatient clinic. Although uncomfortable, the procedure lasts less than 30 minutes.
Barium enema is an x-ray examination performed to examine the whole length of the large intestine. A dye is passed through a narrow tube into the rectum and allowed to coat the length of the intestine. Multiple x-ray films are taken on various portions of the large intestine and abnormal areas identified. The doctor may further proceed to do a colonoscopy or a sigmoidoscopy so that a biopsy of these suspicious areas can be done.
The mainstay of treatment is surgery. The cancer, its surrounding fat, and lymph glands are removed during surgery. The two ends of the cut section are joined together. If for some reason the colon cannot be joined, an artificial opening for the colon, called a colostomy, may be required. This opening allows waste to be removed from the body when the normal opening cannot be used or has to be removed. A colostomy may be temporary or permanent.
Depending on the stage of the cancer, chemotherapy may be required after surgery to improve a person's chance of cure from the cancer. Chemotherapy involves injections of anti-cancer drugs into a vein on the hand. Chemotherapy, which lasts from 6 to 12 months, usually causes mild mouth ulcers, mild diarrhoea, mild hair loss, possible darkening of complexion, and nausea. The most common medicine used is 5- fluorouracil, though other drugs may be also be used.
Again, the mainstay of treatment is surgery. Due to the position of the rectum in the bony pelvis, the chance of cancer radiation therapy is sometimes used to reduce the size of the colorectal cancer before surgery. More often, it is used after surgery to destroy any remaining cancer cells and prevent the cancer from recurring.
Radiotherapy involves giving high-energy rays into a small area where the original cancer was. The course of treatment, given daily for 5 minutes, usually lasts 5 to 6 weeks. Side effects which may occur include diarrhoea, tiredness, skin redness and rash. In some women, radiotherapy brings on early menopause.
As with colon cancer, chemotherapy may also be required, after surgery. Radiotherapy may be given together with chemotherapy.
A prognosis is the probable outcome of an illness based upon all the relevant facts of the case. All findings from clinical examination and x-ray investigations and pathology reports are important and must be considered together to decide what the progress of an individual case of colorectal cancer may be. From this, the appropriate course of treatment can be decided and put into action. The treatment strategy will vary from person to person. With prompt and appropriate treatment, the outlook for a person with early colorectal cancer is good.
Subscribe to our mailing list to get the updates to your inbox