How common is bowel/colon cancer?
Each year, 35,000 people in Britain are diagnosed with cancer of the bowel, that is to say cancer of the colon and rectum. This makes it one of the commonest cancers. But unlike some malignant tumours, bowel cancer can often be cured by surgery and new treatments are being introduced to make survival even more likely. The earlier the bowel cancer is diagnosed, the greater the likelihood of cure.
How does bowel cancer start?
Throughout our lives, the lining of the bowel constantly renews itself. This lining contains many millions of tiny cells which grow, serve their purpose and then new cells take their place. Each one of these millions of cells contains genes which give instructions to the cell on how to behave. When genes behave in a faulty manner, this can cause the cells to grow too quickly which eventually leads to the formation of a growth that is known as a polyp. This is the first step on the road towards cancer.
What is a polyp?
A polyp, or more strictly a particular type of polyp called an adenoma, starts as a tiny bump on the inside of the bowel. At first, the genes give instructions for the polyp to grow in an orderly manner. Some polyps remain very small throughout their lives while others grow slowly larger. At this stage, the lump is still benign. Most polyps remain benign throughout life but about one in 10 will turn into a cancer. Broadly speaking, the larger a polyp, the more likely it is to become cancerous – although cancer is unusual if the polyp is less than 1cm in diameter. We believe that all malignancies of the bowel probably start off as benign polyps. We know that removing benign polyps can prevent cancer developing later.
What protects against bowel cancer?
A diet rich in fresh vegetables and fruit and low in red meat seems to help protect against bowel cancer. A high calcium intake may be protective as may be the regular ingestion of some anti-inflammatory medicines such as aspirin although at the moment these are not used routinely.
What are the symptoms of bowel cancer?
The development of a bowel cancer from a polyp may take between five and ten years and early on there may be no symptoms at all. The most common symptoms are bleeding from the bowel, a change in bowel habit, such as unusual episodes of diarrhoea or constipation, or an increase in the amount of mucus in the stool. A bowel cancer can enlarge so that it partially or completely blocks the bowel leading to abdominal pain, constipation and bloating.
Sometimes tiny amounts of bleeding may go unnoticed but result in the development of anaemia which may cause tiredness and a decreased ability to work and exercise.
How is the diagnosis made?
Sometimes, the doctor will be able to detect a lump in the abdomen or on rectal examination but usually tests are needed. The most commonly used are:
- Flexible sigmoidoscopy – after an enemaa flexible telescope is passed through the anus, into the rectum and this can reach the lowest half of the colon
- Colonoscopy – this requires laxatives to clear out the bowel. A flexible telescope is passed through the anus into the rectum but the tube is long enough to examine the entire large bowel. The procedure is a little uncomfortable and most patients are offered an injection to ease any discomfort.
- CT scanning – this procedure has the advantage, (which many people appreciate) of not involving a tube being passed through the anus. It is not yet as reliable as colonoscopy and has the disadvantage of not being able to take a biopsy if required.
Both flexible sigmoidoscopy and colonoscopy have the advantage that a small sample or biopsy can be taken to look at under the microscope. The above tests are used in slightly different situations depending upon the symptoms that patients may have and the availability of the investigations.
What happens once cancer is diagnosed?
If you are found to have bowel cancer, a team of specialists is there to help. You will be advised to have blood tests and scans to determine what is known as the stage (extent) of the cancer. Not only will the size of the primary tumour be assessed as fully as possible but the specialist will also want to know if there is any sign of secondary spread. Armed with all the relevant information they have gathered about the cancer, the specialists will decide how best to advise you on the most appropriate treatment.
How are cancers of the colon treated?
Once a check has been made to see that there is no spread anywhere else most colon cancers are treated by surgery. This will usually involve removing the cancer together with the lymph glands alongside the blood vessels supplying that section of the bowel. In most cases, the two ends of the bowel are joined together again (anastomosis) but if the cancer has led to an emergency it may not be possible to join the bowel together straight away. Once the bowel cancer and surrounding tissue have been removed they will be examined under the microscope and only then will it be possible to determine fully the stage of the cancer. If the cancer is confined to the bowel wall then surgical removal alone may be all that is needed. If there is any sign of spread to the local lymph glands a course of chemotherapy postoperatively may well be advised.
Will a colostomy be necessary?
A cancer of the rectum very near the anal canal will be difficult to remove completely and in this situation it may be necessary to remove the rectum and the anus and make a permanent stoma or opening of the colon into the skin of the abdomen. This is called a colostomy. Fortunately, modern surgical techniques have made the need for a stoma to be much less likely nowadays than it used to be in the past.
Is there any screening for bowel cancer?
Mass screening of the population for bowel cancer involves testing the stools chemically for traces of blood, then carrying out further investigations of the bowel if the test is positive. Another technique of screening is to examine the lower part of the bowel with a flexible sigmoidoscope in persons between the ages of 55-65. Trials of using these techniques on individuals who have no bowel symptoms have shown that more early cancers are being diagnosed and that early detection improves your chance of survival.