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Bowel Cancer
Bowel Cancer is a usually a cancer of the large bowel, rarely of the small bowel. Here we discuss cancer of the large bowel, its causes, symptoms and treatment.
Fortunately, cancer of the bowel can often be cured by surgery, IF found early. Complete cure in large bowel cancer depends on early diagnosis. If people wait too long before reporting symptoms, the opportunity to remove the cancer completely may be lost.
What causes bowel cancer?
Doctors have discovered that large bowel cancer develops because of defects in the genes of cells lining the bowel. These cells multiply and form a small protrusion or ‘poylp’ on the bowel surface. The majority of polyps remain localized and cause no symptoms.
However, further changes can occur in the cells within a polyp, which cause them to become cancerous. This is why removal of polyps can prevent cancer.
Cancer develops when cells begin to multiply at an abnormal rate. Normally cells die and are replaced, the whole process is self-regulated. When cells begin to multiply at a faster rate than they should, a growth forms of all the unwanted cells. This can go on to a form a cancerous growth. The characteristics of cancer cells are that they invade the surrounding normal tissue and may spread to other organs. The reason for the altered behavior of cells is linked to an abnormality in their genes. It is known that a number of specific gene abnormalities (or mutations’) play an important part in cancer development and spread. People can be born with these gene mutations, in which case other family members may also have an increased risk of several types of cancer, or these genetic abnormalities can arise during a person’s lifetime. As a consequence of these accumulated genetic abnormalities either the destruction of abnormal cancer cells by the body’s natural defences is prevented or rapid, uncontrolled growth of cancerous cells starts.
The medical fraternity still does not know the causes of the genetic defects, although some of these gene defects probably originate because of our diet.
Patients with some long-standing inflammatory diseases of the bowel, such as Crohn’s disease or ulcerative colitis, may also have an increased risk of developing bowel cancer.
What protects against bowel cancer?
A diet rich in fresh vegetables and fruit and plenty of fibre seems to help protect against bowel cancer and there is some evidence that a diet containing much meat may increase the risk. There is also evidence that patients who regularly take anti-inflammatory drugs, such as aspirin, may be at a lower risk of developing cancer, but at the moment it is felt that the potential risks of taking aspirin regularly outweigh the benefits.
What are the symptoms of bowel cancer?
Often a bowel cancer causes no symptoms at the beginning. Patients go to doctors because they noticed blood in the motion (stool) or changes in bowel habit, such as unusual episodes of diarrhea or constipation or an increased amount of mucus in the stool. It can also cause a partial or complete blockage of the bowel leading to abdominal pain, windy distension (bloating) and, in severe cases, vomiting.
If small amounts of bleeding go on for some time, anaemia may cause tiredness and decreased ability to work and exercise.
Weight loss is usually a late symptom. Sometimes a cancer can perforate a hole through the bowel wall, so that bowel contents leak into the abdomen. This causes severe pain and the need for urgent surgery.
How is the diagnosis made?
One diagnostic test is an X-ray examination using barium to outline the bowel (barium enema). Small tube is placed in the rectum/anus and the liquid barium and some air are introduced, with the patient on the X-ray table. The barium outlines the bowel and X-rays are taken to show any irregularity in the bowel wall caused by the cancer.
An alternative X-ray diagnostic test used by a few hospitals uses just air without barium. The X-rays are taken by a CT scanner rather than an ordinary X-ray machine. Called a CT – Pneumo Colon ( i.e – CT with air in the bowel)
Thirdly, an examination can be made with a flexible telescope passed up from the anus. A sigmoidoscope can examine the lower bowel; a colonoscope is longer and can examine the whole of the large bowel. If any abnormality is seen, a small sample (biopsy) can be taken for analysis.
To help decide precise treatment it may be necessary to see the extent of the cancer and so a scan may be arranged.
How are cancers within a polyp treated?
When polyps are found they can often be removed using a colonoscope. A wire ‘snare’ is maneuvered around base of the polyp, tightened, and the polyp is separated from the bowel wall by passing a small electric current through the wire.
After the removal of a polyp, it will be examined using a microscope. Usually the polyp is made up of abnormal cells, but these are not cancerous. Sometimes an area of cancer is found within a polyp. If the cancer is confined to the polyp its removal is curative. If the examination suggests there is a risk that the cancer cells are not completely removed, a second colonoscopy or an operation to remove that part of the bowel will be advised.
How are cancers not confined to a polyp treated?
By the time of diagnosis, most cancers are situated within the bowel wall and there may be no evidence of the original polyp. Such cancers require an operation for their removal, but the type of operation will vary depending on where the cancer is. Sometimes it is not possible to join the bowel back together and so an opening (stoma) onto the skin of the abdomen may have to be made. Nowadays it is rarely necessary for such a stoma to be permanent. If it is temporary, it will be closed at a second operation after recovery from the initial surgery.
Sometimes the doctors may feel that there is a better chance of completely removing the cancer if it treated with radiotherapy or a combination of radiotherapy and chemothereapy (with drugs) before the operation.
What happens after polyp or cancer removal?
A person who has developed one or more polyp(s) may develop others years later. Another colonoscopy may therefore be advised after an interval. It is also known that patients who have had a bowel cancer have an increased risk of developing another. Some surgeons will routinely check the bowel with colonoscopy a year or more after an operation for removal of a cancer.
Advanced bowel cancer
Advanced bowel (colorectal) cancer is when the disease has spread from the large bowel to other sites around the body. This can occur when the disease is first diagnosed or when the disease has recurred at a later stage. Chemotherapy in this situation can be effective in controlling symptoms and prolonging life.
However, chemotherapy does not cure the disease and treatment is selected to provide a balance between the possible side effects and the benefit that may be gained from treatment.
Are there any implications for relatives?
If a person is young (less than 45-50 years old) when he or she develops bowel cancer, or if cancer is very common in the family, it may be that there is an inherited genetic abnormality. In such circumstances the patient’s brothers, sisters and children should ask to be referred to a specialist for advice. Sometimes a blood test will be all that is necessary to check whether they have this genetic abnormality, but some relatives may be advised to undergo a colonoscopy.
There are uncommon inherited conditions including ‘familial adenomatous polyposis’ (FAP) in which numerous polyps develop and the cancer risk is greatly increased. The family of these patients has to be carefully screened.
What does the future hold?
Constantly new techniques, new drugs and anti-tumour vaccines are being found. Also, ways of treating the genetic abnormalities which are found in patients with bowel cancer are being investigated. In addition, new, simple ways of screening large groups of people without any abnormal symptoms are being developed, so that, in future, it will be easier to identify cancer at an early stage.
