Bowel cancer

The digestive system consists of the esophagus (the gullet) that leads into the stomach where the digestion of food is started. This then empties into the small bowel which is many yards long and where food is further digested and the nutrients absorbed into the bloodstream and which in turn leads to the large bowel (the colon) where waste matter is processed and then emptied to the outside world via the rectum (the last bit of large bowel) and anus (the exit).

Bowel cancer is the name given to cancer affecting either the colon or the rectum. The reason they are grouped together is that the causes, symptoms and treatment of cancer of the colon and rectum are similar and really the rectum is just an extension of the large bowel.

Bowel cancer is unfortunately very common, being the third most common malignancy after breast and lung cancer. It affects men slightly more often than women.

The likelihood of developing this type of cancer increases with age, being unusual under the age of 50 and far more common over the age of 70. However, in addition there are certain people at increased risk of this disease. Firstly, there are two inherited syndromes which can lead to bowel cancer at a relatively early age; one being something called hereditary non-polyposis bowel cancer (HNPCC) and the other being familial adenomatous polyposis (FAP).

People who have inherited the HNPCC gene account for between two and five per cent of cases of bowel cancer and have an 80 per cent lifetime chance of developing the condition. Those with FAP have multiple polyps inside their colon, which almost inevitably become cancerous at some stage (often before the age of 40) unless a careful watch is kept on them and suspicious polyps removed before they become cancerous. Frequently these people are advised to have at least a partial removal of their colon to reduce the chance of them developing cancer.

In addition to these inherited syndromes, close relatives of people diagnosed with bowel cancer are at increased risk of developing the problem themselves. The degree of risk increases with the number and closeness of the relatives affected. For instance, someone with one first degree relative (ie mother, father, brother or sister) diagnosed with bowel cancer under the age of 45, or with two or more first-degree relatives with this cancer diagnosed after this age will be at moderately increased risk of getting the same problem themselves. However, it is worth bearing in mind that it is such a common problem that ten per cent of people over the age of 50 will have an affected relative and those with a single relative diagnosed with bowel cancer over the age of 60 will have the same risk as the general population.

Another group of people who are at increased risk of bowel cancer are those with chronic inflammation of their bowel caused by conditions such as ulcerative colitis or Crohn's disease. These people are often kept under close surveillance with regular examinations of the bowel with a special telescope called a colonoscope.

Most bowel cancers result from cancerous change in polyps known as adenomas that develop in the lining of the bowel. As people get older they are more likely to develop bowel polyps so that eventually about 20 per cent of the population have them. The vast majority of these adenomas remain small and benign (non cancerous) but about 10 per cent of larger ones eventually become malignant usually after about 10 or 15 years. People with FAP develop multiple adenomatous polyps, sometimes hundreds of them, therefore the chance of one or more of these polyps becoming malignant at some stage are very high.

One of the problems with this condition is that the symptoms it causes can also be caused by other far less serious conditions. Also, especially in the early stages, bowel cancer may not cause any symptoms at all. This is one of the reasons why screening for the condition is a subject under regular discussion by the medical profession (see below).

Having said that, the main symptoms that should alert both the individual and their doctor to the possibility of bowel cancer are:

• A persistent change in bowel habit. For example, someone who normally only opens their bowels once a day will find their bowel habit changes to having to open their bowels several times a day and that this change persists for week after week. Equally, another person may find that they are suddenly going less often and that this alteration does not improve with time.
• Bleeding from the rectum, especially if it is persistent or keeps stopping and starting.
• Anaemia (a low blood count). In bowel cancer this is due to a small but regular blood loss that is passed in the faeces and may or may not be noticed as rectal bleeding.
• Abdominal pain. This may sometimes occur with bowel cancer although it is not a common symptom.
• A feeling of incomplete bowel emptying (known by doctors as 'tenesmus'). This is where the individual empties their bowels but even afterwards feels that there is still something in the rectum that needs passing. This is more common with rectal cancer ie cancer occurring just inside the back passage.
• Weight loss, which is a feature of many types of cancer including bowel cancer.
• Bowel obstruction (blockage). This happens when the cancer becomes large enough to significantly restrict the passage of matter through the colon or rectum. It usually results in persistent vomiting, abdominal distension and failure to pass faeces since these cannot get past the blockage.

The general practitioner (physician) who sees the individual may suspect bowel cancer either from the history (the group of symptoms described by the patient) or from the examination (if he or she can feel a lump in the abdomen or inside the rectum), or by the existence of a certain type of anaemia. The physician may order additional tests such as analysis of the motions (the faeces) for blood with a chemical test or may arrange for certain blood tests. However, other conditions can result in similar symptoms and examination and test findings, so diagnosis requires referral for further investigation.

The best investigation to diagnose bowel cancer is something called 'colonoscopy' which involves the examination of the inside of the colon with a special flexible telescope that allows the examining doctor to get a very good view of the lower bowel. The patient is usually given instructions in the days leading up to this test to ensure that their bowel is empty to enable the colonoscopy to be unobstructed by faeces. Biopsies (small pieces of tissue) can also be taken through the colonoscope and these can then be analysed under the microscope.

An alternative test exists called a double-contrast barium enema that consists of the insertion of a special dye (a liquid barium compound) into the rectum. The patient is then tilted on the x-ray table so that the dye spreads throughout the colon and air is then blown into the lower bowel. This results in the bowel wall being outlined on subsequent x-ray pictures so that abnormalities will show up. However, this does not allow biopsies to be taken is usually the preferred method of investigation for bowel cancer.

If bowel cancer is diagnosed, further tests may be done in order to 'stage' the cancer. This basically means finding out how far, if at all, the cancer has spread and is important both because it affects the treatment that will be recommended and the outlook (prognosis) for the patient. These tests may consist of ultrasound, CT (computerised tomography) and/or MRI (magnetic resonance imaging) scans of the abdomen. These scans include the liver since this organ is a common place for the cancer to spread to. Occasionally blood tests are done to assist in the staging process including tests for so-called 'tumour markers' which are chemicals within the blood which increase as the cancer spreads. The main tumour marker for bowel cancer is one called CEA.

Surgery is the usual treatment for bowel cancer. Although several different types of operation exist depending on where in the bowel the tumour exists, the basis for all of them is the same, which is to remove the tumour and sometimes the lymph nodes draining that part of the bowel.

Therefore, if the cancer is in the first part of the large bowel an operation called a right hemicolectomy is performed to remove the first half of the colon. If the tumour is in the second half of the colon a left hemicolectomy is performed and a sigmoid colectomy is done for cancer in the last part of the colon called the sigmoid colon. If the cancer is situated even further along in the bowel in the lower sigmoid colon or the upper part of the rectum an operation called an anterior resection is done whereas for those cancers that are low down in the rectum, ie just inside the anus, an operation called an abdomino-perineal resection (AP resection) is done.

Apart from the last of these, a permanent colostomy (where the bowel opens through a specially constructed opening in the abdominal wall) is not usually required. However, sometimes a temporary colostomy is formed to allow the bowel to heal up properly before re-joining it at a later date by removing the colostomy and allowing the faeces to go back through the normal route via the rectum and anus. Since an AP resection actually removes the rectum and anus, a permanent colostomy is essential in these cases.

• Radiotherapy (x-ray treatment) is sometimes given both before and after surgery since it has been found to reduce the chances of the cancer returning in the area from where it was removed and radiotherapy given before surgery has been shown to reduce death rates in some cases. However, it is not without its hazards and side effects such as inflammation of the bowel. Radiotherapy is also used in cases where the cancer has returned in order to reduce the symptoms caused by the cancer rather than to try to cure it. This is called 'palliative radiotherapy' since it is for symptom control rather than to eradicate the disease.
• Chemotherapy uses strong cancer-killing drugs and is often used after surgery for bowel cancer since it has been shown to improve the survival rate of this condition. The most common drug used is one called 5 FU that is given by infusion into the veins. Obviously, as chemotherapeutic drugs are powerful, they can cause side effects such as nausea and hair loss.

Patients who have had treatment for bowel cancer will generally be followed up both by the surgeon who performed the operation and by a specialist called an oncologist who is in charge of all the non-surgical treatment such as the chemotherapy or radiotherapy. Both specialists will arrange for the patient to be seen in outpatients for review, with the aim of looking for signs of recurrence of the cancer so that, if it occurs, it can be treated as early as possible.

The monitoring generally takes the form of asking the patient if they have any symptoms, examining them and then occasionally organising further tests. Such tests might include regular colonoscopies, scans, blood tests (usually including the measurement of the level of CEA, the tumour marker) and tests for liver function. If a recurrence of the cancer is found it may be treatable either with further chemotherapy or, in cases of single deposits within the liver, by removing the deposit surgically. However, return of the cancer is not always treatable in this way in which case there are many methods of controlling the disease and the symptoms it causes (so-called palliative treatment).

There are several particular areas of research into the treatment of bowel cancer. The first is called 'immunotherapy' which is the use of the immune system within the body to attack the cancer cells in a similar way to the method used by the body to protect itself from invading infections.

There are a number of ways in which immunotherapy may in future be used in the treatment of bowel cancer. For instance one method may be to vaccinate the body with a substance that would help it to make antibodies to the cancer cells in the same way that vaccines are used to make antibodies to infections such as measles. Another way involves the injection of so-called monoclonal antibodies into the blood.

Another area of research is into what is called gene therapy. Since there is often an inherited tendency for an individual to develop bowel cancer it may be possible to identify the defective gene carrying the 'blueprint' for colon cancer and in some way alter the gene to prevent the cancer from occurring or to slow its development.

There is also work being done into a new class of drugs called matrix metalloproteinase inhibitors which may slow down the growth of the cancer by blocking certain chemicals that the cancer needs for its growth.

There are several tests that can be used to screen people for bowel cancer but the question that has been under discussion by the medical profession for some time is who should be screened and with which test. The reason for this dilemma is that so far no test has been found to be simple, safe and accurate enough to screen the general population. Those considered to be at high risk of developing the condition generally have regular colonoscopies.

A simple test called a 'faecal occult blood' test exists which chemically tests for blood in the faeces and can find blood even if it is not visible to the naked eye. However, even though this is safe and easy to perform it is not particularly accurate insofar as it can be positive for blood in cases where the blood is from an innocent cause such as piles and can be negative in cases of bowel cancer. However, there is some evidence that this test may be useful in detecting bowel cancer early and therefore improving the outlook for some sufferers.

More involved tests such as colonoscopy or sigmoidoscopy (where a special telescope is inserted into the lower part of the colon) are more accurate but have rare but potential hazards such as the risk of bowel perforation and can be uncomfortable for the patient. However, despite this, colonoscopy is usually the screening test of choice for those at high risk of developing bowel cancer (see above).