Last update: June 2017

 

Incidence of bowel cancer

After lung cancer, bowel cancer is the most common cause of death due to cancer in Australia, with 17,000 new cases and 4,500 deaths each year. (The number of deaths from prostate cancer in males and breast cancer in females is actually higher than that for bowel cancer but because they both only affect roughly half the population, they cause less actual deaths.) Bowel cancer causes 14 per cent of all cancer burden of disease. It is thus a cancer that all people need to make a special effort to prevent.

As can be seen from the graph below, bowel cancer incidence increases with age and is more common in men. (Men have a lifetime incidence of about 1 in 19 and women a lifetime incidence of 1 in 28.)

The symptoms of bowel cancer often appear (or are identified) relatively late in the disease and at present only 40 per cent of patients diagnosed with colon cancer are diagnosed early enough to be offered a good chance of cure.

This means that the two prevention strategies available, dietary prevention and screening using faecal occult blood testing, are important health priorities for all adult Australians to consider.

When to talk about bowel cancer prevention with your GP: While most people can start screening for bowel cancer at age 50 years, some people are at greater risk and require earlier screening. For this reason, all people over the age of 30 need to talk to their doctor about when it is appropriate for them to commence screening.

Bowel cancer graph 1

Source: AIHW: Cancer in Australia 2000.
http://www.aihw.gov.au/publications/can/ca00/ca00-x02.pdf

Illness from bowel cancer is lessening: Happily, the actual death rate from bowel cancer has been decreasing over the past 20 years, from 31.8 per 100,000 population in 1986 to 19.6 per 100,000 in 2004, a drop of 38%. Over the same period there has been a drop in the mortality to incidence ratio of about 27%, from 0.51 to 0.37. (This means that in 1986, for every 100 cases of colon cancer found, there were 51 deaths from the disease; whereas in 2004 there were only 37 deaths for every 100 cases found.)

These improved outcomes are primarily due to greater public awareness of disease symptoms and increased screening for the disease, leading to cases being found and treated earlier; thus allowing more cures. Reduced smoking levels and better diet are also likely contributing factors. Luckily there is scope for all these contributing factors to be improved further and this will hopefullly translate into a significant decrease in the overall mortality from this disease in the future.

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What is bowel cancer?

All bowel cancers originate from a cell lining the large bowel wall that has undergone genetic changes, usually between three and twelve in number, that cause it to become pre-cancerous. The great majority of these genetic changes are thought to be due to environmental factors, with inheritance playing a prominant role in only about 10 per cent of cases. (Hereditary bowel cancer is discussed at the end of this chapter.)

This changed cell forms a small pre-cancerou growth called a bowel polyp. Further gene change causes these small polyps to form actual cancers. This whole process usually (but not always) occurs quite slowly and it is thought that it commonly takes at least 10 years for the initial changed cell to develop into an actual cancer. (Removal of the evolving polyp during this period prevents the cancer from developing.) While not all polyps will turn into cancers, the vast majority of cancers do develop from polyps and their presence significantly increases the risk of bowel cancer developing.

Most of these polyps (and thus cancers) occur in the second half of the large bowel and they are especially common in the sigmoid colon and the rectum. (Quite a number of cancers in the rectum are close enough to the anus to be felt by a doctor when doing a digital (finger) examination of the back passage.) Cancer rarely occurs in the small bowel.

The incidence of bowel cancer increases with age, with most cancers occurring in people over the age of 50. The average age at diagnosis is 70 years. However, cancers can occur in people as young as 20, so it is important for all adults to report symptoms that could indicate bowel cancer to their doctor. (A symptom list appears at the end of this section.)

Risk of getting bowel cancer according to age for men and women not at increased risk

Age

In the next 5 years

In the next 10 years

30 years

1 in 7,000

1 in 2,000

40 years

1 in 1,200

1 in 400

50 years

1 in 300

1 in 100

60 years

1 in 100

1 in 50

70 years

1 in 65

1 in 30

80 years

 1 in 50

 1 in 25

Source: National bowel cancer screening flip chart document.

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Reducing the risk of dying from bowel cancer

There are three ways a person can reduce their risk of dying from bowel cancer. They are:

1. Reducing the risk of developing bowel cancer

There is overwhelming evidence that the majority of bowel cancers occur due to environment factors and that these factors are mostly dietary in origin. A better diet and healthier lifestyle, including adequate physical activity, can reduce the risk of colon cancer by up to 65 per cent (and much illness due to many other important diseases). Such a reduction would make a huge difference to the burden of disease bowel cancer causes and for this reason everyone should consider adopting these measures. It is important to note that, while adopting these recommendations at any age is advantageous, most advantage will be gained by people who maintain them from childhood onwards. Teaching children to eat well and be physically active provides a huge lifetime health benefit and the best way to do this is be a good example. This topic is discussed in greater detail below.

Smoking is thought to be responsible for about 12 per cent of colorectal cancer in Australia and for smokers, this is another good reason to quit. Some readers will have heard it reported that long-term low dose aspirin therapy is also thought to be protective against colorectal cancer. While this may be the case, the side effects of such therapy are thought to significantly outweigh any advantage and its use is not recommended. Maintaining a healthy alcohol consumption also has a beneficial effect.


2. Screening for polyps (pre-cancerous lesions) and early cancers using faecal occult blood testing (FOBT). 


It is predicted that widespread adoption of screening for bowel cancer in Australia would be able to reduce bowel cancer deaths by up to 30%. FOBT often finds cancers relatively early and these early cancers have a 90 per cent cure rate. 
Despite very good evidence of significant benefit, the adoption of FOBT has to date (2017) only been modest.

3. Reporting symptoms

Recognising and reporting symptoms that may indicate bowel cancer can also aid in early diagnosis and cure. (These symptoms are listed at the end of this section.)

These three ways of reducing bowel cancer risk will now be examined in detail.

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1. Reducing risk factors for developing bowel cancer

Environmental factors

Many environmental factors have been implicated in causing bowel cancer. For some factors, including physical inactivity, obesity and inadequate vegetable intake, there is very good evidence to support these claims. For others, the evidence is too weak or inadequate to make any recommendation.

Associations with good evidence

  • Physical inactivity increases bowel cancer risk
  • Being overweight increases bowel cancer risk
  • Maintaining a healthy alcohol consumption (two standard drinks or less per day with two alcohol-free days per week) or not consuming any alcohol reduces bowel cancer risk
  • Smoking increases bowel cancer risk

Associations with moderate evidence

  • Consuming a diet high in fibre decreases bowel cancer risk
  • Eating five servings of vegetables per day decreases bowel cancer risk. (Cruciferous vegetables such as broccoli are best.)

Associations with weak or inconclusive evidence

  • The consumption of red meat, especially processed meat, increases bowel cancer risk
  • The consumption of charred food increases bowel cancer risk
  • A diet high in resistant starch decreases bowel cancer risk
  • Ensuring a calcium intake of 1000mg per day in adults decreases bowel cancer risk
  • Increasing selenium intake through dietary supplements decreases bowel cancer risk
  • Increasing folate intake decreases bowel cancer risk

While there is insufficient evidence to make definite recommendations regarding many possible cancer reducing compounds / elements, it needs to be stressed that investigating the influence of foods and nutrients on diseases is very difficult and associations that exist may take many years to show up. This may result in some actual preventative influences never being proved. Many people are keen to adopt natural preventative measures and as long as their adoption can be part of a healthy diet, there is no harm in doing this. If, however, their adoption means going outside a healthy diet e.g. taking supplements, then they are best avoided and the NHMRC in their publication Clinical Practice Guidelines for the Prevention, Early Detection and Management of Colorectal Cancer (2005) actually recommend that people do not use multivitamin supplements for the purpose of reducing colorectal cancer risk.

The following discussion of risk factors is adapted from information contained in the NHMRC publication mentioned above.

The World Health Organisation believes that about 16 percent of colon cancers can be attributed to physical inactivity. To gain maximum benefit regarding reducing colon cancer risk, a person needs to do 30 to 60 minutes of moderate to vigorous exercise per day. This can produce a 30 to 40 per cent reduction in colon cancer risk compared with inactive people. The reason for the benefit is unclear but it may be due to improvements in the body's immune function or a reduction in the time it takes food / faeces to transit through the bowel. (A reduction in 'transit time' reduces the length of time the bowel wall is exposed to ingested carner causing substances.)

About 11 per cent of colorectal cancers in Australia are thought to be due to obesity. This is another good reason to maintain a healthy weight. Not surprisingly it has also been found that a high dietary energy intake, which is a major cause of obesity, is related to colorectal cancer.
Some studies have also implicated a high dietary fat content in causing colorectal cancer although the evidence for this is weak. (A healthy diet should restrict dietary fat to about 25 to 30 per cent of total energy intake.)

Alcohol consumption is associated with a moderate increase in the risk of developing bowel cancer. This association may be slightly less with wine, particularly in women. To minimize this risk, it is recommended that men keep their intake to no more than two standard drinks per day and women to no more than one standard drink per day. (To help reduce the risk of addiction occurring health authorities recommend that all adults who consume alcohol should have two alcohol-free days per week.)

Smoking is thought to be responsible for about 12 per cent of colorectal cancer in Australia and for smokers, this is another good reason to quit.

There is some debate regarding the beneficial effect of dietary fibre in reducing bowel cancer. One reason for this is that it is difficult to interpret evidence on this topic because the good studies on this topic were not done over a sufficiently long period to show any effect. (It is likely that the effect of increasing dietary fibre on bowel cancer takes many years to occur.) However, it is generally felt that a high fibre diet, particularly one with a high content of insoluble fibre, (see section on dietary fibre) will probably cause a reduction in the risk of developing colorectal cancer.

Numerous studies have examined the effect of vegetable intake on cancer and have found that vegetables are quite likely to be protective against cancers of the upper gastrointestinal tract (e.g. cancers of the stomach and oesophagus).  However, more recent evidence has cast some doubt on the once widely held view that vegetable intake is protective against colorectal cancer and it is now thought that this is more possible rather than probable. The evidence is better but still not definite for cruciferous vegetables, which include bok choy, broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collards, kohlrabi, mustard greens, swedes and turnips. These vegetables contain indoles and isothiocynates, which are sulphur-containing compounds that are known to be protective against colorectal cancer. All these vegetables are also high in fibre and anti-oxidants. A wide variety of vegetables (and fruit) is likely to give the best protection.

Red meat, particularly processed meat such as salami, has been implicated in causing cancer, particularly gastrointestinal tract cancers and the well-respected 2007 World Cancer Research Fund Report recommends consuming less than 500g of red meat per week. (The complete recommendations of this report are in the section Cancer Prevention - General concepts.) An appropriate serving size is about 80g, which is a piece of meat about the size of a pack of playing cards). Processed meats, including meats that are smoked, cured or salted can be eaten occasionally but ideally should not form a regular part of the diet.

Charred food, including meat, toast and vegetables, can create chemicals that increase the risk of cancer, particularly bowel cancer. These chemicals include polynuclear aromatic hydrocarbons and heterocyclic amines. Polynuclear aromatic hydrocarbons are absorbed by foods when they are smoked (especially fatty meats) or are produced by charring foods. High temperature cooking (frying, grilling and barbequing) of meats and fish turns some protein compounds into heterocyclic hydrocarbons, which are weakly carcinogenic.
The evidence that these chemicals cause cancer is inconclusive. However, it is probably reasonable to moderate their intake by cooking using low heat methods such as steaming, micro-waving or stewing and cooking over the hot-plate rather than over coals when barbequing. Also, micro-waving the meat briefly first reduces the creatine content that gives rise to heterocyclic amines.
Try using marinades to add extra flavour rather than charring food. (Avoid too much soy sauce as it has a very high salt content, even in the low-salt variety.)

Most starch is broken down in the small intestine. Resistant starch is starch that is not broken down in the small intestine and therefore reaches the large bowel, where it is broken down by bacteria. As it breaks down, it generates beneficial substances, especially butyrate, that help keep bowel cells healthy and reduce the chances of cancer causing chemicals contained in food (carcinogens) adversely affecting bowel cells. Resistant starch also acts to increase faecal bulk, which dilutes carcinogens, encourages the growth of healthy bacteria, and reduces the growth of unhealthy bacteria.
The evidence base for resistant starch benefit is weak and its use is therefore not officially recommended. To be of any benefit, it is thought at least 20g a day is needed. Hi-maize contributes a small amount of resistant starch to the diet and is found in some breads, breakfast cereals and muffins. Wholegrain cereals, rice, pasta (when eaten firm i.e. not over-cooked), legumes, slightly unripe bananas and potato also contribute.

There is conflicting evidence regarding the effect of calcium on bowel cancer and no definite recommendation can be made. However, an intake of over 1000mg is important for all adults to help prevent osteoporosis, with any beneficial effect on colorectal cancer being an additional advantage. Calcium’spossible effect in reducing bowel cancer is thought to be due to a reduction in bile acids and fatty acids in the colon. There is no evidence that consuming a greater calcium intake through calcium supplements is of any benefit.

While several studies have suggested that increasing folate intake in the diet reduces colorectal cancer, the evidence is still too weak to make a recommendation. Folate may reduce cancers, including bowel cancers, by helping to repair damaged DNA (genes) in cells that might otherwise become cancerous. It can be obtained from leaf vegetables, spinach, asparagus, baked beans, citrus fruits and folate enriched breakfast cereals and breads. (Overcooking vegetables significantly reduces their folate content.)

Selenium is an essential trace element that everyone must have in their diet but requires only in very small quantities. There is some evidence that increasing the daily dose via supplements may reduce the incidence of colorectal cancer, although the evidence is at present weak. This effect is thought to occur through reducing oxidative damage to the DNA (genes) of cells, which it achieves via its role as part of an enzyme that helps remove hydrogen peroxide from the cell. Such oxidative damage can lead to cancerous changes in the cell. Selenium may also help improve immune function in the body. Selenium is found in grains, vegetables, brazil nuts, fish and meat. The amount of selenium in grains depends on the soil content of selenium in which they were grown. Australian soils are generally adequate in selenium.

Several studies have found a significant reduction in bowel cancer incidence in people on low-dose long-term aspirin. It takes about three years of treatment for this effect to start occurring and the benefit increases to a sustained maximum level after about five years of treatment. The effect is equal for men and women. Interestingly aspirin has also been found to decrease the spread of cancer that is already present via the blood (i.e. metastises developing).

For the general population who are not at increased risk of developing heart attacks, strokes or bowel cancer, there is still no general consensus in the medical community that potential benefits associated with aspirin use, primarily from cancer reduction and reduction in heart disease, outweigh increased risks from bleeding and long-term low-dose aspirin is not currently recommended.

Long-term aspirin therapy is associated with significant side effects, including gastrointestinal bleeding which can occasionally be life-threatening. Such bleeding usually occurs within the first five years of low-dose aspirin therapy. After that, there is little increase in risk of it occurring. (Most bleeding occurs relatively soon after the commencement of treatment because these patients have another factor present that increases the risk of bleeding occurring when taking aspirin.) Some people are also suffer significant allergic reactions to aspirin.

Aspirin also reduces the risk of developing other cancers, mainly oesophageal and stomach cancer.

Obviously, any potential benefit would be greater in people in their fifties and sixties as they have longer to live than someone in say their late seventies. The benefit would also be likely to be greater in people with an increased risk of bowel cancer due to having a family history of this disease.

There is also evidence that the benefit gained is much greater for people with a specific type of inherited bowel cancer, Hereditary non-polyposis colorectal cancer (HNPCC) or Lynch Syndrome. For people with this condition, the use of long term low dose aspirin is likely to be recommended in the not-too distant future. The best dose of aspirin for these people is still being evaluated. (This is a devoping issue and people with this condition should ask their doctor about current recommendations.) Interestingly, about 15% of the 'normal' population have bowel cancers that develop in a similar way to this inherited form and thus would also be likely to benefit from long term aspirin therapy. The problem is that their is no way of telling who they are prior to them developing a cancer. (See section on Genetic testing for inherited causes of bowel cancer.)

Salicylate, the active ingredient in aspirin, is contained in numerous foods and these foods are also likely to be of benefit in reduceing gut tumours, including stomach, oesophageal cancer and colorectal cancer. Salicylte containing foods include fruit (dried fruit, cherries, pineapple oranges, rockmelon, strawberries, apples), vegetables (gherkins, mushrooms, capsicums, zucchini, egg plant and green beans), condiments (thyme and oregano) and some beverages. Some people are sensitive to salicylates.

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National Health and Medical Research Council dietary recommendations for reducing bowel cancer risk

Below is a summary of the dietary and lifestyle recommendations produced by the NHMRC for reducing bowel cancer.

  1. Eat at least five portions of vegetables per day. A portion of vegetables weighs 60 to 90 g.
  2. Eat a high fibre diet, especially insoluble fibre.
  3. Reduce dietary fat intake to 25 per cent of total energy intake and avoiding large amounts of animal fat.
  4. Maintain a normal weight.
  5. Avoid smoking.
  6. Partake in regular physical exercise.

 

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2. Screening for bowel cancer

Screening for bowel cancer is an effective way of reducing the risk of dying from bowel cancer and is the most beneficial of all the cancer screening tests available at present. There are several methods of screening and the method that is most appropriate for an individual will depend on their underlying risk of developing the disease.

Sorting out a screening plan: All adult patients need a bowel cancer screening plan and this needs to be determined well before the age of 50 (at say 30 years of age) as people at high risk need to commence screening well before they reach 50 years.

Screening people at normal risk of bowel cancer with faecal occult blood testing (FOBT)

Ninety-eight per cent of the population is at normal risk of developing bowel cancer and 85 per cent of bowel cancers arise in this ‘normal risk’ population. Thus, the success of a screening program aiming at reducing bowel cancer incidence in Australia will depend on the participation rate amongst this group.

People at normal risk of bowel cancer are those who:

The screening test that has been shown to be of benefit to normal risk people by reducing bowel cancer deaths is faecal occult blood testing (FOBT).

The evidence supporting the benefits of bowel cancer screening using FOBT is better than that for any other cancer screening proramme, with three large very good trials showing a reduction in death rate of about 30% for those participating in at least second yearly screening from the age of 50.

How does faecal occult blood testing (FOBT) work?

Bowel cancers and pre-cancerous bowel polyps often bleed. This bleeding is often only slight and thus difficult to see with the naked eye when looking at bowel motions. Testing for minute amounts of blood in the faeces, which is what FOBT does, can help detect these otherwise silent cancerous and pre-cancerous polyps. This often allows lesions to be found early on, before they have spread to other parts of the body. (Finding bowel cancers early allows a 90 per cent cure rate.)

Australian Government health authorities have recently recommended that all the ‘normal risk’ population should be offered screening for bowel cancer from the age of 50 years. They have suggested that this screening should be done every two years. It needs to be done this often because bowel polyps and early cancers often bleed intermittently and thus lesions are not always detected with FOBT. Repeated testing allows the best chance of finding the lesion.

Early on in the screening program there was a problem with some FOB testing kits due to heat damage which meant that the results were unreliable and thus a large number of tests needed to be repeated. This problem has now been corrected.

Types of faecal Occult Blood Testing

There are two main types of faecal occult blood screening tests available.

Immunochemical FOBTs: This type of test is the test that is used for the Government screening programme. It usually involves poking a bowel motion (in the toilet bowl) with a test stick. The test needs to be done twice on two consecutive days and is then posted to a laboratory to be checked for the presence of blood. No medical and dietary restrictions are required prior to collection. The test kit costs about $40, which includes the cost of testing. (Recent problems with the test kit (in 2009) have now been overcome.)

Older tests: This FOBT involves collecting three small specimens of bowel motions at home on different occasions, smearing them onto a slide, and sending them to a laboratory to be checked for the presence of blood. This test requires medical and dietary restrictions prior to collection. Most people do not like doing this test and it is not as accurate as the immunochemical tests. Thus it is now not usually recommended. These older tests are not recommended for use in the Government screening programme.

What are the benefits of screening using faecal occult blood testing?

There is good evidence that, if all Australian adults over 55 years of age have faecal occult blood testing (FOBT) every two years until they reach 70, deaths from colorectal cancer could be reduced by at least 30 per cent (and perhaps up to 40 per cent). An FOBT screening program with high community participation levels would be expected to decrease death from bowel cancer in the community by at least 25 per cent and actual bowel cancer incidence by up to 20 per cent. (This reduced incidence occurs because pre-cancerous polyps that may have later turned into bowel cancers will be found and removed during the colonoscopy investigation of people with positive FOBTs.)

Which age groups benefit from FOBT screening?

There is good evidence that second yearly FOBT screening benefits most people from ages 50 years to 75 years.

Screening this many people is a huge logistical undertaking and thus the Government promoted screening campaign is initially only targeting people aged 50 to 65 years. However, future campaigns will probably aim at a wider age group; people aged 55 years to 74 years.

Also, the Government promoted campaign does not yet fully adhere to the best practice national guidelines and thus people may need to consider having FOBT screening more often than the Government program recommends. Thus it is best to discuss with your GP what is the best program for you.

As with all cancer screening, these substantial benefits apply to the group tested not the individual and most individuals who undertake screening will gain no benefit. (It is just that those that do benefit may well have their life saved!!)

Unfortunately, at present less than half of those eligible for the current (limited) screening program are electing to have the test.

Results of FOBT screening tests

The results for screening using FOBTs are shown in the boxed section below. They are shown as the overall outcomes from having second-yearly tests over a 10 year period; that is, the results from having 5 tests done To summarise, the approximate expected results are as follows:

A single test will pick up about 27 percent of all cancers and about 66 per cent of invasive cancers. These figures rise considerably if two or more specimens are tested over two to three days, with up to 80 per cent of cancers being able to be detected under ideal conditions. The Australian screening program recommends that two tests should be done on consecutive days. (This means that 20% to 30% of cancers are NOT picked up by screening and thus people who have had a recent negative FOBT should not ignore bowel cancer symptoms. These symptoms are listed at the end of this section.)

All positive tests need further investigation.

10 year outcomes for people screened and non-screened for bowel cancer using FOBT

 

Results for 1000 people for the 10 years from age 50 to 60

(in number of cases)

Results for 1000 people for the 10 years from age 60 to 70

(in number of cases)

 

Have biennial screening

DO NOT have any screening

Have biennial screening

DO NOT have any screening

False positive tests 1

263

0

252

0

People who get colorectal cancer

7

8

15

20

Cancers detected 2

By screening

Interval cancers 3

6

Up to 8

13

Up to 20

3

7

3

6

Cancers missed by screening

(False negative tests)

1

Not applicable

2

Not applicable

Number of people who may die from colorectal cancer 4

2

2

5

7

Extra pre-cancerous lesions (large polyps) found by screening

7

0

18

0

Notes:

  1. Most but not all of those with a positive FOBT will require investigation with colonoscopy. The people with a false positive FOBT are those in whom such investigation finds no cancer and no large polyp. 
  2. The difference in the possible numbers of cancers between the screened and not-screened groups occurs because investigation of abnormal screening FOBTs by colonoscopy will involve the removal of lesions (i.e. large polyps) that may later have changed into cancers. Thus, less actual cancers will occur in the screened group.  
  3. Interval cancers are cancers that are detected between screening tests. That is, they are not detected through screening.
  4. These people have colorectal cancer that will kill them in time. The reason the term ‘may die’ is used is that there is no guarantee that another illness will not cause their death beforehand.

Source: AD June 2, 2006 pp 25 – 32; How to Treat.  Informing patients about screening by Dr Lyndal Trevena

 

What does a positive FOBT mean?

A positive FOBT with either type of test just means that blood was found in the faeces and that this requires further investigation. There are many causes for blood in the faeces and most people with a positive test will not have bowel cancer. However, the likelihood of having a cancer is roughly 12 to 40 times greater in someone who has a positive faecal occult blood test.

It goes without saying that there is no point having a FOBT if the person is not going to have a positive test investigated!!!! For those that do turn out have cancer, FOBT often finds them relatively early enabling a curative treatment. Seeking medical attention as soon as possible after a positive FOBT provides the best chance of curative treatment. Do not delay the investigation of a positive test.

Almost all people with a positive test will need to have a colonoscopy to exclude cancer or polyps as a cause for the blood found in their bowel motions. About one in twenty colonoscopies following a positive FOBT find a cancer. (Colonoscopies done in people without symptoms or a positive FOBT only find cancers in one in 500 cases, indicating that FOBT is a very good screening tool.)

Even if initial examination of the person finds another possible cause for the positive FOBT, such as haemorrhoids, a colonoscopy examination should still be carried out to make sure a cancer is not missed. Colonoscopies can be done in the private sector for those who have private health insurance or in public hospitals for those without insurance.  

The introduction of screening for bowel cancer has increased significantly the coloscopy workload and has meant that there is likely to be a significant delay before colonoscopies can be done on many people with a positive test. This is unfortunate as it will mean some people will suffer significant anxiety whilst waiting for a test. Governments in Australia are aware of this problem and are in the process of increasing the availability of colonoscopy services.

Disadvantages of FOBT

False positive and negative tests are a problem with FOBT. Not all colon cancers bleed and for this reason, some individuals with colorectal cancer will have a negative test. The percentage of cancers missed also depends on the type of tests with newer tests being able to pick up between 70 and 80 per cent of cancers present at the time of testing.

Whenever a FOBT is done, around three to five per cent of the general population will have a false positive test. This means that about 50% of those people who elect to have screening for 20 years (i.e. 10 screening tests) will endure unnecessary worry and an unnecessary procedure to exclude the cancer. This procedure is almost always a colonoscopy, which very occasionally has significant complications.

Also, in some areas there are already delays in accessing ‘public colonoscopies’ and this situation is likely to get worse with the increased need for colonoscopies that the adoption of a screening program will create. (The program commenced in mid 2006.) Some individuals may unfortunately have an anxious wait.

Compliance was a problem with older tests as people had to obtain samples of faeces. This is less of a problem with newer tests as they only require obtaining a sample of toilet water.

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Other screening techniques for bowel cancer - Sigmoidoscopy, colonoscopy, CT scaning.

FOBT with flexible sigmoidoscopy screening
Flexible sigmoidoscopy can be offered as a screening procedure for individuals at normal risk of bowel cancer in addition to FOBT. This combination can be expected to pick up about 75 per cent of cancers, although few studies have examined the effectiveness of this combination as a screening technique.
In this examination, a tube is inserted through the anus to examine the rectum and the last part of the bowel (the sigmoid colon) for cancers. By itself, it can be expected to pick up about 50 per cent of bowel caners as about half of all bowel cancers occur in this area. Its main drawback is that it cannot disclose the other 50 per cent of cancers that are higher up in the bowel. For this reason, it must be done in conjunction with FOBT.
Flexible sigmoidoscopy is done in a doctor’s surgery, is perhaps a bit uncomfortable but generally not painful, and does not require an aesthetic. If used for the purposes of screening for bowel cancer, it should probably be done roughly every five years.

‘Virtual colonoscopy’ using a CT scanner.
This technique has received much media attention in recent years. It is non invasive but does give a large dose of radiation and this may be a problem as the test would need to be done at regular intervals if it was used for screening purposes. It unfortunately misses quite a number of smaller lesions and it is relatively expensive. Thus, it is not recommended for screening in Australia.

Barium Enemas
This older X-ray technique has problems with missing too many smaller lesions, especially compared to newer procedures such as colonoscopy; and, unlike colonoscopy, smaller lesions can not be removed at the time of the procedure. It is also not recommended for use in screening.

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Screening individuals at moderate and high using colonoscopy

Only two per cent of the population is at a significantly increased risk of bowel cancer. These people require more thorough screening, which should be done by colonoscopy. (Some screening used to be done with a special X-ray called a barium enema. Barium enemas are not used now as they only detect about 40 per cent of the polyps that are found with colonoscopy.) The frequency of colonoscopy screening depends on the person’s risk level and all patients with an increased risk of bowel cancer need to discuss their screening program with their medical practitioner.

It is important to realise that finding and removing a polyp changes the requirement for future colonoscopy screening is required and that the patient needs to follow the advice they are given regarding the frequency of colonoscopy follow up.

Colonoscopy

A colonoscopy is an examination of the large bowel using a fibre-optic, snake-like instrument that is inserted via the anus. The investigation is done under anaesthetic.

The main advantages of colonoscopy are that almost all lesions can be found as it examines all parts of the large bowel and the majority of lesions (polyps) are small enough to be removed at the same time. Also, there are no false positive tests and false negative tests are very uncommon.

The principle disadvantage is that the procedure is rarely associated with significant complications, such as bowel perforation. These mostly occur where a polyp needs to be removed and when this is done:

  • the risk (with a skilled surgeon) of significant bleeding requiring transfusion to replace blood loss is about one in 500 procedures. (Bleeding mostly occurs when the removal of a polyp is required.)
  • the risk of bowel perforation is about one in 1,500.
  • death may occur. (This is very rare, occurring in about one to two in 10,000 procedures).

It is not until the 55 to 60 year age group that the risk of dying from colorectal cancer is an order of magnitude greater than the risk of suffering a serious complication from colonoscopy. This is the main reason that colonoscopy is not used for screening normal risk individuals.

As the complication rate is to some extent related to the skills of the surgeon performing the test, it is important that patients choose a surgeon who performs colonoscopies regularly.

Another limitation is that in about 5 per cent of colonoscopies are not able to examine adequately the entire large bowel. This can occur because the surgeon is unable to pass the colonoscope through to the proximal end of the large bowel. It can also occur because inadequate bowel preparation has resulted in large amounts of faecal material remaining in the bowel and this can obscure the surgeon's view.

Further information and patient handouts about colonoscopies can be found in the Colorectal Surgical Society of Australasia web site: https://www.cssanz.org/patients or in the Gastroenterological Society of Australia web site http://www.gesa.org.au/professional.asp?cid=26&id=87

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Screening those at moderately increased risk

People at moderately increased risk of bowel cancer include:

These people need regular check ups with their doctor, FOBTs each year, and colonoscopy starting either at 50 years or when the person is ten years younger than earliest age that a family member was diagnosed with bowel cancer, which ever age is the youngest.

Screening those at high risk

Individuals in this group account for less than one per cent of the population and include:

 

Screening recommendations according to bowel cancer risk level

(for people not at high risk of bowel cancer)*

Family history of bowel cancer

Relative risk

Screening recommendations

No family history (Normal population risk)

Normal risk

FOBT every two years from age 50.

One first degree relative diagnosed after age 55 yrs

Twice normal risk

FOBT every two years from age 50 and consider sigmoidoscopy every 5 years from age 50.

One first degree relative diagnosed before age 55 yrs or two first or second degree relatives on one side of the family diagnosed at any age with bowel cancer

Three to six times normal risk

Colonoscopy every five years from age 50 and consider FOBT every year from age 50.

*This table does not apply to people with conditions that make them at high risk of delepoing bowel caner. (See list above). These people need individual advice regarding appropriate screening.

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Genetic testing for inherited causes of bowel cancer

Genetic testing for bowel cancer is usually done using a blood sample from someone in the family that definitely has the disease. Once a mutation is identified in that person, others in the family can be checked for the same mutation. (Testing is done from age 12 for FAP and age 18 for HNPCC.) The consequences of genetic testing are many and varied and often involve all family members, not just the person being tested. For example, what should other family members be told about the results? Would they want to know? For this reason, people requesting or needing genetic testing should be referred to a specialist in genetics or a genetic clinic for counselling prior to testing. Genetic testing is not perfect and some abnormalities can be missed. Thus a negative test does not guarantee the person is not affected.

Familial Adenomatous polyposis (FAP):

This condition is caused by a mutation (change) in a bowel cell gene (the APC gene). It is rare, affecting about one in 10,000 people. The changed gene causes many hundreds of polyps to grow in the bowel, a number of which will turn cancerous if left untreated. The polyps develop in late teens to early adulthood and cancer is likely by the age of 40.

As it is an autosomally dominant inherited genetic condition, there is a 50 per cent chance that a person will have this disease if a parent has it. Diagnosis by gene testing is now available for this condition. Such testing is first offered to an affected individual and if a gene abnormality is found, other family members can be tested if they desire. (If the gene is not present, bowel cancer risk is most likely to be normal but there is no definite guarantee. Remember genetic testing is not perfect.)

Hereditary non-polyposis colorectal cancer (HNPCC) or Lynch Syndrome

This condition is due the inheritance of an abnormality in a DNA mismatch repair gene. (These genes repair errors that are made when DNA is copied during cell division.) There are four such genes and a mutation in any one of them is associated with an increased lifetime risk of numerous types of cancers. (See table below.)

Increased cancer risk in people with Hereditary non-polyposis colorectal cancer (HNPCC) (Also called Lynch Syndrome.)

Cancer

Lifetime risk of developing cancer in people with HNPCC (Lynch Syndrome)

Lifetime risk in general population to age 85 years

Colorectal – Male

70 to 80%

5 to 6%

Colorectal – Female

40 to 50%

5 to 6%

Uterus (endometrial cancer)

40 to 50%

2 to 3%

Gastric

5 to 15%

1%

Ovarian

Up to 10%

1 to 2%

Brain

3 to 6%

0.6%

Urinary tract

3 to 4%

1%

Small bowel

1 to 5%

0.01%

Figures taken from an evidence-based cancer genetics resource available at the NSW Cancer Institute's website: https://www.cancerinstitute.org.au

 

Cancers associated with this condition arise from a polyp but there are not multiple polyps present as in FAP and so the problem is more difficult to diagnose. It should be suspected in families with:

Genetic testing can be done but it is not possible to identify all carriers yet.
This condition can appear at varying ages, but most commonly in 30- and 40-year olds and older age groups. However, it can appear in people in their twenties and even younger. Women over the age of 35 with this condition should have check ups for uterine, ovarian and other cancers as they have an increased risk of these cancers also.

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3. Recognising possible bowel caner symptoms

Reporting symptoms that may possibly indicate the presence of a bowel cancer as soon as they appear can also help detect early cancers and increase the likelihood that the disease can be cured.

Any of the following symptoms indicate that bowel cancer might be present. (It needs to be emphasised that they also occur in many other diseases and people with these symptoms will probably not be shown to have cancer. However, the person won’t know until he or she finds out!)

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Further information

Clinical Practice Guidelines for the Prevention, Early Detection and Management of Colorectal Cancer. National Health and Medical Research Council(2005)
An comprehensive up to date summary of the existing knowledge base regarding the reduction of bowel cancer risk in the Australian population.
www.nhmrc.gov.au/publications/subjects/clinical.htm
(Link is located on this page.)

Further information and patient handouts about colonoscopies can be found in the Colorectal Surgical Society of Australasia web site: https://www.cssanz.org/patients or in the Gastroenterological Society of Australia web site http://www.gesa.org.au/professional.asp?cid=26&id=87

The NSW Cancer Institute (For information about any cancer topic)
https://www.cancerinstitute.org.au

Sydney University Bowel cancer screening aids
http://sydney.edu.au/medicine/public-health/step/publications/decisionaids.php

 

 

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