Last partial update: June 2019 - Please read disclaimer before proceeding

 

What is cancer?

Most cancers orginate from genetic changes in a single cell. These changes commonly associated with these changes include the following:

The ability to grow more quickly, reproduce more rpaidly and the ability to live in various parts of the body are quite different attributes and to occur each probably requires different genetic changes in the cell. For a cell to become fully cancerous, it is thought that it needs to undergo between 5 and 10 specific genetic changes.

Numerous genes influence cancer occurrence in a cell and they are grouped as follows:

Gene mutations occur commonly; so why don't we all get cancer?

Gene mutations are a common occurrence and cancer would be much more common if all such changes automatically caused a cancerous change. However, this is not the case. The reasons are as follows:

Cancer usually takes time to occur: The likelihood of each such change occurring increases in proportion to the length of time the cell (and its progeny) are exposed to external influences that can cause such a change. (Once a cell develops a cancerous change in its genes it hands this change on to cells that arise from it when it divides, as do the next generation of cells and so on.) This whole process of cancerous change acculumulation usually takes many years and this is why most cancers are more common in older people.

It is important to note that most cancers originate in cells that started off being 'normal' and were gradually changed due to lifetime exposure to cancer causing factors. There is no inherited abnormality in such cells that contributes to cancer cell transformation and the relatives of people with these types of cancer do not have an increased risk of developing the cancer. That is, most people with a cancer do not pass on any increased risk of developing that cancer to their children and their relatives are not at increased risk of developing that cancer.

Inherited cancer:

The chromosomes (i.e. genetic material) in every cell of a person's body originate from the chromosomes (genetic material) in the sperm and the ovum which created their original embryo. The chromosomes (23 from the sperm and 23 from the egg) and the multitude of genes they possess are similar in the egg and the sperm and thus in each cell we get 23 similar pairs of chromosomes (not 46 completely unrelated chromosomes) and a multitude of similar pairs of genes in each cell (not a multitude of completely unrealted genes). (Body cells will not contain exactly the same genetic material as the original combined egg/sperm genetic material as external influences that the cells are exposed to while the person lives their life cause changes in this genetic material; but all cells will contain pairs of genes (alleles) that are very, very similar to the original egg/sperm genes.)

An inherited increased risk of cancer occurs when there is a deffective gene that in some way increases the risk of cancer ocurring in either the ovum or the sperm (or very rarely both). Unless the change was present in both the egg and the sperm (a rare occurrence), then the person will have one normal gene and one cancer-enhancing gene. As the gentic material in every cell originates from this original genetic information, every cell has faulty genes present in either the sperm or ovum. Such changes are relatively uncommon with less than 10% of cancers overall having some inherited cause.

As stated above, abnormalities contributing to a cell becoming cancerous often occur in tumor suppressor genes or in DNA repair genes and, in both these types of genes, both genes of the gene pair need to be affected for the cancerous influence on the cell to occur. The reason that many people with an inherited abnormality in one of these genes don't get cancer is that the functioning member of the gene pair continues to function normally.) An inherited defective tumor promotor gene does not require the other member to change and thus is potentially more serious; but much less common.

About 15% of prostate, breast and bowel cancers and melanomas tend to cluster in families. At present, nine genes that can transfer an increased risk of cancer between family members have been found. While these genes can be tested for, it is important that proper genetic counselling occurs beforehand so that the implications of finding a family genetic problem are fully understood. People with a family history of cancer should notify their doctor so its significance can be assessed. (Remember that in 85% of cancers, inheritance is not a significant causal factor.)

The most important inherited cancers are breast cancer and bowel cancer and more detailed information apears in the sections on these illnesses. Other important ones include ovarian and prostate cancer and melanoma.

Familial Adenomatous Polyposis - An example of cancer inheritance

This condition causes an increased risk of bowel cancer and is caused by an abnormality of a tumor repressor gene on chromosome 5. The affected person inherits one functioning allele and one non-functioning allele in each bowel wall cell. Over time an increasing number of bowel wall cells get mutations to the normal allele and this causes the cell to reproduce more quickly, resulting in a polyp forming. Often thousands of such polyps form. However, it requires other genes to be affected for one of these polyps to become cancerous. (Remember that cancer usually requires 5 to 10 mutations in the cell.) This does happen in most of the affected people and many will get bowel cancer from several polyps. People who inherit two normal alleles require both alleles to be mutated for polyps to start forming; a much, much less common occurrence.

How does cancer cause death?

Injury and death from cancer are due to damage to normal body tissue caused by ‘colonies’ of abnormal cancer tissue that are growing relatively quickly in size. This damage can occur where the cancer started or in other places in the body that some of the cancer cells have spread to. This spreading process is called metastasising and it is the damage caused by multiple colonies of 'metastatic' cancer cells in the body that causes most cancer deaths (about 85%).

 

Death and disability from cancer in Australia

Most of the burden of disease attributable to cancer comes from cancers that can to be prevented to a significant extent. The most important of these are breast, lung and colorectal cancers, which account for 47% of female cancer illness and 31% of male cancer illness. A large fall in the incidence of these common cancers will need to occur if there is to be a significant reduction in the premature loss of life from cancer in Australia. The incidence and years lost due to disability and death from these cancers are shown in the graphs below.

A couple of points worth noting from the graphs:

1.While there are relatively fewer deaths from melanoma, it is also important because it is a major cause of cancer in young people (especially males) and is almost always preventable. Other cancers that can be almost completely prevented include lip and cervical cancer.

2. While overall illness from breast cancer is still significantly greater than that from lung cancer, lung cancer has taken over from breast cancer as the commonest cause of cancer death in women. (This is a real tragedy as almost all lung cancer deaths can be prevented by not smoking.)

Healthy life options can have a huge effect on the reducing cancer deaths. Adhering to the recommendations made in these sections can reduce overall risk of death from serious cancers by well over 50 per cent, as can be seen in the table below.

Effect of cancer prevention initiatives

Initiative

Reduction in mortality

Better diet

30%

Better screening and early detection

25%

Avoiding smoking

20%

Overall reduction in cancer rate

Well over 50%

 

Source: Australian Institute of Health and Welfare: Australian Burden of Disease Study 2011

 

Source: Australian Institute of Health and Welfare: Australian Burden of Disease Study 2011

 

Helping prevent death from cancer

The two main ways to help prevent deaths from cancers are;

  1. Preventing cancer cells from developing in the first place; by far the best option.
  2. Medical interventions to help find and treat cancers before they become incurable by:
    • screening for cancers before symptoms develop (or are noticed)
    • identifying cancer symptoms early, thus hopefully enabling treatment to be initiated while the cancer can still be cured. (In most cancers, this requires finding the cancer before it has spread to other parts of the body (metastasized).)
    • effective treatment of advanced cancers

Each of these options will now be examined to see how cancer prevention can be best achieved.

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1. Preventing the creation of cancer cells in the body

As stated previously, cancers occur because changes in the genes of a single cell allow that cell to live longer and multiply more quickly than a normal cell. The actual mechanism is likely to be quite complicated and involve the interplay of numerous factors, such as a genetic predisposition to the cancer, exposure to cancer-causing substances (carcinogens) etc. While we know some causal factors in many important cancers (see boxed section), just how long a person needs to be exposed to these factors for cancerous change to occur is uncertain and varies for different carcinogens and different cancers (and for different people).

 

Some cancer causing factors / substances

Cancer caused

Cigarette smoke

Cancers of the lung, mouth, pharynx, larynx, bladder, kidney, oesophagus, stomach, cervix, vulva, penis, anus.

Asbestos

Outside lining of the lung (mesothelioma), lung and peritoneum

Sunlight (UV radiation)

Melanoma and other skin cancers

Lack of fruit and vegetables

Many cancers, including cancer of the bowel, stomach, lung, oesophagus, mouth and pharynx, and probably prostate cancer and breast cancer.

Ionizing radiation

Leukaemia

Obesity

Cancers of the breast, bowel, kidney, uterus and oesophagus.

Lack of physical activity

Bowel and breast cancer

Alcohol consumption

Cancers of the liver, breast, pharynx, larynx, oesophagus and bowel (beer).

Air pollution

Lung cancer
Alkylating agents Bladder
Polycyclic hydrocarbons Lung, skin
Aromatic amines (dyes) Bladder
Nickel Lung, nasal sinuses
Benzene Acute myelocytic leukaemia
Arsenic Lung, skin
Chromium Lung cancer
Oestrogens Uterus
Androgen hormones Prostate cancer
Helicobacter Pylori Stomach

Human Papilloma Virus

Cervix, head and neck

Start early

With this degree of uncertainty, it is important that cancer prevention strategies, such as reduced sun exposure, smoking cessation, and increased fruit and vegetable intake, are adopted as early in life as possible. It is likely that for many cancers the most vulnerable time for cancerous genetic change initiation is childhood. It is therefore equally important for children to avoid exposure to known cancer causing substances and adopt practices that will reduce their overall risk (e.g. consuming a diet high in fruit and vegetables).

Cancer rates will increase due to lifestyle factors being ignored

While smoking rates are declining in Australia, many other lifestyle causes of cancer are actually on the rise. In Australia, these include decreasing physical activity levels, increasing weight, decreasing fruit and vegetable consumption, excessive alcohol consumption and increasing exposure to air pollution. If these trends continue, it is thought that the incidence of some cancers could grow by up to 50 per cent in the next 20 years. A sobering thought!!

 

Source: Australian Institute of Health and Welfare: Australian Burden of Disease Study 2011

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Cancer and diet

Environmental factors, a large percentage of which are dietary related, account for about 50 per cent of all cancers. Dietary modification can play an important part in cancer prevention, with a reduction in cancer deaths of up to 30 per cent being achievable. Well over half of this benefit originates from the consumption of at least five servings of vegetables and two servings of fruit per day. With this in mind, it is most unfortunate that the amount of fruit and vegetables eaten by Australians continues to decline and at present only about eight per cent of Australians eat the recommended amount of fruit and vegetables.

Dietary recommendations to prevent cancer from the World Cancer Research Fund

In 2018 the World Cancer Research Fund published its second major review of scientific studies relating to diet and cancer prevention. (www.dietandcancerreport.org). This review assessed all the reliable evidence available on this subject; a mammoth task involving assessing many tens of thousands of studies. It is undoubtedly the most comprehensive source of information about this important topic.

It is the report's opinion that about one third of all cancers can be prevented by appropriate food consumption and nutrition combined with adequate physical activity and avoidance of obesity (and perhaps as many again would be prevented by stopping smoking). The main findings of the report are included in the boxed section below.

The 2017 World Cancer Research Fund report - Eight general and two special recommendations regarding diet and reducing cancer

The report's findings resulted in the following set of eight general and two special recommendations regarding diet and reducing cancer being made. (The actual recommendations appear in bold type. Additional information provided is either adapted from the report or from the author of the web site.)

1. Be healthy weight

  • This includes children, adolescents and adults. It is important to avoid weight gain and increases in waist circumference in adult life.
  • An adult body mass index of 21 to 23 is ideal for adults

2. Be physically active as part of everyday life - Walk more, sit less

  • Aim for 60 minutes of moderate activity, such as brisk walking, every day or 30 minutes of 30 minutes of more vigorous physical activity per day. (Adults presently doing little physical activity will need to increase activity levels gradually.) Sedentary activities such as watching television should be limited.
  • Limit sedentary habits
  • (Being physically active is beneficial irrespective of the effect it has on the person's weight.)

3. Limit intake of 'fast foods', sugar sweetened drinks and other processed foods high in fat, starches and sugars

  • These foods promote weight gain due to their high energy content. Energy dense foods are classified as those with more than 225 to 275kcal per 100g of food. Such foods include many foods in the following groups:
    • Drinks with added sugar (e.g. soft drinks) and excessive amounts of fruit juices
    • Most takeaway foods
    • Many processed foods
    • Confectionery
    • 'Sweets' / treats type foods such as icecream, doughnuts, cakes / biscuits etc

4. Eat a diet rich in wholegrains, vegetables, fruit and beans

  • Eat a diet high in all types of plant foods - Eat least five servings of a good variety of fruit and vegetables per day. (Presently Australian authorities recommend seven servings.) A serving of vegetables weighs 60 to 90 g (equivalent to about half a cup) and a portion of fruit weighs about 150g (for example one apple or two apricots). Raw vegetables, salads, green vegetables, tomatoes, onion family, carrots and citrus fruits are especially good, but a good variety of all fruits and vegetables is vital. Fruit and vegetable juices are good options, as are dried fruits.
  • Eat relatively unprocessed cereals (grains) and/or pulses (legumes) with every meal.
  • Consume at least 30g of fibre per day
  • Limit refined starchy foods

5. Limit intake of red meat and processed meat

  • If eating red meat, consume less than 350g to 500g of cooked red meat per week (An appropriate serving size is about 80g, which is a piece of meat about the size of a pack of playing cards).
  • Alternatives to red meat include a variety of fish, poultry and red meat. All meats should be lean and have visible fat removed (or the skin removed in the case of poultry).
  • Processed meat includes meats that are smoked cured or salted. (Such meats can be eaten occasionally but ideally should not form a regular part of the diet.) They increase the risk of stomack cancer.

6. Limit alcoholic drinks - For cancer prevention it is best not to drink alcohol

  • Alcohol intake should be limited to no more than 20g (2 standard drinks) per day for men and 10g (one standard drink) for women. (To avoid the likelihood of addiction, all people should have two 'alcohol free' days per week.)
  • Children and pregnant women should consume no alcohol.

7. Do not use supplements for cancer prevention - Aim to meet nutritional needs through diet alone

  • Dietary supplements are not recommended for cancer protection. It is important to remember that most of the evidence relating the benefit of foods in preventing cancer was gained by looking at taking foods, not dietary supplements. The fact that a particular food helps reduce cancer does not imply that a supplement containing one or two of its constituent compounds will give the same benefit.

Special recommendation 1 - Mothers to breastfeed; babies to be breastfed.

  • Aim to breastfeed infants exclusively up to six months and continue with complementary feeds thereafter

Special recommendation 2 - All cancer survivors to receive nutritional care from an appropriately trained professional.

  • If able to do so, and unless otherwise advised, cancer survivors should aim to follow the recommendations for diet, healthy weight, and physical activity.

One point worth noting is that, despite a daily multitude of reports in the media blaming all sorts of foods for all sorts of cancers, this extremely thorough review found good evidence to support only a few specific associations between foods and cancers. Studying food / nutrition and cancer is extremely difficult and this is one reason why this may have been the case. Just as one swallow does not make a summer, one study usually does not prove a cancerous link between a food and a cancer. Studies vary greatly in their size and quality and it is best to wait for changes in official recommendations by well-recognised organisations such as the Australian Cancer Council before thinking of making dietary changes. (Such changes are not common because these organisiations need to be as sure as possible that the advice they give is correct. Unlike the media, they are not there to entertain.)

More information about this topic, including a table summarising the above study's findings regarding the effects of individual foods / nutrients in causing / preventing specific types of cancers, can be found in the separate section on diet and cancer. (Diet and cancer prevention.) They are worth reading.

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Hints for preserving protective nutrients in vegetables and fruit

  • Start with fresh vegetables and herbs whenever possible. Canning (and to a lesser extent freezing) fruit and vegetables destroys a proportion of their vitamin content, although the same occurs when fruit and vegetables are stored for long periods. Prolonged storage is common practice in the fruit and vegetable industry, with times from picking to supply usually being from several weeks up to months (e.g. apples, kiwifruit, pears, grapes and oranges) The best place to get fresh produce is at local farmers’ markets, although there is less choice. (See www.farmersmarkets.org.au for information regarding local market locations.) A home vegetable garden is a great option and is an wonderful activity for any children in the household!!
  • Try to eat fruit when in season. Fruit purchased out of season is likely to have been stored for long periods. (Bear in mind that overseas sourced fruit will have a different season to local produce.)
  • Eat fruit and vegetables with the skins left on where possible. (This includes potatoes, the skin of which contains an anti-carcinogen.)
  • Do not store fresh foods for long periods; a week at most.
  • Store fruit and vegetables in a cool, dark place.
  • Keep pieces as large as possible when chopping/slicing prior to cooking.
  • When cooking vegetables, minimise both cooking time and cooking water to reduce vitamin losses. The preferred cooking method should be steaming, followed by micro-waving (in only a very small amount of water), stir-frying and lastly, boiling. If boiling, add food only when the water is boiling and boil in the smallest amount of water possible.
  • Do not soak vegetables before cooking.
  • Do not use copper pots or utensils as they can increase losses of some vitamins, particularly vitamin C.
  • Use cooking water and liquid from canned foods in sauces, gravies etc.
  • Do not use baking powder to preserve vegetable colour during cooking as it increases vitamin losses.

Water soluble vitamins are the ones that are destroyed by cooking andthey also dissolve into water. Maximum losses during cooking vary from 10 per cent for vitamin B12 to 100 per cent for more unstable vitamins, such as folate and vitamin C. Fat soluble vitamins are more hardy and don’t dissolve in cooking water.

Heating is not always bad. While heating tomatoes decreases its vitamin C content, it increases the availability of antioxidants including lycopene.

Cancer and physical activity

Physical inactivity is responsible for increasing the incidence of several types of cancer, the most important ones being bowel and breast cancer. This is discussed more fully in the section on physical activity.

Medical Xrays and cancer

Generally speaking a simple Xray such as a chest Xray gives quite a small dose of radiation that is of little concern with respect to increasing cancer risk. (See chart below.) However, some Xrays, such as CAT scans and whole body scanning, deliver a much larger dose and if they need to be repeated can start to present a potential problem. Such Xrays are, of course, rarely done without good reason. (The exception to this generalisation is CT scans used for cancer screening purposes. This practice has not been shown to be beneficial and is not recommended. )

MRI Scans: MRI scans do not use ionising radiation and thus do not increase the risk of cancer. (They do, however, take longer and are more expensive.)

Increased cancer risk from X-ray radiation exposure

 

Typical dose

(mSv)

Equivalent period of natural background radiation

Lifetime additional risk of cancer if procedure done on a 36 year old man

X-Ray examination

 

 

 

Limbs / joints

<0.01

<1.5 days

0.000%

Teethe (single bite wing)

<0.01

<1.5 days

0.000%

Chest (single AP)

0.02

2 days

0.001%

Skull

0.07

11 days

0.001%

Cervical spine

0.08

2 weeks

0.001%

Thoracic spine

0.08

2 weeks

0.001%

Abdomen

0.7

4 months

0.005%

Pelvis

0.7

4 months

0.005%

Lumbar spine

1.3

7 months

0.011%

Barium enema

7.0

3.2 years

0.059%

CT head

2.0

1 year

0.015%

CT chest

8.0

3.6 years

0.052%

CT abdomen/ pelvis

10.0

4.5 years

0.104%

Nuclear medicine studies

 

 

 

Lung perfusion (Tc-99m)

1.0

6 months

0.016%

Thyroid scan (Tc-99m)

1.0

6 months

0.036%

Bone scan (Tc-99m)

4.0

2 years

0.047%

Cardiac stress test (Technetium)

6.0

2.7 years

0.070%

Reference: www.xrayrisk.com

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2. Medical intervention to help find and treat cancers before they become incurable

Medical intervention prevents deaths from many cancers with its effectiveness varying with each type of cancer. Interventions can take various forms as follows.

More effective screening and other programs to help recognise cancers early will hopefully reduce cancer death rates by at least 25 per cent in the following 25 years. To maximize the benefits from screening and early detection, people need to be aware of screening programs relevant to them and know the early signs of various types of cancer. Early detection is effective in reducing deaths from many cancers including colorectal, bladder and kidney cancers, and especially melanoma.

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A. Screening - Diagnosing cancer before its symptoms have occurred

What is screening?

Screening for cancers involves performing an investigation that might indicate the presence of a cancer. It is performed on a selected group of individuals that may or may not be at increased risk of developing the disease being looked for.

It is very important to understand that screening tests are not the appropriate method for investigating people with existing symptoms. People with symptoms need to have these assessed and investigated by their doctor as soon as they are found.

Most screening tests do not provide a diagnosis. Rather, they indicate people at increased risk of the condition being screened for. Further investigations are usually necessary to make a definite diagnosis. (There are exceptions to this general rule, an example being using colonoscopy to screen people at higher than average risk of bowel cancer.)

Why do we need to be screened for some cancers?

Most people (85%) who die from cancer die from the spread of the cancer to other parts of the body (metastatic disease). For most cancers, the pathway from cancer initiation to local invasion (local spread) to metastatic disease takes a long time. For example, the initiation of malignant melanoma often occurs by the age of 15 years but most Australians are over 40 when the disease is diagnosed. In the case of bowel cancer, the progression from a non-cancerous polyp lesion to invasive cancer is thought to usually require at least ten years.

This time lag between cancer initiation and spread allows diagnosis of the cancer before it has had time to spread and this ‘early diagnosis’ can allow a cure in many cases.

Deciding whether a particular screening program will be of benefit to you?

It is important to understand that screening involves doing medical procedures on WELL people that are intrusive, cost money and involve side effects. It is therefore critical that a substantial overall benefit exists for those being screened before a screening program is implemented. The following quote emphasizes what this implies for doctors recommending a screening procedure. 

“For decades, Australia has accepted the World Health Organization guidelines for evaluating the worth of screening. These guidelines, recently updated, state “. . . in screening there is an ethical responsibility to conduct programs that will be of overall benefit to those who are screened and will minimize harm and anxiety that will arise. It is not simply the offering of medical tests for people to accept or reject as they wish. This responsibility implies that if evidence is not available from valid studies on the effectiveness of screening, screening should not be offered.”

Strong K, Wald N, Miller A, Alwan A, on behalf of the WHO Consultation Group. Current concepts in screening for noncommunicable disease: World Health Organization Consultation Group report on methodology of noncommunicable disease screening. Journal of Medical Screening 2005; 12; pp12 - 19

For general screening programs that target a community to be of benefit to that community, then the majority of the community needs to participate. While most of these people will not benefit at all from screening, those that do may well have their life saved.

Factors affecting an individual's benefit from screening. Deciding on whether an individual will benefit from being screened for a particular cancer is a matter of balancing the following factors.

Most women (and a considerable number of men) who choose to have cancer screening will have an abnormal screening test result at some time in their lives

Screening programs commonly involve having tests at regular intervals over an extended period of time and each time there will be, as well as true positive results, a number of false positive results. In women who choose to participate fully in the recommended screening programs for breast, cervical and colon cancer;

  • 50 per cent will at some time have a mammography abnormality that requires further investigation
  • 40 per cent will at some time have a Pap smear abnormality that requires further investigation
  • 50 percent will have a positive faecal occult blood test that is likely to require investigation by colonoscopy.

Obviously most of these abnormalities will be false positives but they will all cause stress and worry while they are being investigated. (And some people will continue to worry after being cleared of disease.)

Aids at deciding on the benefits of screening

Decision aids: From the above it can be seen that deciding whether to have a screening test or not can be reasonably complicated. Luckily, some ‘decision aids’ have been designed to help people make this choice and many more are being presently designed. (See ‘Further information’ at the end of this section. The Ottawa Health Research Institute and Sydney Health Decision Group web sites are a good place to start.)

Government recommended screening: Government health authorities in Australia are very aware of all these issues. In addition, they have to consider the high financial cost of screening programs. (The cost of screening varies depending on whether or not each screening test is associated with a GP visit, but a very rough guide is about $25,000 per year of life saved.) Thus they are only likely to recommend screening where there is a clear overall benefit to the population who participate and their approval for a screening program should help people make this decision (and visa versa).

Even so, the benefit gained is an overall community one and there is no guarantee that any particular individual will benefit. So it is a personal choice.

U.S. Preventive Services Task Force (USPSTF) cancer screening ratings

In the USA, the U.S. Preventive Services Task Force (USPSTF) rates its recommendations regarding screening as follows.

A rating: The USPSTF strongly recommends that clinicians provide [the service] to eligible patients. The USPSTF found good evidence that [the service] improves important health outcomes and concludes that benefits substantially outweigh harms.
B rating: The USPSTF recommends that clinicians provide [this service] to eligible patients. The USPSTF found at least fair evidence that [the service] improves important health outcomes and concludes that benefits outweigh harms.
D rating: The USPSTF recommends against the service. There is moderate or high certainty that the service has no net benefit or that the harms outweigh the benefits.
I rating: The USPSTF concludes that the evidence is insufficient to recommend for or against routinely providing [the service]. Evidence that the [service] is effective is lacking, of poor quality, or conflicting and the balance of benefits and harms cannot be determined.

Ratings for common cancers (and the year they were made) are as follows:

  • Bowel cancer screening using FOBT (faecal occult blood testing) for adults under 75 yrs old – ‘A’ rating (2008) Click here
  • Cervical cancer screening using Pap smears -  ‘A’ rating (2003) Click here
  • Breast cancer screening - ‘B’ rating (2009) Click here
  • Prostate cancer screening using the PSA test -  ‘D’ rating (2012) (Previously it had an ‘I’ rating.) Click here

Source: US Preventive Services Taskforce:  Link

 

Australian Government recommended screening program for people with a normal risk of contracting the disease

(People with an elevated risk of a particular cancer will need to discuss earlier / additional screening with their doctor.)

Cancer type

Screening procedure

Frequency

Females

Cervical cancer

Pap smear

Every 2 years from age 20 or two years after first sexual intercourse. Usually ceases at age 70 in women with no history of cervical abnormalities during testing.

Breast cancer

Mammogram

Every second year from age 50 to age 70

Bowel cancer

FOBT (Testing for blood in bowel motions)

Every two years from age 50 to age 70

Males

Bowel cancer

FOBT (Testing for blood in bowel motions)

Every two years from age 50 to age 70

Prostate cancer

There is insufficient evidence for government health authorities to make a decision regarding recommending routine screening for prostate cancer.

Screening examinations at GP check ups

Several examinations should be done at adult routine GP check ups to help identify cancer early. These include:

Different levels of screening

In some diseases, there are different ‘levels’ of screening available for people with different risk levels for the disease. For example, testing the faeces for blood is an easy non-invasive screening test for bowel cancer that is suitable for everyone over the age of 50. Colonoscopy is a more invasive, risky, and expensive procedure that is usually only recommended as a screening test for people who have a higher risk of bowel cancer.

Screening will not detect all cancers

People who are screened for a particular cancer and have a negative result cannot assume that they therefore will not get that cancer for two reasons.

Thus, if a person develops symptoms that might be due to cancer, it is important that these symptoms are brought to a doctor’s attention and investigated quickly irrespective of whether the person has had a recent negative screening test. (Symptoms of common cancers are listed later in this section.)

Full body CT scanning as a screening test

Full body CT scans have recently been promoted as a means of screening healthy people for early cancers. There is no evidence that such scans are helpful in increasing life expectancy and they may well be giving false reassurance as early cancers may be missed. They may also discover abnormalities that will never give any problem and thus cause unnecessary worry. The dose of radiation involved is also excessive and may cause long-term harm if such scanning is done regularly. They are not recommended.

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B. The importance of early recognition of cancer symptoms

Many people delay reporting symptoms they suspect may be due to cancer because they feel that nothing can be done; they feel it is the end of the road. Nothing could be further from the truth for several reasons.

Firstly, it is quite likely that the symptom will not actually be due to a cancer. Secondly, if a cancer is uncovered, proper treatment can allow a complete cure if the cancer is found early enough. It is important to realise that many common cancers have death rates less than half their incidence rates, indicating that over 50 per cent have been cured once found. And generally the earlier a cancer is found the greater the chance of a cure.

And even if a cancer is uncovered too late to permit a permanent cure, early diagnosis still allows optimum early treatment and this usually reduces the disability suffered and can also often increase life expectancy. Sixty per cent of all Australians with serious cancer will survive at least five years. This is a much better the life expectancy than that expected for a person with significant heart failure.

Thus, it is essential to report any possible cancer symptoms as early as possible.

Symptoms of common cancers

Cancer

Symptoms

Cancer in general
  • Weight loss
  • General fatigue

Lung cancer
  • Persistent cough
  • Wheeze
  • Coughing up blood
  • Shortness of breath
  • Chest pain
  • A chest infection that is slow to heal.

Present and past smokers need to be very vigilant regarding the onset of any of the above symptoms or of any changes in their usual symptoms, such as increasing cough, wheeze or shortness of breath.

Bowel cancer
  • Blood in bowel motions
  • Diarrhea or constipation
  • Mucous in bowel motions
  • Abdominal pain
  • A lump around the back passage

Breast cancer
  • Breast lump lumpiness or thickening in breast tissue (remember that breast tissue goes almost to the arm pit)
  • Change in breast shape
  • Nipple changes (inverting, dimpling, ulceration, crusting, unusual redness)
  • Discharge (especially if on one side or from one duct)
  • Bleeding from the nipple
  • Pain in the breast, especially if in one breast or when it does not improve after period.

Melanoma
  • A new pigmented lesion or any change in an existing lesion. (Melanomas are usually dark in colour but can be blue, red or even white)

Kidney cancer
  • Blood in the urine
  • Pain in the loin or abdomen
  • A swelling in the loin

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Some cancers do not need to be treated

Some cancers that occur relatively late in life and / or progress very slowly never get the chance to become a significant problem as the person dies of another disease beforehand. Many men with prostate cancer die without ever knowing they have the disease. With the increasing trend towards screening for caners, it is important that doctors are very careful in choosing the cancers they screen for and how they screen for them as it is quite likely that the same situation exists with other types of cancer. Being made aware of cancers that are not going to cause harm just causes unnecessary worry and creates unnecessary expense for the community. And there is no shortage of beneficial ways to spend any additional health funding that becomes available.

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A modern approach to cancer – We may have to 'learn to live with it'.

At the beginning of this chapter it was stated that a cancer occurs when there is a malfunction in the genetic control of the processes that determine a cell’s lifespan and ability to reproduce, allowing these processes to occur at a faster rate than would normally be the case. This change usually occurs in a single cell and is often caused by more than one factor. 
However, for two reasons, not all these changes lead to cancers that cause death.

(i) The body detects and destroys many early cancers - Gene abnormalities that can result in cancer probably occur quite often in the body. However, in most cases the development of a cancer is prevented by the body recognizing the abnormality in the cell and destroying the cell. This destruction of the abnormal cell can be done by the cell itself, an auto-destruction process, or by the body’s immune system (i.e. its general defence system). Unfortunately, sometimes this multi-pronged defence system fails and a cancer occurs.

(iii) All cancers are different - Each person’s body cells are unique and thus every cancer that occurs is also unique. This means that cancers originating from the same part of the body (e.g. the bowel) in different people may act very differently and this is part of the reason why some cancers are very aggressive and others are quite benign, never causing any problem.

Also, It is quite likely that a cell might be able to become cancerous via several different combinations of gene changes and these different types of cancer cells may act quite differently.

Finding cancers

In the past, cancers were diagnosed mostly because people presented with symptoms of the disease. This meant that the cancers that doctors saw and pathologists examined under the microscope were usually relatively advanced. Many people have suffered and died from these advanced cancers and our fear of cancer is based on the often poor outcomes of these cancer patients.

The advent of screening and more interest in researching the causes of cancers have meant that doctors and researchers are now seeing cancers far earlier in their ‘life cycle’, including in pre-cancerous stages. And the increasing use of screening techniques, such as mammography and faecal occult blood testing for detecting early bowel cancer, is going to mean that even more of these pre-cancerous lesions will be found in the future.

Research on such lesions has shown that the early cell changes that have previously been thought to inevitably lead to the cell becoming fully cancerous are quite common. For example, such changes are thought to exist in some cells:

However, the incidence rates of cancer in the community are much lower than these numbers, which means that many of these 'pre-cancerous' lesions are not developing into clinically significant cancers. They in fact remain insignificant because they:

It would perhaps be better if these lesions were not termed pre-cancerous, but the problem here is that some of them will develop into cancers; and unfortunately telling which ones will turn into cancers is not easy.

Unfortunately, the better doctors become at finding these early lesions, the more likely they are to find ones that never would have caused harm. In other words, screening inevitably involves over-diagnosis and thus over-treatment.

Doctors are fairly good at the process of identifying which lesions are going to cause future problems with cervical cancer because Pap smear screening has been going on for a long time and this has allowed the accumulation of considerable knowledge regarding the development of cervical cancer from early lesions.

In most other cancers there is much less information available and doctors are thus not good at predicting which early lesions are going to cause problems. This is less of a dilemma when the cancers are usually by nature less aggressive and occur later in life, such as many cases of prostate cancer. Some elderly men with prostate cancer, having examined the evidence, decide to have no treatment, preferring to adopt a wait-and-see approach.

In cancers that can be more aggressive and / or occur relatively early in life, such as breast cancer, all early lesions should be treated as doctors still just don’t know which will ultimately lead to cancer (and cause death if left untreated).

At present many people actually live unknowingly (and thus quite happily) with precancerous lesions that they never find out about. For example, there is no eaasy way to look for pre-cancerous thyroid lesions so doctors don't look for them and sjust ee what happens. (Most are relatively benign.) On the other hand we are less happy with adopting a wait and see approach to benign looking prostate cancer lesions that doctors think will not cause much trouble. Many men in this situation will still opt for treatment.

This type of scenario is likely to become more common as future researtch identifies other cancers that can, in some circumstances, be watched. This will not be an easy task unless we change our perception about early cancer. (Interestingly, most adults have no problems living with blocked heart arteries that will lead to heart attack; and many do nothing about reducing their risk factors for heart disease.)

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Further information

NSW Cancer Council (For information about any cancer topic)
http://www.cancercouncil.com.au/sem-ways-to-donate/?gclid=CPP12-e1_80CFQFvvAodW7gD6Q

Harvard University cancer risk assessment
http://www.diseaseriskindex.harvard.edu/update/
An interesting web site that allows people, by answering a variety of questionnaires, to calculate their personal risk of developing different types of cancer, including breast colorectal and prostate cancers. It also helps identify factors that can modify / reduce a person’s overall chance of contracting the particular cancer being looking at.

US Preventive Services Taskforce (ratings on the benefits and harms of screening for common cancers)
http://www.ahrq.gov/clinic/cps3dix.htm#cancer

Sydney Health Decision Group at the School of Public Health, University of Sydney
http://sydney.edu.au/medicine/public-health/shdg/

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

Australian Screening Mammography Decision Aid Trial
http://www.mammogram.med.usyd.edu.au

Informed health online (Cochrane Consumer Collaboration)
http://consumers.cochrane.org

The Cancer Council Australia
http://www.cancer.org.au/

UK National Screening Committee
https://www.gov.uk/guidance/nhs-population-screening-explained

US National Cancer Institute
http://www.nci.nih.gov/

 

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