The next best thing to a crystal ball?
Medical screening is when you're tested for conditions and diseases before there are any signs or symptoms. Although there are a fair few issues with screening programs, they've proven to be effective public health initiatives in some cases.
In Australia, government-funded screening is available for breast cancer, bowel cancer and prostate cancer. We look at how effective screening is and who is eligible for free screening, and we also look at the pros and cons of genetic testing for cancer.
The government funds screening where it believes that the benefits outweigh the costs. The following criteria apply to screening in the public health system:
- The condition to be screened for should be an important health problem and it must be known to often be present in an early form without any symptoms.
- The test used should be simple, safe, and provide both few false negative and false positive results.
- Early treatment of the condition tested for must be proven to be effective.
These better outcomes must clearly outweigh any potential harm to people from the screening, such as false positives leading to unnecessary psychological stress, invasive diagnostic tests, and treatment with possible serious side effects.
The proposed screening program would not use resources that could save more lives and prevent more suffering if used in other ways. The health system should ensure that positive screening test results can be promptly followed up.
Bowel cancer screening
The National Bowel Cancer Screening program offers eligible Australians free bowel screening, using faecal occult blood tests (FOBT).Currently, Australians turning 50, 55, 60 or 65 years of age are invited to take part. From 2015 this will be extended to those turning 70 as well.
Further expansions are planned for 2017-18, when two-yearly screening will be phased in. When fully implemented, all Australians aged between 50 and 74 years will be offered free screening every two years.
If you don't want to wait for the program to catch up with you – especially if there's a family history of the disease – you can use a home test kit, such as the BowelScreen Australia test kit, which you can buy from participating pharmacies.
If you're over 50 years of age it is advised you take an FOBT every two years, even if you don't have any symptoms or a family history of bowel cancer. As with all screening tests, there will be false negative and false positive results. The FOBT is no exception, but it does meet international criteria for a screening test.
If your FOBT is positive it doesn't necessarily mean cancer – it could mean some other bowel condition. However, it does mean you need further investigation, usually in the form of a colonoscopy. Polyps that can go on to become cancerous or early cancers can be removed, which is why regular testing is important.
False negatives can also occur. Another test that may be used, either alone or in conjunction with FOBT, is sigmoidoscopy, which examines the lower part of the large bowel.
Breast cancer screening
The successful BreastScreen Australia program operates in more than 500 locations, using X-ray mammography. It provides free screening mammograms for women over the age of 40. The program targets women between 50 and 74 years of age, who receive invitations to be tested. Women aged between 40 and 49, and over 75 years of age, are still eligible for free tests, but don't receive invitations.
The program is one of the most comprehensive population-based screening programs in the world – with well over 1.6 million women screened in 2007-2008. The program has a goal of screening 70% of women in its target 50-74 year age group. It's currently only screening 54.9%; however, the target age group was increased by four years in the 2013-14 Federal Budget, which may explain some of the shortfall.
Breast compression during mammography is uncomfortable and it may discourage some women from getting a mammogram, but screening helps with early detection and a better chance of successful treatment. More than 4,280 invasive cancers were detected by the program in 2008.
How effective is breast cancer screening?
Regular two-yearly mammograms have been shown to pick up many small tumours in the early stages of development before they start to spread to other parts of the body. Most of these can be successfully treated.
BreastScreen Australia applies a rigorous accreditation process to all the services involved in the program. The accreditation standard applies nationally, and lasts for four years.
Since 1993, the mortality rates for women in the target age group of 50-69 years has steadily been in decline. In 1989, the mortality rate was 69 deaths per 100,000 women, and by 2007 it had decreased to 47 per 100,000.
Research is ongoing to find ways to improve the false negatives and false positives of screening tests. Technologies other than X-ray mammography, such as ultrasound and magnetic resonance imaging (MRI), are showing some promise, but so far only in conjunction with mammography.
Genetic screening can also be useful where there is a family history of breast cancer, but it can be expensive and raises quite difficult ethical issues, such as life insurance companies reducing their risk exposure and other family members not wanting to know their high-risk status. Cancer Australia has a useful guide to the genetic aspects of breast cancer.
Prostate cancer can be present in an early and treatable form without any symptoms, but if it's detected from symptoms later on, the chance of successful treatment is low. Prostate cancer is responsible for 30% of cancers in men and is the second most common cause of cancer deaths in males, after lung cancer.
Prostate cancer is a relatively slow-growing cancer. This means that elderly men who are diagnosed with prostate cancer are more likely to die from other causes. Those who develop prostate cancer at a younger age, including middle-aged men, are in more danger from the disease.
How effective is prostate cancer screening?
Prostate cancer often raises the levels of prostate specific antigen (PSA) in the blood, which is measured with a blood test. Other tests which can screen for prostate cancer include digital rectal examination (DRE) – checking the prostate by feel - which will pick up about half of all tumours over 1cm. Medicare will cover one PSA and one DRE test per year, and any subsequent tests to monitor suspected cancer.
However, some studies have shown that almost 76% of positive results from PSA tests have been false alarms, and that almost 18% of men will get at least one false-positive result after receiving 4 rounds of PSA tests. Also, about 15% of men with prostate cancer will not have a high PSA.
The false negatives and false positives contribute to the controversy around PSA testing. The Royal Australian College of General Practitioners guidelines recommend that GPs wait until they are specifically asked about screening before discussing the test with their patients.
The Prostate Cancer Foundation of Australia recommends that men over age 50, or over 40 if they have a family history of prostate cancer, should talk to their doctor about the PSA test and DRE once a year.
What about genetic testing?
"Bad" genes in our genetic makeup (our inherited DNA) may increase our chances of getting a certain disease. There are two ways to find out if you are at risk:
- looking at your family history for patterns of genetically determined (inherited) diseases
- having a genetic test for suspect genes linked to the specific disease.
We couldn't afford to test everyone to see if they might get one of the top 30 diseases, and many diseases with a genetic component are the result of several genes interacting, so finding the "main" gene doesn't always tell you a lot anyway. If genetic testing is suggested, it's usually being done to confirm or refute a strong suspicion of inherited disease from your family history and/or ethnic background. If your family history shows an increased risk of breast cancer, genetic testing might be offered.
Women who carry BRCA1 and BRCA2 gene mutations are at high risk of developing breast and ovarian cancer and a personalised "screening" program may include mammography and/or ultrasound, and even checking for ovarian cancer. Screening may begin at a much earlier age than for "average risk" women – usually five years before the age at diagnosis of the nearest relative.
Issues raised by genetic testing
Genetic testing can raise tricky issues, so counselling is advisable before going ahead. For example, if the test is positive, and there is no treatment (such as with Huntington's disease) will you feel worse than if you didn't know? Companies providing life or disability insurance may ask you for any genetic test results. If you don't know, you can answer questions honestly without losing policy benefits.
For more on genetic and other screening, see our article on direct-to-consumer health screening.