30,000 cancers overdiagnosed each year in an Australian study : a public health issue
Summary , Cécile Bour, MD
28 January 2020
Authors of australian study published in Medical Journal of Australia
Paul P Glasziou, Mark A Jones, Thanya Pathirana, Alexandra L Barratt and Katy JL Bell
Med J Aust || doi: 10.5694/mja2.50455
The obsession of our modern societies to track diseases through ever earlier detection is leading to a public health crisis, according to Australian authors who published in January 2020 their evaluation of over-diagnoses for five different cancers.
National data routinely collected by the Australian Institute of Health and Welfare (Australia's national agency for health and welfare information and statistics) were analyzed to estimate risks in population to have a cancer during lifetime by comparing the current period (2012 data) with the past (1982 data).
This allowed to measure changes in these risks over the last 30 years. An adjustment has been made to take into account the risk of death and changes in risk factors over time.
The five different studied cancers are: prostate, breast, renal, thyroid cancers, and melanoma.
The authors propose an estimate of the proportion of cancer diagnoses in Australia which are reasonably due to over-diagnosis.
For women, an estimated 22% of breast cancers (invasive cancers, 13%), 58% of renal cancers, 73% of thyroid cancers, and 54% of melanomas (invasive melanoma, 15%) were overdiagnosed.
For men an estimated 42% of prostate cancers, 42% of renal cancers, 73% of thyroid cancers, and 58% of melanomas (invasive melanomas, 22%) were overdiagnosed.
Despite the relative uncertainty conceded by the authors themselves about these estimates, this result would be equivalent to an overdiagnosis representing about 18% of women's cancer diagnoses and about 24% of men's cancer diagnoses in Australia in 2012, i.e. about 11,000 women's cancers and 18,000 men's cancers overdiagnosed in Australia each year.
Absolute rates of over-diagnosis were highest for breast cancer and prostate cancer due to their higher baseline prevalence (rate of new cases + rate of cases already present).
The population is certainly aging, but screening programs are the big providers of overdiagnoses.
Cancer can also be overdiagnosed outside screening programs; for example overdiagnosis of thyroid cancer is attributable to incidental detection during imaging investigations of unrelated problems or the overdiagnosis of abdominal scans carried out for other causes.
Overdiagnosis is important to know and control because of the adverse effects on iatrogeny (pathology induced by treatments) and the associated additional costs.
Harms include the psychosocial impact of unnecessary cancer diagnoses, such as the increased suicide risk for men after being diagnosed with prostate cancer.
Cancer treatments such as radiotherapy, endocrine therapy and chemotherapy can cause physical harm, but the risks are considered acceptable if diagnosis is appropriate. Contrary, when someone is unnecessarily diagnosed with a cancer which would not be harmful for its health or life (overdiagnosis definition), this person will suffer harm as a result of the treatment, instead of enjoying the benefit of having been detected.
In other countries
This study is the first study to estimate overall cancer overdiagnosis on a national level.
A recent British analysis found that the “incidence of 10 of the 20 most common cancers in the UK has increased by more than 50% in both sexes since the 1980s.” These cancers included breast, kidney, prostate, thyroid cancers and melanoma, but also non‐Hodgkin lymphoma, oral, cervical, liver, and uterine cancers.
The authors therefore estimated overdiagnosis only for cancers with the typical epidemiologic signature of overdiagnosis: breast, prostate, kidney, thyroid cancers and melanoma (for which lifetime mortality has changed little in absolute terms).
UK cancer statistics released in January 2019 show very high survival rates for people with early stage cancers of these types, providing further evidence of probable overdiagnosis: 5‐year survival of 99% for stage 1 breast cancer, 100% for stage 1 prostate cancer, 100% for stage 1 melanoma, 89% for stage 1 kidney cancer, and 88% for thyroid cancer of any stage.
Editor’s note: Survival, often emphasized by INCa to justify the screening for breast cancer, is not an indicator of screening effectiveness, but a good over-diagnosis marker.
Survival measures the length of life with a cancer, If the cancer is not meant to kill its carrier, as is the case for cancers detected predominantly by screening, which are at low stage, survival can indeed be important since these cancers detected would never have led to the death.
The more over-diagnosis emerges, the more cancers that could have been ignored, and the better the survival rates, automatically.
The only appropriate indicator of the effectiveness of screening is mortality, or more precisely total mortality.
Cancer overdiagnosis has important implications for health policy.
First, rates of avoidable overdiagnosis need to be reduced to the lowest level compatible with targeted screening and appropriate investigation, instead of mass screening.
Strategies to reduce overtreatment of low-stage, therefore low-risk prostate, breast and thyroid cancers should be addressed.
A second, and perhaps more important implication is that health services need to be alert to new areas of overdiagnosis and to detect them early.
Editor’s note: Australia has already initiated an over-diagnosis action plan : https:/cancer-rose.fr/2018/10/15/un-plan-daction-national-contre-le-surdiagnostic-en-australie/
Editor’s note: The Australian example should prompt us to look downwards, in particular to the pink October commercial campaigns that culpably promote and train crowds to practice mass screening, encouraging women to be screened even outside the screening age range.
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