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Professor Paul Glasziou. Photo: Bond University

Researchers issue cancer overdiagnosis warning

Australian researchers have renewed concerns that people are increasingly being diagnosed with cancers that will do them no harm if left undetected or untreated, following new research into five cancer types.

Lead author Professor Paul Glasziou, from Bond University, looked at data from the Australian Institute of Health and Welfare to compare how the lifetime risk of five cancers had changed between 1982 and 2012.

In 2012, 24 per cent of cancers or carcinomas in men were overdiagnosed, including 42 per cent of prostate cancers, 42 per cent of renal cancers, 73 per cent of thyroid cancers and 58 per cent of melanomas.

For women, 18 per cent of cancers or carcinomas were overdiagnosed, including 22 per cent of breast cancers, 58 per cent of renal cancers, 73 per cent of thyroid cancers and 58 per cent of melanomas.

The researchers said this is exposing people to unnecessary surgeries and chemotherapy.

“Cancer treatments such as surgery, radiotherapy, endocrine and chemotherapy carry risks of physical harms,” the study's authors said.

“In the absence of overdiagnosis, these harms are generally considered acceptable. In the context of overdiagnosed cancers, however, affected individuals cannot benefit but can only be harmed by these treatments.”

Compared to 30 years prior, Australians in 2012 were more likely to experience a cancer diagnosis in their lifetime.

Glasziou said increasing rates of diagnosis were a result of improvements and wider use of testing and screening, but added the problem is some screening identifies abnormal cells that look like cancer but don’t behave like cancer.

However, he added addressing that problem is not easy, as some types of screening are important.

He said: “While much of the overdiagnosis is due to screening, many overdiagnosed cancer cases are incidental findings, that is, the patient is being tested for something else when the cancer is detected.

“Getting the balance right between too little and too much screening and testing will not be easy, but this is an important step.”

The authors said rates of avoidable overdiagnosis need to be reduced to the lowest level "compatible with targeted screening and appropriate investigation".

Co-author Associate Professor Katy Bell of the University of Sydney said the findings also suggest an important role for health services, such as the Australian Institute of Health and Welfare and state cancer registries, in detecting potential overdiagnosis and alerting health policy decision makers to the problem early on.

“Patterns of increased test use, cancer incidence or treatment rates without corresponding rises in mortality could indicate emerging areas of overdiagnosis,” she said.

“People still need to remain vigilant when it comes to early detection of cancers, however they need to be informed and engage in shared decision making with their medical professionals about the harms of cancer screening and other associated procedures.”

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