Overdiagnosis in About 20percent of Common Cancers

 | Post date: 2020/02/15 | 
About 20percent of five common cancers are the result of "overdiagnosis," concludes a study from Australia that analyzed over 30 years of national healthcare data. The figures were 18percent for women and 24percent for men.
Overdiagnosis is defined as the diagnosis of cancer in people who would never have experienced symptoms or harm had the cancer remained undetected and untreated, the authors explain. It often results from population cancer screening programs conducted in healthy individuals. 
Although the concept of overdiagnosis, and estimates of it from population screening programs, have been reported before, this study offers a new perspective.
This is "the first time that the risk of overdiagnosis has been quantified across five cancers anywhere in the world," said first author Paul P. Glasziou, PhD, Bond University, Robina, Queensland, Australia, in a statement.
The authors looked at five of the seven cancers for which overdiagnosis has been documented: breast, thyroid, renal, and prostate cancers, and melanoma.
Paul P. Glasziou, PhD
The results suggest that, overall, 18percent of these five cancers in women were overdiagnosed in 2012, accounting for 22percent of breast cancer cases and as many as 73percent of thyroid cancers.
In men, 24percent of these five cancers were overdiagnosed, including 42percent of prostate cancers, 58percent of melanomas, and 73percent of thyroid cancers.
The study was published online December 19 in the Medical Journal of Australia.
The reasons for overdiagnosis differ by cancer type, the authors comment, with breast cancer overdiagnosis "largely attributable" to national screening, and that for prostate cancer and melanoma because of "opportunistic but extensive" screening.
Overdiagnosed renal cancers, they add, tend to be found during abdominal imaging, and these incidentalomas also account for a proportion of overdiagnosed thyroid cancers, alongside the "excessive investigation of thyroid function tests."
Glasziou commented in his statement that, when it comes to screening, "the problem is that some screening identifies abnormal cells that look like cancer but don't behave like cancer."
"However, reducing that problem is not easy, as some types of screening are important."
"Getting the balance right between too little and too much screening and testing will not be easy, but this is an important step," he said.
Elaborating to Medscape Medical News, he said that some screening, such as for neuroblastoma and chest X-rays for lung cancer, does not work, and "the screening that does often has modest benefits and must be weighed against the several harms."
He believes that, to reduce overdiagnosis, there will need to be changes in the naming and classification of cancers, as well as changes to clinical practice and, "in particular," changes to "recommendations about screening and how to screen."
These ideas have been aired over the last few years by other groups, including a proposal to take the word "cancer" out of some diagnoses, and proposals to limit screening to individuals who are at higher risk of cancer instead of screening whole populations.   
Study Details
For this study, researchers looked at data on cancer-specific diagnosis, cancer-specific and all-cause deaths, as well as population numbers, collated by the Australian Institute of Health and Welfare for men and women between 1982 and 2012.
The team then calculated and compared current and past lifetime risks for cancer, adjusting for changes in the prevalence of risk factors over the course of the study period, such as cumulative sun exposure or body mass index.
The results show that, in women, the lifetime risk of being diagnosed with breast cancer increased by 3.4percent between 1982 and 2012, while the increase was 0.6percent for renal cancer, 1.0percent for thyroid cancer, and 5.1percent for melanoma.
Researchers estimated that, in 2012, 22percent of breast cancers (including 13percent of invasive cases), 58percent of renal cancers, 73percent of thyroid cancers, and 54percent of melanomas (including 15percent of invasive cases) were overdiagnosed.
This equated to 18percent of all diagnoses of these five cancers in women (8percent of invasive cancers).
Invasive cancer risk increased by 8.6percent in women during the study period, of which overdiagnosis of invasive breast, renal, and thyroid cancer, and melanoma explained 47percent of the increase.
In men, the lifetime risk of being diagnosed with prostate cancer increased by 8.2percent between 1982 and 2012, while the increase was 0.8percent for renal cancer, 0.4percent for thyroid cancer, and 8.0percent for melanoma.
It was estimated that 42percent of prostate cancers, 42percent of renal cancers, 73percent of thyroid cancers, and 58percent of melanomas were overdiagnosed.
This equated to 24percent of all diagnoses for these five cancers in men (16percent of invasive cancers).
The risk of invasive cancer increased by 10.9percent during the study period in men, with overdiagnosis of invasive prostate, renal, and thyroid cancers, and melanoma explaining 97percent of the increase.
Public Education Campaigns
In their discussion of the results, the team points to recent cancer statistics from the UK showing 5-year survival rates for stage 1 breast cancer of 99percent, 100percent for stage 1 prostate cancer, 100percent for stage 1 melanoma, 89percent for stage 1 kidney cancer, and 88percent for thyroid cancer of any stage.
These "very high survival rates," the team writes, provide "further evidence of probable overdiagnosis."
However, there has been a drive in recent years in the UK to diagnose patients with cancer at earlier stages to offer a better prognosis, which has been reflected by recent data suggesting few are now diagnosed at stage 4.
Glasziou agreed that this suggests a careful balance needs to be struck between public health campaigns urging early diagnosis and limiting overdiagnosis, but he emphasized that "earlier is not always better."
He highlighted the considerable harms that can be experienced by overdiagnosed patients undergoing cancer treatments.
Public education is needed, suggests coauthor Katy J. L. Bell, MD, Sydney School of Public Health, University of Sydney, New South Wales, Australia. "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," she said in a statement.
MedscapeCME & Education

Keywords: Oncology | Cancer | MedscapeCME | Education | Education | MedscapeCME | Cancer | Oncology |

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