The risks of overdiagnosing illnesses such as breast cancer

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A series of papers in the medical journal BMJ looks at the risks and harms to patients due to overdiagnosis of illnesses such as breast cancer and aneurysm.

It’s all about medical tests throwing up positive results and subsequent treatment for illnesses which may have not needed intervention in the first place.

The papers discuss how the over-detection and overtreatment of illnesses which are not life threatening is becoming more common due to the presence of advanced diagnostic technologies.

In one article, part of a series in the journal’s Too Much Medicine campaign, a Sydney-based researcher says there’s conflicting information about overdiagnosis of breast cancer.

In 2012, an independent UK panel estimated about 19% of breast cancers diagnosed among women invited to mammogram screening were in fact overdiagnosed. But other estimates have been higher (up to 50%) or lower (less than 5%).

Achieving consensus seems unlikely in the short term, but resolution should be a high priority so that women can be given objective, balanced and uncontested information, writes Alexandra Barratt, Professor of Public Health at the University of Sydney.

Breast cancer is the most common cancer in women worldwide. Early trials reported that screening reduced the risk of dying from breast cancer by around 30% in women over 50 and led to publicly funded mammography screening programs in many countries in the 1980s and ’90s.

Although this has led to large increases in detection of early breast cancer, rates of advanced cancer have declined only slightly or remained relatively stable, suggesting that mammography screening is detecting low risk or non-progressing breast cancer which would never have become life threatening.

In the UK screening program, 99% of women with screen-detected breast cancer undergo surgery and around 70% also have radiotherapy and hormone therapy.

If around 20% of these breast cancers are overdiagnosed, then about 20% of these women are undergoing treatments to “cure” a disease which they would never had had without screening, says Barratt.

She also argues we should think twice before introducing new breast imaging technologies, such as tomosynthesis (3D mammography) or extending screening to older and younger women, until incremental net benefit to women has been demonstrated in high quality studies.

“Breast cancer research has led the way in developing awareness of the potential harms of overdiagnosis and overtreatment,” says Barratt. “Increasing awareness and understanding of overdiagnosis in relation to the early detection of lung and thyroid cancers, as well as breast and prostate cancers, is needed and should be prioritised in public communication initiatives.”

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