Screening – Does it Lead to Overdiagnosis?

Screening, in medicine, is a strategy used to identify an unrecognized disease in individuals often without signs or symptoms. This can include individuals with pre-symptomatic or unrecognized symptomatic disease. As such, screening tests are somewhat unique in that they are performed on persons apparently in good health. Screening interventions, we are told, are designed to identify disease early, thus enabling earlier intervention and management in the hope to reduce mortality and suffering from a disease.

Given below are some findings published in the British Medical Journal, an international peer reviewed medical journal, which has been published without interruption since 1840.

We are told that regular mammography screening is done to reduce mortality from breast cancer. It was argued that screening would either lead to less invasive surgery or simpler treatment. In reality it is found that it actually results in 30% more surgery, 20% more mastectomies, and more use of radiotherapy because of overdiagnosis ((Gøtzsche PC, et al. Breast screening: the facts-or maybe not: BMJ 2009;338:b86)).  Dr. Susan Bewley, Professor of complex obstetrics at King’s College London, states that for every 15 women who are given a diagnosis through screening and who will undergo treatment, only one life will be saved and three women will have been treated unnecessarily ((Kmietowicz, Zosia. New breast screening leaflet still denies women the full picture, says critic: BMJ 2013;347:f5735)).

Recent studies point to the fact that screening, typically for breast cancer, has often led to overdiagnosis. A 25 year study in Canada shows that annual mammography does not result in a reduction in breast cancer specific mortality for women aged 40-59 beyond that of physical examination alone or usual care in the community ((Miller AB, et. Al.Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial: BMJ 2014;348:g366)). As a matter of fact, a row has erupted in Switzerland after the Swiss Medical Board recommended that the country’s mammography screening programme for breast cancer be suspended because it leads to too many unnecessary interventions. In a report made public on 2 February 2014, the Board said that while systematic mammography screening for breast cancer saved 1-2 women’s lives for every 1000 screened, it led to unnecessary investigations and treatment for around 100 women in every 1000. “The desirable effect is offset by the undesirable effects,” said the report.((Arie S, Switzerland debates dismantling its breast cancer screening programme: BMJ 2014;348:g1625))

A report from another quarter also makes interesting reading. Many elderly men in the US are being screened inappropriately for prostate cancer, say researchers. The very old and those in poor health are unlikely to live long enough to enjoy any potential benefits from screening, whereas the harms are immediate and include anxiety, false positive tests ((Inappropriate prostate cancer screening is common among elderly US men: BMJ 2006;333:1112)). A national prostate cancer awareness programme in New Zealand has been criticised for glossing over the harms of prostate specific antigen (PSA) testing and of promoting population screening by the “back door.” The $US3.5million scheme is intended to provide men with access to evidence based, high quality information to help them decide whether they need their prostate checked. Posters and patient information booklets were sent to every general practice in the country last month. But the resources have prompted an angry reaction, including calls for doctors to boycott the programme outright ((Brill D. New Zealand prostate cancer awareness programme is likely to increase unnecessary PSA testing:  BMJ 2013;347:f7537)).

Does screening for depression improve outcomes in primary care? The UK National Screening Committee has determined that there is no evidence of benefit from depression screening to justify costs and potential harms and has recommended against it ((Thombs BD. Does depression screening improve depression outcomes in primary care?BMJ 2014;348:g1253)).

Here is another finding. Bowel cancer screening with fecal occult blood testing was thought to reduces the risk of dying from bowel cancer, however a new long term study has shown that bowel cancer screening does not influence all cause mortality, so patients won’t necessarily live longer ((Jacqui W. BMJ 2013;347:f5773)).

I leave it to the reader to draw the appropriate conclusions.

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