The New York Times, as previously mentioned, is reporting a shift in screening policy at the the American Cancer Society, which is now saying that the benefits of early detection of many cancers, especially breast and prostate, have been “overstated”.
“We don’t want people to panic,” Dr Otis Brawley, the Society’s chief medical officer told the NYT. “But I’m admitting that American medicine has overpromised when it comes to screening. The advantages to screening have been exaggerated.”
The LA Times has another slant on the story.
Professor Ian Olver, CEO of Cancer Council Australia, says it is important to consider the pros and cons of screening for each type of cancer, rather than making blanket statements.
“It is not helpful to bundle prostate and breast cancer together in a discussion about the benefits of screening. The aim of screening is to diagnose cancer or pre-cancerous conditions early to significantly improve treatment outcomes. It should never be interpreted as guaranteeing cure for all individuals.
The term “over-diagnosis” can apply to people who have cancers detected by screening but who would have died of something else before the cancer would have been detected in the absence of screening. Obviously very slow-growing cancers would make over-diagnosis more likely.
After many years of mammographic screening for breast cancer, the International Agency for Research in Cancer has estimated that the reduction in the death rate from breast cancer in the main target group of 50 to 69 year olds is 35%, a significant mortality benefit, but not without some cost.
The estimate from the initial mammography trials of over-diagnosis is 2 to 3% (that is cancers that would not have progressed if left untreated). Adding in the pre-invasive DCIS (ductal carcinoma in situ) the range of estimates of over-diagnosis is around 9%. However, this still means that the vast majority of detected cancers did need treatment and that lives were saved.
Prostate cancer is quite different. There is no history of population screening programs to study. Two large randomised trials of PSA testing of asymptomatic men from last year had differing results.
No change in the death rate from prostate cancer was found in an American study while in the European study a 20% relative decrease in mortality was reported.
The overtreatment rate in this study was that for every 49 men who underwent prostatectomy only one life was saved, yet each was at risk of the side effects of impotence and incontinence.
Over-diagnosis and over-treatment are why Cancer Council Australia and a number of other health groups recommend PSA screening be an individual choice. Further research should be encouraged in this and other cancers to find better screening tests and tests that will identify indolent cancers which don’t need immediate treatment.
So, although it has always been known that not every individual will benefit from screening, in the proven population screening programs, for cervical cancer, breast cancer and colorectal cancer, the likelihood of reducing deaths from these diseases outweighs the chance of over-diagnosis.
Nonetheless individuals need to be informed of both the risks and benefits.
It would be a pity if doubts about over-diagnosis discouraged participation in these programs by the groups most likely to benefit or dissuaded government from completing the roll-out of the colorectal screening program, so that it could not reach its full potential of saving 30 Australian lives each week.”