Replies to post #198968 on Biotech Values

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Prasad V, Lenzer J, Newman DH. Why cancer screening has never been shown to “save lives”—and what we can do about it. BMJ 2015;352. http://www.bmj.com/content/352/bmj.h6080

Despite growing appreciation of the harms of cancer screening, advocates still claim that it “saves lives.” This assertion rests, however, on reductions in disease specific mortality rather than overall mortality.

Using disease specific mortality as a proxy for overall mortality deprives people of information about their chief concern: reducing their risk of dying. Although some people may have personal reasons for wanting to avoid a specific diagnosis, the burden falls on providers to provide clear information about both disease specific and overall mortality and to ensure that the overall goal of healthcare—to improve quantity and quality of life—is not undermined.

In this article we argue that overall mortality should be the benchmark against which screening is judged and discuss how to improve the evidence upon which screening rests.


Gigerenzer G. Full disclosure about cancer screening. BMJ 2015;352. http://www.bmj.com/content/352/bmj.h6967

Communication about cancer screening is dodgy: benefits are overstated and harms downplayed. Several techniques of persuasion are used. These include using the term “prevention” instead of “early detection,” thereby wrongly suggesting that screening reduces the odds of getting cancer. Reductions in relative, rather than absolute, risk are reported, which wrongly indicate that benefits are large.1 And reporting increases in 5 year survival rates wrongly implies that these correlate with falls in mortality.2 Prasad and colleagues put their finger on another misleading practice: claiming that screening “saves lives” despite the lack of proof that overall mortality is decreased.3

A fall in cancer specific mortality alone cannot prove that lives are saved—the cause of death may be systematically misclassified or screening and subsequent cancer treatment may increase deaths from other causes, most likely as a consequence of overdiagnosis and overtreatment.3 4 To prove that screening saves lives one needs to find a difference in overall mortality. Yet detecting such a difference, if it exists, with reasonable statistical power in the general population would require studies with millions of participants. Can we get around this dilemma?

Prasad and colleagues propose reporting overall mortality in addition to cancer specific mortality and, if there is no difference in overall mortality, to stop claiming that screening saves lives. I agree but would like to add some additional points to their call for more honesty.