...And Challenging the Campaigns

Cancer screening campaigns are everywhere. And despite disagreement within the medical community around effectiveness, the message most often delivered to patients is that screening allows them to catch cancer early, and increases their chance of survival. But does it?

With more studies emerging that are calling this into question, or can’t provide a definitive answer, more patients are thinking twice about certain types of screening (1). And now, an article published in the BMJ (2) has further challenged preconceptions and thrown down the gauntlet for researchers, arguing that the way cancer screening is evaluated needs to change.

The crux of the argument is this: judging screening programs on their ability to reduce death from cancer is simply not enough, and assessing disease-specific mortality rather than overall mortality, fails to provide the entire picture. How many patients die of treatment complications (possibly after being diagnosed with a slow-growing cancer that wouldn’t have caused death)? How many commit suicide? How many die of an expected downstream effect of screening? The studies being conducted now, argue the study authors, simply aren’t powerful enough to answer these questions. And if you analyze what existing studies are able to tell us, the numbers aren’t promising: a systematic review of cancer screening meta-analyses found that three out of 10 showed reductions in disease-specific mortality, but none showed overall mortality reductions (3). And ultimately, the authors state, overall quantity (and quality) of life is of most importance to patients.

“The big assumption in cancer screening research has been that lowering disease-specific mortality will translate into a survival benefit. But that’s never been shown explicitly,” says article co-author Vinay Prasad; “It is possible, and in some cases maybe even plausible, that avoiding death from one cancer may be offset by slight increases in treatment-related mortality, or mortality from off-target effects.”

And it’s not just the studies that need to improve, its patient education too. In one survey, 68 percent of women believed that breast screening would lower their risk of getting breast cancer, 62 percent thought it would at least halve the rate of breast cancer, and 75 percent believed that 10 years of regular screening would prevent 10 breast cancer deaths per 1,000 women (4). The real numbers are of course nowhere near as positive, with a 2013 Cochrane review concluding that, for every 2,000 women screened over 10 years, one woman will avoid dying of breast cancer, and 10 healthy women will undergo unnecessary treatment (5).

So what can be done to effect change? The BMJ article’s authors suggest larger trials with the capacity to assess overall mortality, starting with participants in only the highest risk groups for the cancer in question. Although this is likely to be expensive, Prasad argues that “the amount of money and investment that western civilization is spending on cancer screening currently is orders of magnitude more than the cost it would be to really test these screening tests in very robust studies, for the endpoints that really matter to patients.”

Prasad and his colleagues also recommend that patients should be given all the information they need to make well-informed decisions on screening; and they conclude with a call to action: “We call for higher standards of evidence, not to satisfy an esoteric standard, but to enable rational, shared decision making between doctors and patients.”