It seems that there isn't a month that goes by when I don't see an online petition calling for the introduction of, or an increase in, some type of cancer screening. It's an emotive topic that has touched many people's lives. It's also a really interesting subject, especially since it’s an area in which there seems to be a widening disconnect between public perception and evidence.
The logic in favour of screening is clear. Screen otherwise healthy people for various types of cancer and we can pick up any developing cases as early as possible. That means the cancers are easier to treat and we save more lives. It inherently feels like a great idea and like something we should all do more of. So why is it that there is a growing undercurrent of concern emerging among healthcare professionals?
Contrary to what the online petitions and newspapers will have us believe, this scepticism about screening has very little to do with cost. The concern is that cancer screening may actually be doing more harm than good.
The problem starts with the evidence. The number of deaths from the specific cancer we are screening for seems like a perfectly reasonable outcome to use in trials, but in reality it doesn't show the full picture. A fascinating paper in the BMJ found that the majority of randomised trials showed a decrease in specific cancer deaths, but either no difference – or even a higher – overall death rate. So, in other words, you might be less likely to die of that breast/ovarian/prostate cancer, but more likely to die of something else.
So what is going on here? How can a good thing such as screening actually increase death rate? There are two broad possibilities:
1. Even if the trials are large enough to detect a reliable difference in cancer-specific deaths, they might not be adequately powered to detect differences in overall death rates;
2. Something about the screening is causing harmful effects, which make people more likely to die.
There is currently too little information to distinguish which it is – indeed, the most probable answer is a mix of both. The problem with the former possibility is that even when trials are pooled, data can still show an increase in overall death rates. And the problem with the latter is that there is so very little information that it is hard to pinpoint exactly what the negative effects of screening may be.
False positives are an obvious problem, yet what about patients with a truly positive result but a non-harmful cancer? Unnecessary treatment, the stress of a cancer diagnosis, an increase in anxiety, a more laissez-faire attitude to lifestyle – and even an increase in suicide rate – are all possible contributory factors.
As more evidence emerges, it seems more and more likely that the downsides of screening might well outweigh the benefits, however counter-intuitive that seems. That leaves us healthcare professionals with a difficult but extremely important role: cutting through the emotive language and long-held misconceptions that cling to cancer screening to communicate what the evidence tells us.