Fair comparisons of treatments should measure important outcomes and avoid dependence on surrogate outcome measures.Key Concepts addressed:
Sounds great, doesn’t it? Getting clinical trial results quickly has so much going for it. Information sooner! More affordable trials!
Substituting outcomes that can take years, or even decades, to emerge, with ones you can measure much earlier, makes clinical research much simpler. This kind of substitute outcome is called a surrogate (or intermediate) endpoint or outcome.
Surrogates are often biomarkers – biological signs of disease or a risk factor of disease, like cholesterol in the blood. They are used in clinical care to test for, or keep track of, signs of emerging or progressing disease. Sometimes, like cholesterol, they’re the target of treatment.
The problem is, these kinds of substitute measures aren’t always reliable. And sometimes we find that out in the hardest possible way.
The risk was recognized as soon as the current methodology of clinical trials was being developed in the 1950s. A famous statistician who was key to that process, Austin Bradford-Hill, put it bluntly: if the “rate falls, the pulse is steady, and the blood pressure impeccable, we are still not much better off if unfortunately the patient dies.”
That famously happened with some drugs that controlled cardiac arrhythmia – irregular heartbeat that increases the chances of having a heart attack. On the basis of ECG tests that showed the heartbeat was regular, these drugs were prescribed for years before a trial showed that they were causing tens of thousands of premature deaths, not preventing them. That kind of problem has happened too often for comfort.
It happened again this week – although at least before the drug was ever approved. A drug company canceled all its trials for advanced gastric (stomach) cancer of a new drug. The drug is called Rilotumumab. Back in January, it was a “promising” treatment, billed as bringing “new hope in gastric cancer.” It got through the early testing phases and was in Phase III trials – the kind needed to get FDA approval.
But one phase III trial, RILOMET-1, quickly showed an increase in the number of deaths in people using the drug. We don’t know how many yet – but it was enough for the company to decide to end all trials of the substance.
This drug targets a biomarker associated with worse disease outcomes, an area seen by some as transforming gastric cancer research and treatment. Others see considerable challenges, though – and what happened to the participants in the RILOMET-1 trial underscores why.
There is a lot of controversy about surrogate outcomes – and debates about what’s needed to show that an outcome or measure is a valid surrogate we can rely on. They can lead us to think that a treatment is more effective than it really is.
Yet a recent investigative report found that cancer drugs are being increasingly approved based only on surrogate outcomes, like “progression-free survival.” That measures biomarker activity rather than overall survival (when people died).
It can be hard to recognize at first, what’s a surrogate and what’s an actual health outcome. One rule of thumb is, if you need a laboratory test of some kind, it’s more likely to be a surrogate. Whereas symptoms of the disease you’re concerned, or harm caused by the disease, are the direct outcomes of interest. Sometimes those are specified as”patient-relevant outcomes.”
Many surrogate outcomes are incredibly important, of course – viral load for HIV treatment and trials for example. But in general, when clinical research results are based only on surrogates, the evidence just isn’t as strong and reliable as it is for the outcomes we are really concerned about.
Text reproduced from http://statistically-funny.blogspot.co.uk/. Cartoons and text copyright Hilda Bastian, usable under Creative Commons non-commercial license, CC BY-NC-ND 4.0.
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