Surrogate endpoint

In clinical trials, a surrogate endpoint is a measure of effect of a certain treatment that may correlate with a real endpoint but doesn't necessarily have a guaranteed relationship. The National Institutes of Health (USA) define surrogate endpoints as: "A biomarker intended to substitute for a clinical endpoint".^[1]

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In many settings, the primary clinical endpoint takes large, long term trials, which are, obviously expensive. The use of surrogate endpoints can also potentially prevernt otherwise undesired endpoints - death, for example.

It is a major issue in testing the efficacy of medication. For example, most cholesterol-lowering drugs (e.g. the statins) are used to control cardiovascular disease, yet they were introduced with only information on their capacity to decrease cholesterol levels. While elevated cholesterol levels increase the likelihood for heart disease, the relationship is not linear - many people with normal cholesterol develop heart disease, and many with high cholesterol do not. In the case of simvastatin (Zocor®), proof of its efficacy in reducing cardiovascular disease was only presented five years after its original introduction, and then only for secondary prevention. In another case, AstraZeneca has been accused of marketing rosuvastatin (Crestor®) without providing hard endpoint data, relying instead on surrogate endpoints. The company counters that it had been tested on larger groups of patients than any other drug in the class, and that its effects should be comparable to the other statins.

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