[Surrogate markers--substitute measurements. Easy to measure but irrelevant?]

Many treatments aim at making a patient feel better due to symptom relief or improved quality of life. Other treatments are given in order to prevent future complications, non-fatal or fatal. There are methodological difficulties in assessing subjective symptoms and quality of life. To document reduced risk of complications takes large, long-term, costly clinical trials. Thus, the use of a surrogate marker to document benefit may seem appealing. A well-validated surrogate marker can demonstrate benefit of a given treatment with fewer patients in a shorter time and at considerably lower cost. It is much easier to show in a 12-week study that a new compound lowers blood pressure than to show that it lowers the risk of stroke, myocardial infarction or renal impairment. One problem with surrogate markers is that very few are well-validated, another is that even those which are cannot be expected to reflect adverse effects, expected or unexpected, and are thus of limited value in the global assessment of benefit vs. risk. It is recommended that results obtained with surrogate markers be regarded as preliminary until results of large trials with clinically relevant outcomes are available.