Surrogate markers in clinical trials--challenges and opportunities

Surrogate markers have recently come under scrutiny since a few of the considered most reliable intermediate endpoints (LDL-c, HDL-c and HbA(1c)) have failed to predict clinical benefit following pharmacological intervention in the causal pathway. However, it follows that comprehending the pathophysiological complexity of atherosclerotic vascular disease, no single surrogate is likely to be omniscient in the translation of benefit or harm of a certain therapy. Especially surrogates that are assessed in the circulation merely reflect a part of the complex multipathway disease. Such markers do not have the ability to monitor potential side effects of interventions or assess the activation of unknown pro-atherogenic pathways. Contrary to such soluble endpoints, vascular imaging data can provide information on atherosclerosis as a continuous variable, since the disease process of the vascular wall itself is assessed. Understanding this continuity from the earliest stages through to the vascular complications is essential, as the arterial wall reflects the net effect of either known or yet to be discovered hereditary as well as environmental factors. In this review we will focus on challenges and pitfalls using plasma biomarkers as surrogate endpoints for the assessment of cardiovascular drug efficacy. Subsequently, we will focus on vascular imaging modalities as tools to investigate atherosclerosis.