Evidence-Based Assessment and Application of Prognostic Markers: The Long Way from Single Studies to Meta-Analysis

The identification and assessment of prognostic markers constitutes one of the major tasks in clinical research. Despite huge research effort, the prognostic value of most traditional factors under discussion is uncertain and the usefulness of many specific markers, prognostic indices, and classification schemes is still unproven. Results from different studies are often contradictory, and a general assessment of the usefulness of a specific marker is very difficult. One reason is that systematic reviews of prognostic marker studies have received rather little attention in the literature. It is obvious that a clinically useful and sensible systematic review of a prognostic marker is only possible if the published studies reflect the true nature of the marker and if sufficient details are given in each report.