Key factors in evaluating potential clinical biomarkers.

Clinical biomarkers have important differences from exploratory or experimental biomarkers. The introduction of biomarkers into a true clinical situation requires unique considerations of the potential utility of the markers. In contrast to experimental situations in which various parameters can be tightly controlled, the world of patient care can be characterized as the 'Wild West' - an unknown frontier in which every possible variable may be introduced at some stage. Because a clinical biomarker or pattern of biomarkers arises from a single individual without the benefit of a control group to detect inconsistent sample handling, the biomarker must be, above all else, robust. A biomarker for which even slightly different handling in the clinic results in highly different assay results will have minimal utility, and may even create a dangerous situation for patients. The samples and assays used, the clinical situation and the format of data output are also important considerations in the development of clinical biomarkers.