Anti‐Unicorn Principle: Appropriate Biomarkers Don't Need to Be Rare or Hard to Find

The emphasis on biomarkers as a new approach often has lead to expectations that the ideal biomarker must be novel and/or exotic. To answer the pertinent questions during drug development, teams often embark on the quest for the “unicorn” of biomarkers, sometimes resulting in the best and most practical test being overlooked as the search progresses for elusive methods. This article highlights examples of unicorn, horse, and mule biomarker approaches. Keywords: biomarkers; drug development; chronic myeloid leukemia (CML); pharmacogenetics; anticancer drug