editorial On the Quantitative Assessment of Predictive Biomarkers

Predictive biomarkers are among the most direct steps towards converting precision medicine into a clinical reality. By their very definition they are fundamentally different from prognostic or diagnostic biomarkers—instead of helping identify individuals who will develop the disease, they focus on differentiating between those who will and will not “benefit ” from treatment. Given this difference, a natural question is whether the performance met-rics of sensitivity, specificity, positive predictive values (PPVs), and negative predictive values (NPVs) (“four metrics”) used in the prog-nostic/diagnostic context should be extended to the predictive set-ting. The two brief communications published in this issue of the Journal approach the question from two different perspectives. Using methods and assumptions similar to those adopted by Zhang et al. (1), Simon (2) presents simple formulas for esti-mating the four metrics, where the goal is predicting “benefit