Surrogacy Case Study: Prostate Specific Antigen (PSA ... - Isped

Surrogate endpoint
• An outcome measure that is assessed earlier, more
frequently or more easily than the final endpoint
• That is “reasonably likely” to predict the eventual
treatment benefit on the definitive endpoint
(survival) (FDA definition)
• Requires correlation between treatment effects on the
marker and on the true endpoint, across groups of
patients
• Prostate-specific antigen (PSA)
• PSA changes are indicators of disease evolution
• 50% PSA decrease (“response”)
• PSA increase (“progression”)