Objective response rate

When used as a clinical endpoint for clinical trials of cancer treatments, this often called the objective response rate (ORR). The FDA definition of ORR is “the proportion of patients with tumor size reduction of a predefined amount and for a minimum time period.”

However, PFS and ORR also have challenges, as determination of response and progression using anatomic imaging techniques may suffer from issues associated with measurement variability and discordance in interpretation between radiologists ¹⁾