Response Rate — What It Means in Clinical Trials
Plain English Definition
Response rate (also called objective response rate or ORR) is the percentage of participants whose tumors shrank by a meaningful amount during treatment. A response can be complete (tumor disappeared) or partial (tumor shrank by at least 30%). Response rate tells you how likely the treatment is to shrink your tumor.
Why It Matters
A higher response rate means more people saw their tumors shrink. But response rate alone does not tell you how long the response lasts or whether it extends life — those are measured by duration of response and overall survival.
Example
A trial might report: "Overall response rate was 45% (12% complete response, 33% partial response)." This means nearly half of participants had meaningful tumor shrinkage.
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