What is Objective Response Rate (ORR) in clinical trials?

Definition

This refers to the proportion of patients who, according to the universally accepted criteria for tumor mitigation, have achieved a pre-established reduction in tumor volume (CR/PR) and can maintain the minimum time requirement. The remission of solid tumors can be complete (Complete Response, CR) or partial (Partial Response, PR), while the assessment of non-solid tumors has some other evaluation criteria.

Position

ORR is an index directly measuring the anti-tumor activity of a drug and is the most common endpoint based on tumor measurements, evaluated in single-arm trials. ORR usually cannot serve as the basis for drug approval, but for some drugs with significant ORR effects or breakthrough drugs, especially those urgently needed in clinical practice, can obtain temporary rapid approval from drug approval authorities through ORR results. Nevertheless, subsequent supplements of PFS or OS results are still required.

Advantages

Typically smaller sample size, shorter follow-up time. The therapeutic effect is attributed to the drug, excluding the natural course of the disease and is usually based on objective and quantitative assessments, making it more suitable for enriched population trials.

Disadvantages

The major downside of ORR is that the ORR effect may not translate into survival benefits. Frequent imaging evaluations are required in the process of assessing ORR, and ORR is not a direct measure of the clinical benefits of the drugs. Further, the use of ORR alone may not adequately describe the anti-tumor activity of the trial drug, hence the need for a concurrent descriptive analysis of the duration of response (i.e., the time from the initial tumor response to disease progression or death from any cause, whichever occurs first) and time to response.