M easuring changes in tumor size with imaging can help determine if patients are responding to therapy, as well as if and when disease progression occurs. In the clinical trial setting, there is blending of patient care and scientific discovery. Quantification of radiologic changes in tumor size extends beyond contributing to individual patient treatment decisions. It can also provide a method to perform statistical analyses and attain regulatory drug approval of promising investigational therapeutic agents by objective clinical trial endpoints. Image-based treatment outcome measures are commonly used to assess if treatments are effective and, in the past few decades, have played an increasing role in the regulatory drug approval of a growing number of oncologic therapies. Therefore, it is imperative that the imaging community understands the application of these rule-based response criteria during image interpretation and how reported findings inform clinical trial results.
Oncology Innovation: Drug Development ProcessThe drug discovery and approval paradigm is a very timeand resource-intensive process. For U.S. Food and Drug Administration (FDA) approval of one therapy, typically anywhere between 5000 to 10 000 initial compounds are rigorously investigated in a structured process that usually takes more than $1 billion and 10 years to complete (2-4). Beyond the initial concept and basic drug development, promising agents must undergo extensive preclinical evaluation and endure multiple phases of clinical trials to ensure safety and efficacy. Preclinical testing is performed both in This copy is for personal use only. To order printed copies, contact reprints@rsna.org Drug discovery and approval in oncology is mediated by the use of imaging to evaluate drug efficacy in clinical trials. Imaging is performed while patients receive therapy to evaluate their response to treatment. Response criteria, specifically Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST 1.1), are standardized and can be used at different time points to classify response into the categories of complete response, partial response, stable disease, or disease progression. At the trial level, categorical responses for all patients are summated into image-based trial endpoints. These outcome measures, including objective response rate (ORR) and progression-free survival (PFS), are characteristics that can be derived from imaging and can be used as surrogates for overall survival (OS). Similar to OS, ORR and PFS describe the efficacy of a drug. U.S. Food and Drug Administration (FDA) regulatory approval requires therapies to demonstrate direct evidence of clinical benefit, such as improved OS. However, multiple programs have been created to expedite drug approval for life-threatening illnesses, including advanced cancer. ORR and PFS have been accepted by the FDA as adequate predictors of OS on which to base drug approval decisions, thus substantially shortening the time and cost of drug development (1). Use of imaging surrogate marke...