Stable Disease Is a Valid End Point in Clinical Trials

For most clinical oncologists trained before the 1990s, a 20% or greater response rate is the convention for a drug to be considered active in phase II studies. However, this no longer holds true with several targeted therapies repeatedly achieving the regulatory criteria of progression-free and overall survival benefit with considerably lower objective response rates but a sizeable proportion of patients having stable disease. Considerable skepticism persists as to the value of stable disease as a valid outcome in early clinical trials of new agents. With a high percentage of new oncologic agents failing in phase III studies, the confidence one has in predicting later success in randomized studies when stable disease alone is observed is understandably low. Continued uncertainty of the value of stable disease is based on the lack of precision in defining this as a meaningful outcome. With the term stable disease encompassing a broad range from <20% enlargement to <30% reduction using standard response criteria response evaluation criteria in solid tumors, what one refers to as stable disease is open to diverse interpretation. The evidence that stable disease is a valid end point in many recent clinical trials is therefore discussed in this review and along with contemporary methods that bring some accuracy to the interpretation of stable disease within the context of clinical trial results.