Proposal for standardized definitions for efficacy end points in adjuvant breast cancer trials: the STEEP system

Purpose: Standardized definitions of breast cancer clinical trial end points must be adopted to permit the consistent interpretation and analysis of breast cancer clinical trials and to facilitate cross-trial comparisons and meta-analyses. Standardizing terms will allow for uniformity in data collection across studies, which will optimize clinical trial utility and efficiency. A given end point term (eg, overall survival) used in a breast cancer trial should always encompass the same set of events (eg, death attributable to breast cancer, death attributable to cause other than breast cancer, death from unknown cause), and, in turn, each event within that end point should be commonly defined across end points and studies.

Methods: A panel of experts in breast cancer clinical trials representing medical oncology, biostatistics, and correlative science convened to formulate standard definitions and address the confusion that nonstandard definitions of widely used end point terms for a breast cancer clinical trial can generate. We propose standard definitions for efficacy end points and events in early-stage adjuvant breast cancer clinical trials. In some cases, it is expected that the standard end points may not address a specific trial question, so that modified or customized end points would need to be prospectively defined and consistently used.

Conclusion: The use of the proposed common end point definitions will facilitate interpretation of trial outcomes. This approach may be adopted to develop standard outcome definitions for use in trials involving other cancer sites.