Objectives/purpose: Following the release of the US Food and Drug Administration (FDA) Guidance on core patient-reported outcomes in cancer clinical trials, there has been growing interest in using single items to measure treatment tolerability from the patient’s perspective. The FDA Guidance specifically mentions item Q168 “To what extent have you been troubled with side-effects from your treatment” from the European Organisation for Research and Treatment of Cancer (EORTC) Item Library. This study aims to evaluate the psychometric properties of item Q168 in a diverse sample of cancer patients.
Sample and settings: This was a multi-national, online panel study that collected cross-sectional Q168 and EORTC QLQ-C30 data from a sample of 2,643 cancer patients, recruited from 11 countries.
Procedures: Psychometric analyses of item Q168 included: (1) convergent validity by examining correlations between item Q168 and Global Health Status/Quality-of-Life, (2) known-groups validity by examining item Q168 responses based on clinical characteristics of participants, and (3) differential item functioning (DIF) by examining the performance of item Q168 in subgroups of participants.
Results: Patients had a mean age of 58 years (range 18 to 92) and equal gender distribution. All major cancer types were represented, with the most common being breast (21%) and prostate cancer (14%). Convergent validity was evidenced by a moderate, negative correlation (rpolyserial=−0.37) between Q168 and Global Health Status/QOL. Known groups validity was evidenced by significant differences in Q168 responses between predefined clinical groups (p < 0.001). DIF analyses are ongoing and results will be presented at COSA-IPOS 2025.
Conclusion and clinical implications: Following the release of the FDA guidance and the launch of the EORTC Item Library, this study provides an evidence-based rationale for using a single-item measure of side effect burden, such as EORTC item Q168, both within cancer clinical trials and as part of routine care.