The use of EORTC QLQ-C30 Summary Score in cancer research and its performance as compared with the EORTC QLQ-C30 Global Health/Quality of Life scale: A systematic review and comparative analysis of effect sizes

BACKGROUND: The EORTC QLQ-C30 Summary Score (Summary Score) measures overall health-related quality of life (HRQoL) using 27 of the 30 items of the EORTC QLQ-C30. This systematic review evaluated the Summary Score's use in clinical oncology studies, its construct validity through cross-sectional known-group comparisons, and its responsiveness to change over time compared to the EORTC QLQ-C30 Global Health/Quality of Life (Global Health/QoL) scale. METHODS: We systematically searched 11 databases for original studies on the Summary Score in adult cancer patients up to April 2024. Data were extracted and cross-checked by two reviewers. We analyzed Cohen's d effect sizes from cross-sectional known-group comparisons and responsiveness analyses of both the Summary Score and Global Health/QoL scale, using a Bland-Altman plot, paired t-tests, and a linear mixed-effects model. RESULTS: A total of 249 studies were included, with 37 % using the Summary Score as a primary patient-reported outcome measure. Only 4 studies formally validated the Summary Score; most employed it to assess HRQoL for varied purposes. Across 29 comparisons from 18 studies, the Summary Score yielded higher effect sizes than the Global Health/QoL scale, confirmed by the mixed-effects model (mean absolute difference = 0.17, p = 0.018). In paired t-tests, this difference was 0.21 (95 % CI 0.04 - 0.38) in cross-sectional known-group comparisons, and 0.07 (95 % CI -0.16 - 0.29) and 0.23 (95 % CI -0.30 - 0.76) for responsiveness within and between groups, respectively. CONCLUSION: This study indicates that the Summary Score more effectively detects differences in HRQoL than the Global Health/QoL scale. This advantage was most evident in cross-sectional known-group comparisons and, to a lesser extent, in analyses of responsiveness to change between groups. Based on the available evidence, we recommend the Summary Score for assessing overall HRQoL in clinical oncology studies, unless there is a specific, predefined rationale for selecting the Global Health/QoL scale.