Minimally important differences for the EORTC QLQ-C30 in prostate cancer clinical trials.

BACKGROUND: The aim of the study was to estimate the minimally important difference (MID) for interpreting group-level change over time, both within a group and between groups, for the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire Core 30 (EORTC QLQ-C30) scores in patients with prostate cancer. METHODS: We used data from two published EORTC trials. Clinical anchors were selected by strength of correlations with QLQ-C30 scales. In addition, clinicians' input was obtained with regard to plausibility of the selected anchors. The mean change method was applied for interpreting change over time within a group of patients and linear regression models were fitted to estimate MIDs for between-group differences in change over time. Distribution-based estimates were also evaluated. RESULTS: Two clinical anchors were eligible for MID estimation; performance status and the CTCAE diarrhoea domain. MIDs were developed for 7 scales (physical functioning, role functioning, social functioning, pain, fatigue, global quality of life, diarrhoea) and varied by scale and direction (improvement vs deterioration). Within-group MIDs ranged from 4 to 14 points for improvement and - 13 to - 5 points for deterioration and MIDs for between-group differences in change scores ranged from 3 to 13 for improvement and - 10 to - 5 for deterioration. CONCLUSIONS: Our findings aid the meaningful interpretation of changes on a set of EORTC QLQ-C30 scale scores over time, both within and between groups, and for performing more accurate sample size calculations for clinical trials in prostate cancer.

Interpreting European Organisation for Research and Treatment for Cancer Quality of life Questionnaire core 30 scores as minimally importantly different for patients with malignant melanoma.

INTRODUCTION: Health-related quality of life (HRQOL) is increasingly recognised as an important end-point in cancer clinical trials. The concept of minimally important difference (MID) enables interpreting differences and changes in HRQOL scores in terms of clinical meaningfulness. We aimed to estimate MIDs for interpreting group-level change of European Organisation for Research and Treatment for Cancer Quality of life Questionnaire core 30 (EORTC QLQ-C30) scores in patients with malignant melanoma. METHODS: Data were pooled from three published melanoma phase III trials. Anchors relying on clinician's ratings, e.g. performance status, were selected using correlation strength and clinical plausibility of associating the anchor/EORTC QLQ-C30 scale pair. HRQOL change was evaluated between time periods that were common to all trials: start of treatment to end of treatment and end of treatment to end of follow-up. Three change status groups were formed: deteriorated by one anchor category, improved by one anchor category and no change. Patients with greater anchor change were excluded. The mean change method and linear regression were used to estimate MIDs for change in HRQOL scores within the group and between the groups of patients, respectively. RESULTS: MIDs varied according to QLQ-C30 scale, direction (improvement versus deterioration), anchor and period. MIDs for within-group change ranged from 4 to 18 points (improvement) and -16 to -4 points (deterioration), and MIDs for between-group change ranged from 3 to 16 points and from -16 to -3 points. MIDs for most of QLQ-C30 scales ranged from 5 to 10 points in absolute values. CONCLUSIONS: These results are useful for interpreting changes in EORTC QLQ-C30 scores over time and for performing more accurate sample size calculations in adjuvant melanoma settings.