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.