Quality of life (QOL) is frequently an endpoint in clinical trials involving patients with advanced cancer. Statistical significance of minimal differences can be achieved with sufficient sample size, yet the actual clinical relevance is unknown. The purpose of this study was to establish the minimal clinically important difference (MCID) for the European Organisation for Research and Treatment of Cancer (EORTC) bone metastases module (EORTC QLQ-BM22).

Patients with bone metastases across seven countries were prospectively enrolled in a trial validating the EORTC QLQ-BM22 and completed the QLQ-BM22 and core measure (QLQ-C30) at baseline and 1-month follow-up. MCIDs were calculated for each QOL scale for both improvement and deterioration using both an anchor- (performance status) and distribution-based approach.

A total of 93 patients completed both baseline and follow-up QOL and had recorded performance status at both intervals. Statistically significant meaningful differences were seen in seven scales. There were improvements of 30.5 (95 % confidence interval, 9.0 to 52.0), 20.1 (7.1 to 33.2), 30.5 (13.8 to 47.3) and 19.6 (5.0 to 34.3) in the pain, painful site, painful characteristic and functional interference scales, respectively, demonstrated clinical relevance. Decreases of 12.4 (0.3 to 24.6), 22.4 (11.8 to 32.9) and 13.5 (1.9 to 25.1) were required to represent clinically relevant deterioration in emotional functioning, global health status and financial issues, respectively. Minimal differences for improvement were closest to 0.5 standard deviations (SD) while for deterioration, closer to 0.3 SD on the QLQ-BM22.

Identification of requirements for clinical significance can assist in determining the relevance of QOL changes after treatment and in sample size determination in future trials. Our study is limited by the small sample size. Future studies should continue to determine MCID and confirm our findings using a variety of appropriate anchors and in a larger sample.