Minimal clinically important differences in the EORTC QLQ-C30 and brief pain inventory in patients undergoing re-irradiation for painful bone metastases
The EORTC QLQ-C30 and the Brief Pain Inventory (BPI) are validated tools for measuring quality of life (QOL) and the impact of pain in patients with advanced cancer. Interpretation of these instrument scores can be challenging and it is difficult to know what numerical changes translate to clinically significant impact in patients’ lives. To address this issue, our study sought to establish the minimal clinically important differences (MCID) for these two instruments in a prospective cohort of patients with advanced cancer and painful bone metastases.
Both anchor-based and distribution-based methods were used to estimate the MCID scores from patients enrolled in a randomized phase III trial evaluating two different re-irradiation treatment schedules. For the anchor-based method, the global QOL item from the QLQ-C30 was chosen as the anchor. Spearman correlation coefficients were calculated for all items and only those items with moderate or better correlation (|r| ≥ 0.30) with the anchor were used for subsequent analysis. A 10-point difference in the global QOL score was used to classify improvement and deterioration, and the MCID scores were calculated for each of these categories. These results were compared with scores obtained by the distribution-method, which estimates the MCID purely from the statistical characteristics of the sample population.
A total of 375 patients were included in this study with documented pain responses and completed QOL questionnaires at 2 months. 9/14 items in the QLQ-C30 and 6/10 items in the BPI were found to have moderate or better correlation with the anchor. For deterioration, statistically significant MCID scores were found in all items of the QLQ-C30 and BPI. For improvement, statistically significant MCID scores were found in 7/9 items of the QLQ-C30 and 2/6 items of the BPI. The MCID scores for deterioration were uniformly higher than the MCIDs for improvement. Using the distribution-based method, there was good agreement between the 0.5 standard deviation (SD) values and anchor-based scores for deterioration. For improvement, there was less agreement and the anchor-based scores were lower than the 0.5 SD values obtained from the distribution-based method.
We present MCID scores for the QLQ-C30 and BPI instruments obtained from a large cohort of patients with advanced cancer undergoing re-irradiation for painful bone metastases. The results from this study were compared to other similar studies which showed larger MCID scores for improvement compared to deterioration. We hypothesize that disease trajectory and patient expectations are important factors in understanding the contrasting results. The results of this study can guide clinicians and researchers in the interpretation of these instruments.
KeywordsBone metastases Radiation Minimal clinically important differences EORTC QLQ-C30 Brief pain inventory
We thank all investigators, clinical research assistants, and patients for participation in this study coordinated by the NCIC Clinical Trials Group. This study was supported by the NCIC CTG’s programmatic grants from the Canadian Cancer Society Research Institute; the RTOG grant U10 CA21661 and CCOP grant U10 CA37422 from the National Cancer Institute in the US. Funding for Australia & New Zealand was from Cancer Council Australia (Grant for International Infrastructure Support) and Royal Adelaide Hospital (Special Purposes Fund Research Grant). The Dutch Cancer Society funded the national data management for Dutch patients (Dutch Cancer Society; CKTO 2004-06). Funding for the French investigators was from Assistance Publique-Hopitaux de Paris.
This study was funded by the NCIC CTG’s programmatic grants from the Canadian Cancer Society Research Institute and other sources as detailed above.
Compliance with ethical standards
Conflict of interest
There are no conflicts of interest to declare for all authors.
Ethical approval for research involving human participants
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Acceptable principles of ethical and professional conduct were followed, and research ethics board approval was obtained at all participating institutions.
Informed consent was obtained from all individual participants included in the study.
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