Synthesis of minimally important differences for interpreting EORTC QLQ-C30 change scores across nine cancer types

Brussels, 30 May 2023 – The European Organisation for Research and Treatment of Cancer (EORTC) welcomes the publication of a synthesis of minimally important differences (MIDs)1 that aimed to identify patterns for interpreting group-level change in EORTC QLQ-C30 scores across nine cancer types.

Over the past few years, there has been an increase in the use of patient-reported outcomes (PROs) in cancer clinical trials. Consequently, increasing efforts have been made to develop various standards to improve, among others, the collection, reporting, analysis and interpretation of PRO data in cancer clinical trials. This paper focused on interpretation guidelines for the EORTC QLQ-C30 based on MIDs.

What is a minimally important difference (MID) and how is it useful in clinical research?

Simply put, MID is the smallest change in a PRO score which patients perceive as important. MIDs help to attach meaningful interpretations to PRO results from clinical trials and aid to inform sample size calculations for new studies with PRO endpoints.

Dr Jammbe Musoro, from the EORTC and lead author of the paper, highlights that: “This study brings together MIDs for group-level interpretation of EORTC QLQ-C30 change scores over time across multiple cancer types. To date, this is the most comprehensive scrutiny of MID commonalities and differences for the EORTC QLQ-C30 across different cancer types by scale, direction of change (improvement vs deterioration) as well as for within vs between group comparisons.”

About the study by Musoro et al.

The study analysed data from 21 published EORTC Phase III trials that enrolled 13,015 patients across nine cancer types: brain, colorectal, advanced breast, head/neck, lung, mesothelioma, melanoma, ovarian, and prostate.

As Corneel Coens, from the EORTC and co-author of the paper, points out: “Our study shows that MIDs varied by scale and by cancer type; but also whether the change was an improvement or deterioration and whether the difference was within or between groups of patients. Hence, researchers applying simple rules of thumb must be aware they may miss relevant changes or underpower analyses when smaller MIDs apply.”

Prof. Mirjam Sprangers, from the University of Amsterdam and the Cancer Center Amsterdam, and co-author of the paper, adds that: “This research is part of an ongoing EORTC Quality of Life Group strategy to develop pragmatic and evidence-based guidelines for interpreting the EORTC QLQ-C30. These findings supplement existing work to build more robust MID guidelines for interpreting QLQ-C30 change scores in clinical trials. Interestingly, our results are consistent with recent guidelines that reinforce the fact that no single MID can be applied for all QLQ-C30 scales and across various cancer types. Our paper presents a diverse range of MIDs to help interpretation and inform more accurate sample size calculations for clinical trials with EORTC QLQ-C30 endpoints.”


The European Organisation for Research and Treatment of Cancer (EORTC) is a non-governmental, non-profit organisation, which unites clinical cancer research experts, throughout Europe, to define better treatments for cancer patients to prolong survival and improve quality of life. Spanning from translational to large, prospective, multi-centre, phase III clinical trials that evaluate new therapies and treatment strategies as well as patient quality of life, its activities are coordinated from EORTC Headquarters, a unique international clinical research infrastructure, based in Brussels, Belgium.

About the Quality of Life Group

The Quality of Life Group (QLG) strives to improve health-related quality of life (HRQoL) of cancer patients, through dedicated research and the use of HRQoL measures within cancer clinical trials and clinical practice. HRQoL constitutes an important aspect of cancer research and care: it gives a voice to patients, putting their experience at the forefront. The QLG is part of the European Organisation for Research and Treatment of Cancer (EORTC).
For further information, please visit the QLG website.


Caroline Hance (EORTC QLG)
Strategic Lead Communication

1 Musoro ZJ, Coens C, Sprangers M.A.G. et al. Minimally important differences for interpreting EORTC QLQ-C30 change scores over time: A synthesis across 21 clinical trials involving nine different cancer types. Eur J Cancer 2023;188:171-82.

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