# The COMBAT Project: study protocol for the development of a core outcome set for morbidity following surgery in paediatric brain tumour patients

## TL;DR

The COMBAT Project aims to create a standardized set of outcomes to measure and report post-surgery complications in children with brain tumors, improving consistency and comparison across studies.

## Contribution

The study introduces a core outcome set for postoperative morbidity in pediatric brain tumor surgery, addressing inconsistent reporting practices.

## Key findings

- A systematic review will identify reported adverse outcomes and their measurement methods.
- Patient and carer perspectives will be gathered through qualitative interviews to inform outcome selection.
- A two-round eDelphi survey and international consensus meeting will finalize the core outcome set.

## Abstract

Central nervous system tumours affecting the brain and spine are the most common solid tumour site in the paediatric population and the most common causes of cancer death in children and young people. They are associated with high morbidity both from the tumour and the interventions used to treat them. Postoperative morbidity reporting following surgery for paediatric brain tumours is poor. This is due to variability of outcomes measured and reported and the lack of a common language when reporting adverse outcomes. One solution is to develop a core outcome set which will stipulate the minimum postoperative outcomes that should be reported. The COMBAT (Core Postoperative Morbidity Set for Paediatric Brain Tumours) Project will develop a core set of adverse outcomes that can be applied to paediatric brain tumour patients undergoing surgery.

This protocol has been developed using the COS-STAD (Core Outcome Set-Standards for Development) recommendations and the COS-STAP (Core Outcome Set-STAndardised Protocol Items) statement. A systematic review will identify adverse outcomes reported in the literature and how they are measured. Outcomes of importance to patients and their carers will be identified from semi-structured qualitative interviews with patients and their carers from Alder Hey Children’s Hospital, Liverpool, UK. Consensus on the most important harms will be sought using a two-round eDelphi survey completed by national and international participants including health professionals, researchers, patients and their carers. Results of the eDelphi survey will be assessed against a pre-defined definition of consensus and discussed at an international consensus meeting attended by participants of the eDelphi survey.

There is a clear need for a common language to harmonise measurement and reporting of morbidity following surgery for paediatric brain tumour patients. This project will define postoperative adverse outcomes that are of critical importance to key stakeholders. It will standardise surgical morbidity outcome measurement and reporting in both research studies and routine clinical practice, enabling comparison across different trials, studies and clinical services. It will lay the groundwork for future research in paediatric brain tumour surgical morbidity.

This study is registered with the COMET database as Study 1968 (https://www.comet-initiative.org/Studies/Details/1968), registration date: 26/10/2021.

The online version contains supplementary material available at 10.1186/s13063-025-09004-4.