# A core outcome set for locoregional treatment reporting in neoadjuvant systemic breast cancer treatment trials

## TL;DR

This paper introduces a standardized set of outcomes for reporting locoregional breast cancer treatments after neoadjuvant therapy to improve trial consistency and quality.

## Contribution

A novel core outcome set was developed to standardize locoregional treatment reporting in breast cancer trials following neoadjuvant therapy.

## Key findings

- 159 locoregional outcomes were classified into 101 domains for stakeholder prioritization.
- A 15-item core outcome set was finalized through a Delphi survey and consensus meeting involving 470 international professionals.
- The COS includes pre-treatment surgical plans, surgical details, and radiation therapy specifics.

## Abstract

Accurate information about locoregional breast cancer treatments following neoadjuvant systemic therapy (NST) is essential for meaningful interpretation of oncological outcomes but reporting is currently poor. We developed a core outcome set (COS) to improve the quality and consistency of locoregional outcome reporting in breast cancer NST trials. The COS was developed in three phases according to COS-STAD guidance, with the generation of a list of relevant outcome domains, prioritisation of outcomes through two rounds of an international online multi-stakeholder Delphi survey and a consensus meeting. 159 unique locoregional outcomes were classified into 101 outcome domains for inclusion in the Delphi survey, which was completed by 470 international professionals. The final 15-item COS, which included the pre-NST surgical plan, details of surgery performed following completion of treatment and details of radiation therapy, was agreed at an in-person consensus meeting. Widespread COS implementation will improve the quality and value of future NST trials.