45P Improved concordance between pathology laboratories using Ki67 global scoring: Real-world data from two large breast centers in Sweden
Ceren Boyacı, Wenwen Sun, J. Hartman, Balázs Ács · ESMO Open · 2025
Ki67 is a broadly available biomarker of proliferation with various approaches to its evaluation in breast cancer. The International Ki67 in Breast Cancer Working Group (IKWG) recommends calculating Ki67 globally across the tumor area, as this method offers high interobserver concordance. These recommendations have been integrated in many international breast cancer guidelines (ASCO, ESMO), yet there is no real-world data on if it improved inter-pathologists and inter-laboratory variability. Here, we present the first real-world data on the variability and impact of Ki67 scores on clinical decision-making in breast cancer when using hotspot scoring and after implementing IKWG global scoring method in clinical practice.