METHODS: A total of 121 patients with breast cancer who underwent PD-L1 testing were retrospectively included, comprising 81 patients from Tianjin Medical University Cancer Institute & Hospital (development cohort, April 2023–September 2024) and 40 patients from the First Affiliated Hospital of Bengbu Medical University (external test cohort, January 2019–March 2025). This evidence concerns the gene CD274 and breast cancer.