CD274 and breast carcinoma: 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).