Abstract PS4-10-03: Programmed cell death ligand 1 (PD-L1) expression profiles of early-stage triple-negative breast cancer (TNBC) in China: a retrospective observational study

Abstract Background The incidence and mortality of breast cancer (BC) in China are expected to rise to nearly 400,000 new cases and nearly 90,000 deaths annually by 2030, with TNBC accounting for 10-20%. Immune checkpoint inhibitors, including the programmed cell death 1 (PD-1) inhibitor, pembrolizumab, are approved for treating early TNBC (PD-L1 CPS ≥20) in China. However, data on the profiles of PD-L1 expression in Chinese patients (pts) with early-stage TNBC remain limited. Objectives To determine the prevalence of PD-L1 expression in Chinese pts with early-stage TNBC and to assess its correlation with clinicopathological characteristics. Methods This observational, retrospective study, conducted across five centers in China, included female adult pts with early stage (American Joint Committee on Cancer [AJCC] IIA-IIIB) TNBC. Eligible pts had a biopsy or surgical specimen available for PD-L1 testing, and had received no prior systemic therapy for TNBC, with no treatment received within the past 3 years. Newly obtained specimens were defined as tissue collected ≤90 days prior to PD-L1 testing; archival specimens were formalin fixed, paraffin embedded specimens collected by resection or core needle biopsy and were ≤3 years old. PD-L1 expression was evaluated at pathology laboratories of each hospital with the PD-L1 immunohistochemistry (IHC) 22C3 pharmDx assay (Agilent Technologies, CA, USA) performed on the Dako ASL48 platform. PD-L1 expression was reported as a combined positive score (CPS), whereby a score ≥1 was positive and