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 1 was negative. Data in medical records were used. For group comparisons (positive vs. negative), P values were calculated using a two-sided t-test or Wilcoxon rank sum test for continuous variables, a two-sided Pearson’s Chi-square test or Fisher’s exact test (if ≥25% cells had expected counts 5) for categorical variables, and a two-sided Wicoxon rank sum test for ordinal variables. 95% confidence intervals were calculated using the Clopper-Pearson method. Results In total, 300 patients were included, of whom 296 had evaluable samples. The median age at diagnosis was 54 years; 181 pts (61%) were postmenopausal. The majority of pts (n=255; 86%) had no family history of TNBC; family history was present in 13 (4%) and unknown in 28 (9%). Archival tissue was used in 292 (99%) cases, while newly obtained tissue was used in 4 (1%); specimens included resections (215 pts 73%) and biopsies (81 pts 27%). PD-L1 positivity was observed in 81% of evaluable pts, with CPS scores distributed as follows: 1 in 56 (19%), 1-10 in 106 (36%), 10-20 in 48 (16%), and ≥20 in 86 (29%). Compared with CPS-negative pts, CPS-positive pts had a younger age at diagnosis (median Q1-Q3, 53 45-61 vs 58 49-66 years; p=0.0192) and had higher Ki-67 expression (median Q1-Q3 expression, 70% 60%-80% vs. 50% 25%-70%; p=0.0001). No statistically significant difference between CPS-positive and -negative groups was found in menopausal status (pre/postmenopausal), family history, primary tumor site (left/right/bilateral), grade (well/moderately/poorly differentiated), stage at initial diagnosis, Eastern Cooperative Oncology Group (ECOG) status (0/1), specimen type (biopsy/resection), germline BRCA mutation (pathogenic/uncertain/benign). Conclusions This observational, retrospective study provides important data on the characteristics of pts with early stage TNBC in China, including the prevalence of PD-L1 expression, and its association with clinicopathological features. Citation Format: M. Shen, L. Liu, Y. Liu, S. Zhou, Y. Ding, D. Lin, R. Luo, H. Bu, J. Liu, J. Wang, L. Wang, Y. Liu, W. Yang. Programmed cell death ligand 1 (PD-L1) expression profiles of early-stage triple-negative breast cancer (TNBC) in China: a retrospective observational study abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS4-10-03.