Evaluation of Programmed Death-ligand 1 Protein Expression in Primary Breast Carcinoma – An Immunohistochemical Study

Introduction: Breast cancer is a biologically heterogeneous malignancy and a major public health concern in India. Programmed death-ligand 1 (PD-L1) has emerged as a key immune checkpoint molecule implicated in tumor immune evasion, with potential predictive value for immunotherapy. Data on PD-L1 expression among breast cancer patients in India remain limited. This study aimed to assess PD-L1 expression in invasive breast carcinoma in an Indian cohort and its association with clinicopathological features. Materials and Methods: A retrospective observational study was carried out on 107 patients with histologically confirmed invasive breast carcinoma at a tertiary care center in Tamil Nadu over 2 years. Tumor histology, grade, lymphovascular invasion, nodal status, and molecular subtype were assessed. Immunohistochemistry for PD-L1 (RBT-PD-L1 rabbit monoclonal antibody), estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), and Ki-67 was performed. PD-L1 expression was evaluated using the RBT-PD-L1 clone (BioSB, USA); ≥1% membranous staining was considered positive. Associations between PD-L1 expression and clinicopathological parameters were analyzed using Chi-square or Fisher’s exact tests. Results: PD-L1 expression was observed in 39.3% of tumor cells and 52.3% of tumor-infiltrating lymphocytes. Significant correlations were noted between PD-L1 positivity and ER negativity ( P = 0.048), nodal metastasis ( P = 0.038), and molecular subtype, with the highest expression in HER2-enriched (55.6%) and basal-like tumors (46.4%). No significant association was observed with age, PR status, HER2 status alone, Ki-67 index, tumor grade, or pathological stage. Conclusion: PD-L1 is frequently expressed in Indian breast cancers, particularly in ER-negative, node-positive, basal-like, and HER2-enriched subtypes. These findings support the potential role of PD-L1 as a biomarker for immune checkpoint therapy in this population and highlight the importance of region-specific profiling to guide immunotherapy strategies.