The Programmed Cell Death Ligand 1 and Lipocalin 2 Expressions in Primary Breast Cancer and Their Associations with Molecular Subtypes and Prognostic Factors

Purpose: Breast cancers exhibit molecular heterogeneity, leading to diverse clinical outcomes and therapeutic responses. Immune checkpoint inhibitors targeting PD-L1 have shown promise in various malignancies, including breast cancer. Lipocalin 2 (LCN2) has also been associated with tumor aggressiveness and prognostic potential in breast cancers. However, the expression of PD-L1 and LCN2 in breast cancer subtypes and their prognostic implications remains poorly investigated. Methods: A retrospective analysis of 89 primary breast cancer cases was conducted to assess PD-L1 and LCN2 expressions using immunohistochemistry. Cases were classified into four different molecular subtypes based on ER, PR, HER2, and Ki-67 status. Associations between PD-L1 and LCN2 expressions and various prognostic factors were examined. Results: Although low expression of LCN2 (Allred score of <3) was observed even in normal breast tissue, LCN2 expression with increasing Allred score (≥3) positively correlated with the histological grade, high Ki-67 proliferation index, and ER/PR negativity. Significant elevations of LCN2 and PD-L1 expressions were observed in triple-negative and HER2-positive breast cancers. Conclusion: The results of the study highlight the association of LCN2 with known prognostic factors and molecular subtypes. To identify potential immunotherapy recipients, it would be useful to evaluate LCN2 as well as PD-L1 immune targets in different subgroups of breast cancer patients. Further studies with larger patient numbers are warranted to validate these observations and establish standardized scoring criteria for LCN2 expression assessment.