Abstract 9: Immunohistochemical Profiling of the Tumor Microenvironment in Ethiopian Breast Cancer Tissue: Insights into Pathology and Subtypes

Abstract Purpose: Breast cancer is the leading cause of death among women globally and poses a significant public health challenge in Africa, particularly in Ethiopia. It is important to enhance the effort of immunotherapy development in breast cancer treatment by profiling tumor-infiltrating lymphocytes, tumor-associated macrophages, and PD-L1, along with their relationships to breast cancer subtypes and clinicopathological features. Methods: Formalin-fixed paraffin-embedded (FFPE) tissue blocks (n=81) were collected to analyze tumor-infiltrating lymphocytes, tumor-associated macrophages, and PD-L1 in breast cancer. Immunohistochemistry (IHC) staining was performed to evaluate the expression of these biomarkers. Statistical analysis was conducted using GraphPad Prism version 8. 0. 0. Results: The non-luminal breast cancer subtypes (triple-negative and HER2+) demonstrated a significantly higher proportion of stromal CD20+ tumor-infiltrating lymphocytes (P=0. 0224), intratumoral CD3+ tumor-infiltrating lymphocytes (P=0. 0069), and CD68+ tumor-associated macrophages (P=0. 0223) than the luminal subtypes (Figure 1). Moreover, stromal PD-L1+ expression (P=0. 0280), intratumoral PD-L1+ expression (P=0. 0232), intratumoral CD3+ tumor-infiltrating lymphocytes (P=0. 0222), and intratumoral CD163+ tumor-associated macrophages (P=0. 0138) were significantly higher in grade III breast cancer compared to grades II and I. Conclusion: Infiltrating immune cells were more common in hormone receptor-negative and higher-grade breast cancers, suggesting their role in tumor aggression and poorer prognosis. Citation Format: Esmael B. Besufikad, Adey Feleke Desta, Dareskedar Tsehay Sewasew, Marcus Bauer, Bethelehem Nigussie, Menal Hassen, Melisachew Mulatu Yeshi, Alemwosen TeklehaymanotAlem, Sofia Yimam, Betelhem Getachew, Selfu Girma, Eva J. Kantelhardt, Tesfaye Sisay Tessema, Rawleigh C. Howe. Immunohistochemical Profiling of the Tumor Microenvironment in Ethiopian Breast Cancer Tissue: Insights into Pathology and Subtypes abstract. In: Proceedings of the 13th Annual Symposium on Global Cancer Research; 2025 Sep 16. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2025;34 (12Suppl): Abstract nr 9.