Immunohistochemical profiling of the tumor microenvironment in Ethiopian breast cancer tissue: insights into pathology and subtypes

Breast cancer (BC) is the most common malignancy globally and poses a significant public health challenge in sub-Saharan Africa (SSA). To date, the clinical use of immunotherapies has improved patients’ outcomes in high-income countries, but is not feasible in most countries in SSA. This study aimed to analyze the tumor microenvironment (TME) in Ethiopian BC samples to evaluate the immunogenicity of those tumors. Formalin-fixed paraffin-embedded (FFPE) tissue blocks ( n = 81) were collected to analyze tumor-infiltrating lymphocytes (TILs), tumor-associated macrophages (TAMs), and Programmed Death Ligand 1 (PD-L1) in BC. Immunohistochemistry (IHC) staining was performed to evaluate the expression of these biomarkers. Statistical analysis was conducted using R version 4.4.2. The non-luminal BC subtypes (triple-negative and HER-2 positive) demonstrated a significantly higher proportion of stromal CD20 + TILs ( p = 0.023), intratumoral CD3 + TILs ( p = 0.0075), and CD68 + TAMs ( p = 0.037) than the luminal subtypes. Moreover, stromal PD-L1 + expression ( p = 0.024), intratumoral PD-L1 + expression ( p = 0.025), intratumoral CD3 + TILs ( p = 0.023), and intratumoral CD163 + TAMs ( p = 0.015) were significantly higher in grade III BC compared to grades I and II. Infiltrating immune cells were more common in hormone receptor-negative and higher-grade BC, consistent with previous results in resource-rich countries.