Xiaohong Rose Yang

Background:We previously identified three clinically relevant immune [i.e., low–tumor-infiltrating lymphocyte (TIL), high-TIL, and high–interferon-stimulated gene (ISG)] subtypes of luminal breast cancer using RNA sequencing in a cohort of women from Hong Kong. In this study, we evaluated whether standard, in situ immunohistochemistry (IHC), a more clinically accessible approach, could capture similar immune heterogeneity across intrinsic (PAM50) subtypes. Methods:In 148 patients with invasive breast cancer, we performed dual IHC staining for eight markers (CD3, CD8, CD20, FOXP3, CD68, CD163, PDL1, and IDO1) with pan-cytokeratin and quantified immune-positive cells in stromal regions by digital image analysis. Results:IHC marker expression strongly correlated with gene expression–based immune and intrinsic subtypes. Compared with luminal tumors classified as low-TIL, high-TIL tumors showed higher levels of CD3, CD8, CD20, PDL1, and IDO1. Similarly, high-ISG tumors expressed higher CD3, CD8, CD20, PDL1, and IDO1 than low-TIL tumors but were distinguished from high-TIL tumors by elevated CD163. Immune marker expression was generally higher in HER2-enriched and basal-like tumors than in luminal A and B tumors, though substantial variability existed within each subtype. Luminal B tumors expressed higher levels of CD3, CD8, CD20, and CD163 compared with luminal A tumors. Notably, immune infiltration was more strongly aligned with aggressive tumor features such as high grade, risk of recurrence scores, and TP53 mutations than with estrogen receptor/progesterone receptor expression. Conclusions:These findings confirm that subsets of luminal tumors harbor inflamed or macrophage-driven immune microenvironments. Impact:Parsimonious IHC panels can perform immune classification, supporting their potential utility in refining subtype stratification and informing clinical decision-making, particularly in resource-limited settings.

PAM50 subtype and immune marker expression among breast cancer patients participating in the Hong Kong Breast Cancer Study.

Distribution of immune markers by ESR1 quartiles among patients with Luminal B tumors in the Hong Kong Breast Cancer Study.

Association of Select Immune Marker Expression with ROR Score, Adjusted for PAM50 Subtype.

Relation of Estrogen-response pathway score with immune marker expression among breast cancer patients participating in the Hong Kong Breast Cancer Study.

Distribution of immune markers by ESR1 quartiles among patients with Luminal A tumors in the Hong Kong Breast Cancer Study.

Distribution of immune markers by ESR1 quartiles among patients with non-luminal tumors in the Hong Kong Breast Cancer Study.

Distribution of immune markers by PIK3CA mutation status among breast cancer patients participating in the Hong Kong Breast Cancer Study.

Relation of Risk of recurrence score with immune marker expression among breast cancer patients participating in the Hong Kong Breast Cancer Study.

Clinical ER/PR subtypes and immune marker expression among breast cancer patients participating in the Hong Kong Breast Cancer Study.