Prognostic Significance of CD8 T-cell Spatial Biomarkers in ER+ and ER- Breast Cancer

Tumor Infiltrating Lymphocytes (TILs) have been shown to be prognostic in Triple-Negative Breast Cancer (TNBC), but are rarely considered in other subtypes, particularly estrogen receptor (ER) positive cancers (70-80% of breast cancers), due to lower TIL counts. However, the spatial proximity of lower abundance TILs has not been evaluated in relation to breast cancer prognosis. In this study, multiplex immunofluorescent-stained images were used to identify cell types based on cytokeratin (Ck), CD8, and FoxP3 expression. Using distance-based visual morphometry between epithelial and immune cells, we computed new metrics, proximity and consistency, which capture spatial relationships between Ck+ tumor cells and CD8+ T-cells. Prognostic significance of proximity and consistency were compared to lymphocyte counts using log-rank tests. Worse relapse-free survival (RFS) was observed for both ER+ and ER-breast cancers with low proximity and consistency of CD8+ cells. Among ER negative breast cancers, proximity had the highest RFS hazard ratio (HR 1.84, 95% CI [1.18,2.87]). Among ER positive participants, RFS hazard ratios for proximity and consistency were 2.04 (95% CI [1.39, 2.98]) and 1.82 (95% CI [1.23, 2.69]) respectively. These associations were stronger than those observed for lymphocyte count (HR 1.35, 95% CI [0.92,1.98], log-rank p-value = 0.13). These IF-derived spatial metrics were also associated with established TILs metrics and RNA-based expression-based measures of tumor adaptive immune response. The prognostic significance of proximity in ER+ breast cancer implies that spatial parameters may identify individuals who would benefit from immune therapy; up to 75% of breast cancers experience T-cell proximity suggestive of immune susceptibility.