Quantitative assessment of immune cell populations and associations with clinical outcomes in African-American (AA) versus Caucasian triple-negative breast cancer (TNBC).

Abstract

e14180 Background: Tumor infiltrating lymphocytes (TILs) are powerful prognostic and predictive factors in TNBC. We hypothesized that survival differences in TNBC by race may be caused by differences in the tumor immune microenvironment. We assessed racial differences in the extent and composition of immune infiltration in TNBC and correlated these differences with clinical characteristics and disease-free survival (DFS). Methods: Formalin fixed paraffin embedded TNBC samples and clinical information were collected for n = 43 AA and n = 43 Caucasian cases, matched by diagnosis date and stage. Stromal TILs were assessed on H&E-stained slides. Multiplexed immunofluorescence was performed to quantify CD68 (macrophage), CD8 (cytotoxic T cell) and PD-L1 protein expression in the whole-section, tumor and stromal compartments. Average expression for each marker was calculated over all fields of view. Cox proportional hazards were used to assess associations between DFS, staining markers and clinical variables. Results: Characteristics of AA and Caucasian cases were not significantly different. There were 14 and 8 recurrences in the AA and Caucasian cohorts, respectively (median follow-up 8.7 vs 9.4 yrs). TIL counts (p = 0.031) and overall CD68 expression (p = 0.005) were higher in AA compared to Caucasian patients. 21% percent of AA cases had TIL predominant phenotype versus 3% of Caucasians, but CD8 expression was similar by race. PD-L1 expression was higher in stroma compared to tumor across all patients (median 401 vs 267 au, p = 0.002) and did not differ by race. Higher overall and stromal PD-L1 expression were associated with better DFS in the entire population (median 3501 vs 1895 days, p = 0.0009) and in each race separately. Higher CD68 expression was also associated with better DFS (median 3015 vs 2111 days, p = 0.0004). In multivariate analysis of DFS, stage at presentation remained significant (p = 0.002) in addition to PD-L1 and CD68 expression. Conclusions: AA TNBC had higher TIL counts and CD68 expression but similar CD8 and PD-L1 expression compared to Caucasians. High CD68 and PD-L1 expression were associated with better DFS in both race cohorts.