Abstract 4050: Molecular characterization of residual triple-negative breast cancers after neoadjuvant chemotherapy identifies immune composition and features associated with clinical outcome

Abstract

Abstract Although neoadjuvant chemotherapy (NAC) induces complete response in 30-40% of triple-negative breast cancers (TNBC), patients with residual disease at surgery have poor prognosis and limited treatment options until recurrence. Tumor-infiltrating lymphocytes (TILs) in the residual disease are a positive prognostic factor, but the composition of TILs has not been explored in granularity, and how specific immune composition of the tumor guides outcome is unclear, resulting in a lack of understanding of how to employ immunotherapies in the adjuvant setting. We assessed multiple immunologic biomarkers in a series of 100 residual TNBCs after NAC. Immune markers were assessed by multiple methods, including H&E TILs analysis, standard immunohistochemistry (IHC; HLA-A, CD4, CD8, LAG-3) and multiplexed immunofluorescence (mIF; HLA-DR, GZMB, CD4, CD8, PD-L1, pan-CK). TILs and IHC were scored by clinical research pathologists and IF was scored by AQUA® analysis. Where multiple markers were multiplexed together, subset analyses was performed. Association among parameters were assessed (n=83) including clinical outcome after surgery (n=79). As previously demonstrated, TILs in residual tumors after NAC predicted both RFS and OS. H&E-scored TILs were correlated to both CD4 and CD8 as scored by IHC or IF (Pearson’s r range 0.41-0.55; all p<0.001). CD4 and CD8 measured by IHC and IF were highly correlated (r=0.68 and 0.71, respectively; p<0.0001). CD4 and CD8 were also highly correlated to one another (r=0.67; p<0.0001). Likewise, infiltration by CD4 or CD8 were each associated with improved recurrence-free (RFS; coxPH p=0.004 and 0.007, respectively) and overall survival (OS; p=0.003 and p=0.005, respectively). Tumor and stromal PD-L1 (E1L3N) staining was associated with marginally poorer RFS (p=0.06) but not OS (p=0.94). Colocalizing GZMB and CD8 cells by mIF yielded a paradoxical finding that cytotoxic CD8 cells were associated with significantly worse RFS and OS (p=0.004 and 0.0004, respectively). In a multivariate model, total PD-L1, total CD4, and GZMB+CD8+ T cell infiltration each remained significant, suggesting independence, and provided a strongly predictive signature for RFS (p=4.6e-06). In the same analysis to predict OS, only GZMB+CD8+ T cells remained significant (p=0.0002). High GZMB+ CD8+ T cells were not associated with PD-L1 expression, but were associated with low LAG-3 expression (p=0.0009). Although the results of this study remain to be validated in larger cohorts, the paradoxical finding that GZMB+ CD8+ T cells are a negative prognostic factor for long term outcome in NAC-treated TNBC is an intriguing result. We hypothesize it may be these patients whose T cells are poised for cytotoxic activity but remain restricted through high PD-1 expression, and thus may benefit from adjuvant immunotherapy. Citation Format: Caroline Nebhan, Paula I. Gonzalez-Ericsson, Roberto Salgado, Jennifer Bordeaux, Ju Young Kim, Christine Vaupel, Henry Gomez, Justin Micah Balko. Molecular characterization of residual triple-negative breast cancers after neoadjuvant chemotherapy identifies immune composition and features associated with clinical outcome [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4050.