Tumor Infiltrating Lymphocytes Associated With Brain Metastasis In Breast Cancer.

2059 Background: Breast cancer represents the second most common cause of brain metastasis (BM). Though tumor-infiltrating lymphocytes (TILs) and immunotherapies have been studied in primary breast cancer, little is known about TILs in BM from breast cancer. The aim of this study is to characterize the immune response to BM in breast cancer. Methods: The cohort included 75 initial and recurrent BM samples and 20 matched primary breast tumors. Stromal (sTILs) were evaluated on Hu0026E sections and scored according to international TILs working group guidelines and categorized as having no, low (1-5%), moderate (6-20%) or high ( u003e 20%) TILs. Tumor DNA/RNA was extracted on corresponding archival FFPE material. Gene expression profiling was performed using Affymetrix Human Transcriptome Array 2.0 microarrays. PAM50 subtypes were assigned by clustering samples using median-subtracted PAM50 gene expression levels. Gene expression levels of programmed cell death 1 (PD1), programmed cell death ligand 1 (PD-L1), cytot...