The Tumor-Immune Microenvironment (Tme) In Hr+/Her2-Metastatic Breast Cancer (Mbc): Relationship To Non-Metastatic (Met) Tumors And Prior Treatment (Tx) Received.

1054Background: HR+/HER2- primary breast tumors demonstrate less anti-tumor immune activity than HER2+ or triple-negative BC. However, minimal data exist about the TME of HR+/HER2- met tumors, particularly in the tx-refractory setting. Prior analyses also have not looked at macrophages (macs), which may be important in HR+ BC. Methods: We obtained met tumor biopsies (bx) from HR+/HER2- mBC patients (pts) on a prospective tissue collection protocol. Tumor-infiltrating lymphocytes (TILs) were scored histologically, and cytokeratin, CD68, CD163, and PD-L1 on tumor cells (tPD-L1) were assessed by multiplex immunofluorescence (IF). Correlation between biomarkers and prior lines of tx was assessed by Spearman coefficient. A previously presented cohort of HR+/HER2- non-met tumors is included for comparison. Biomarker differences between non-mBC and mBC samples were assessed by Wilcoxon rank sum (TILs) and chi2 (tPD-L1) tests. Results: 33 HR+/HER2- mBC bx were analyzed from 30 pts (31 assessed for TILs, 21 by IF)...