2MO Expression levels of immune checkpoint markers (IC) in hormone receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancer (BC)

IC markers against which inhibitors are currently used/evaluated clinically, have not yet been studied in detail metastases (M) from patients with primary HR+/HER2- BC. In this study, we examined expression levels of these multiple M and tumors (P) BC who enrolled our postmortem tissue donation program UPTIDER (NCT04531696). 326 samples (23 untreated P 290 samples) 10 underwent bulk RNA sequencing (Lexogen). Quality control (QC) was set for 500000 assigned reads gene counts were normalized using variance stabilizing transformation. We selected being clinically investigated (BTLA, CD40, CD47, CD86, CD137, CD137L, CD158A, CD226, CTLA4, ICOS, LAG3, OX40, PD-1, PD-L1, TIM3, TIGIT) literature clinicaltrials.gov. Available matched FFPE evaluated histology (invasive lobular, ILC, no special type, NST) ER-status. Associations between sample status (outcome: vs P/ ER+ ER- M) individual assessed by logistic linear regressions data clustering patient the generalized estimating equation method. association specific interval (ssPMI) repeated sampling (at 1.5h intervals) same 7 patients. 324/326 passed QC (289 22 P) stable increasing ssPMI. TIM3was highly expressed, PD-1 among least expressed M. Intra-patient inter-M heterogeneity observed all markers. showed lower OX40 TIGIT (Odds ratio (OR) range: 0.27-0.53, p<0.05) higher TIM3 BTLA (OR range:1.37-6.19, compared to P. BTLA, more NST ILC 1-1.43). CD40 found both NST: 1.02-1.37, OR ILC: 1.12-5.52). This study sheds light on as well impact ER-expression.