LAUSR

The importance of the immune microenvironment in triple negative and HER2‐amplified breast cancer (BC) is well‐established; less is known about the immune environment in luminal breast cancers. We aimed to assess for the impact of immune biomarkers on BC outcome in a group of luminal B patients with archived tissue and annotated clinical information. Patients with early breast cancer (EBC) treated in a single institution over a 14‐year period, with prospectively collected data were included. Luminal B EBC patients were identified and defined into three cohorts: A: grade 2 or 3, ER & PR positive, HER2‐negative; B: Any grade, ER positive, PR and HER2‐negative (Ki67 ≥ 14% in cohorts A & B); and C: Any grade, ER or PR positive, HER2‐positive. Within each cohort, patients with a relapsed BC event (R) were compared on a 1:1 basis with a control patient (C) who remained disease‐free, balanced for key characteristics in an effort to balance the contribution of each clinical group to outcome. Archival breast, involved and uninvolved axillary nodes were assessed by immunohistochemistry for biomarkers identifying effector and suppressor immune cells, and compared between R and C. In total, 120 patients were included (80, 22, and 18 patients in cohorts A, B, and C, respectively). R were 1.5 years older (p = 0.016), with all other characteristics being balanced. Overall, there were no statistically significant differences in immune biomarkers in breast or nodal tissue of R and C. However, there was a trend toward higher levels of TILs in breast tumors of C, while GAL‐9 was consistently expressed on lymphocytes and tumor cells in all breast and nodes of C and was absent from all tissues of R. These trends in checkpoint molecule expression deserve further research.