Spatial remodeling of the tumor-immune microenvironment (TIME) on neoadjuvant chemo-immunotherapy (NCIT) in patients (pts) with hormone receptor positive (HR+) early breast cancer (eBC) by multiplex immunofluorescence (mIF).

e12645 Background: NCIT efficacy remains limited in HR+ eBC. Given the role of cell interactions in antitumor immunity, we evaluated TIME spatial dynamics in this subtype. Methods: This is an exploratory analysis from trial NCT02999477 randomizing pts to a monotherapy run-in (A: nab-paclitaxel; B: pembrolizumab) followed by both in combination (NCIT). Biopsies were obtained at baseline (BL), after run-in (week 3, W3), and on NCIT (W7). At each timepoint, 4 tissue sections were stained with 4 mIF panels: T-cell (CD4, CD8a, FOXP3), activated T-cell (CD8a, granzyme B, Ki67), antigen presenting cells (APCs) (HLA-ABC, HLA-DR, CD8a), and myeloid (CD68, CD206, HLA-DR), all with pan-CK and nuclear staining. Objectives were to characterize immune cell densities (cell/mm2), changes from BL, tumor–immune nearest-neighbor distance (μm), and explore associations with clinicopathological features, residual cancer burden (RCB) (0/I vs II/III, Kruskal–Wallis) and event-free survival (EFS) (Cox model) (p 50), race (White vs non-White), stage (II vs III). At BL, RCB-0/I pts had numerically higher density of helper T cells (Th) (CD4+; median 2154.1 vs 890.0; p = .06), cytotoxic T cells (Tc) (CD8+; 728.1 vs 367.9; p = .08), activated Tc (6.1 vs 1.3; p = .06), APCs (HLA-ABC+, HLA-DR+: 124.6 vs 51.3; p = .36), and macrophages (CD68+CD206+; 63.4 vs 26.7; p = .25) vs RCB-II/III. On treatment, RCB-0/I pts had numerically greater % increase in cell density at W3 from BL than RCB-II/III for Tc (median 52.7 vs −62.0; p = .64), activated Tc (269.5 vs −83.6; p = .13), APCs (417.6 vs 24.9; p = .60), and macrophages (780.2 vs −61.4; p = .24). At W7, APCs continued to show greater % increase in RCB-0/I vs RCB-II/III (1583.3 vs 121.3; p = .38). At BL, distance from tumor area was numerically shorter in RCB-0/I vs RCB-II/III for Tc (median 55.2 vs 79.3; p = .20), activated Tc (1015.4 vs 2274.1; p = .39), APCs (216.4 vs 370.4; p = .39), and macrophages (276.4 vs 517.8; p = .50). On treatment (W3, W7), % changes from BL in tumor-immune distance were heterogeneous in RCB-0/I vs RCB-II/III across most immune cells. At W3, APCs (−52.2 vs 27.6; p = .24) and macrophages (−37.7 vs 20.2; p = .18) got numerically closer to tumor vs BL in RCB-0/I. At BL, pts with RCB-0/I had a numerically shorter distance between HLA-ABC+ cells and CD8+ cells vs RCB-II/III (median 20.5 vs 30.8; p = .36). A continued numerical % decrease from BL was seen at W3 (−57.1 vs 5.3; p = .12) and W7 (−65.2 vs −16.5; p = .38). No density or distance thresholds predicted EFS. Conclusions: TIME remodeling was heterogeneous, trending toward greater Tc and APC density and proximity to the tumor area in RCB 0/I. Clinical trial information: NCT02999477 .