1141 Spatial immune profiling across the lobular breast cancer continuum reveals progressive immune exclusion from precursor lesion to invasive disease
Year: 2026
Type: conference-abstract
Abstract: Background Invasive lobular carcinoma (ILC) is the second most common breast cancer (~15% of cases) yet its tumor immune microenvironment (TME) remains poorly characterized. ILC has been shown to have increased immune infiltrate as compared to invasive ductal carcinomas yet immune checkpoint therapy has not been tested in ILC. Lobular carcinoma in situ (LCIS) is an established ILC precursor, therefor evaluating the spatial immune environment from normal breast to LCIS to ILC provides an opportunity to map immune architecture across disease progression.Methods Multiplexed immunofluorescence (mIF) was performed on 48 formalin-fixed paraffin-embedded (FFPE) samples spanning normal breast (n = 9), LCIS (n = 21), and ILC (n = 18). A 24-plex panel targeting T cell subsets (CD4, CD8), B cells (CD20), natural killer (NK) cells (CD56, CD16), macrophages (CD68, CD163), dendritic cells (DC)(CD11c), and functional markers (LAG-3, TIM-3, FoxP3, PD-1, PD-L1, Ki-67, Granzyme-B) was used. Spatial analyses included compartment-specific tumor-infiltrating lymphocyte (TIL) scoring with double normalization correcting for both tissue area and cellularity, permutation-based CD8 exclusion index scoring, and tissue archetype discovery via UMAP and K-means clustering. Immune phenotype was classified per International TIL Working Group (ITWG) criteria as immune excluded, inflamed, or desert.Results ILC displayed near-universal immune exclusion: 94.4% excluded and 5.6% inflamed, compared to 66.7% excluded in LCIS and 22.2% excluded in normal breast. Double-normalized CD8 stromal TIL density was significantly elevated in ILC stroma relative to LCIS and normal tissue, whereas intratumoral CD8 density was markedly reduced, yielding a median CD8 exclusion index of 0.91 in ILC versus 0.51 in LCIS and 0.41 in normal tissue (FDR < 0.05 for all TIL metrics). Spatial archetype analysis identified 8 tissue organization patterns, with 7 showing significant condition-specific enrichment (FDR < 0.05). ILC was enriched for endothelial and epithelial-dominant configurations (A4, A7) and virtually depleted of archetypes prevalent in normal tissue (A3, A5), reflecting the distinct spatial reorganization of the lobular tumor microenvironment. Stratification by HER2 status revealed that HER2-negative tumors had significantly higher CD8 exclusion (median exclusion index 0.89 vs. 0.62 in HER2-positive, p = 0.036), while HER2-positive cases were more likely to show an inflamed phenotype (25% vs. 13%), suggesting HER2 status modifies the spatial immune architecture.Conclusions Immune exclusion is the dominant TME phenotype in ILC, with CD8 T cells spatially restricted to stroma and progressively excluded from tumor epithelium as disease advances. HER2-negative lobular tumors exhibit the most pronounced exclusion phenotype despite comparable immune cell abundance, with implications for patient selection in immune checkpoint inhibitor therapy.
Institution: Providence Portland Medical Center
Language: English
Subfield: Oncology
Field: Medicine
Domain: Health Sciences
Open Access status: gold
Estimated APC paid: $2,490
OpenAlex ID: W7225153122