CCR7 expression and spatial distribution in inflammatory breast cancer: A baseline characterization for therapeutic targeting

Purpose: Inflammatory breast cancer (IBC) is a rare, highly aggressive subtype marked by rapid proliferation, extensive angio-/lymphangiogenesis, and early metastasis. CCR7, a chemokine receptor involved in immune trafficking, promotes tumor migration toward lymphatics via CCL19/CCL21. This study provides an integrated genomic, protein, spatial, and functional evaluation of CCR7 in IBC to assess its therapeutic potential. Methods: Clinical analysis used genomic data from HR+ HER2- and TNBC IBC compared with subtype-matched non-IBC. CCR7 expression was assessed in IBC and non-IBC cell lines by immunoblotting; ligand secretion (CCL19/CCL21) in tumor and stromal cells was measured by ELISA. CCR7 localization was evaluated using subcellular fractionation and IF, along with testing of a CCR7-blocking antibody. Multiplex IF was performed on BCM PDX models representing distinct CCR7 genomic and protein states. Functional studies included the CCR7 antagonist Navarixin, CCL19/21-induced migration assays, and generation of CCR7 CRISPR knockout clones. Results: CCR7 CNAs occurred in both IBC and non-IBC but did not correlate with mRNA or protein levels. CCR7 protein was broadly expressed, with strongest membranous expression in A3250 and variable levels in IBC-3, SUM-190, and SUM-149. The blocking antibody reduced membranous CCR7 only in A3250, indicating subtype-specific accessibility. IBC cell lines did not secrete CCL19/CCL21, supporting reliance on stromal ligands, which varied by coculture. Across six BCM PDXs, CCR7 was consistently expressed, whereas ligand levels were heterogeneous; MBI-117 showed high CCL19/CCL21. Spatial profiling revealed CCR7⁺ tumor cells aligned along Podoplanin⁺ lymphatics with CCL21⁺ stromal cells and CD163⁺ macrophages enriched around CCR7⁺ emboli. Navarixin reduced proliferation in IBC3 and SUM-190 by 96h, and CCL19/21 enhanced migration in A3250 and SUM-149. CCR7-KO SUM-149 clones were generated, with functional analyses ongoing. Conclusion: CCR7 expression in IBC is independent of copy number and supported by a ligand-rich microenvironment that positions CCR7⁺ tumor cells along lymphatics. Integrated genomic, spatial, and functional data support CCR7 as a therapeutic target in IBC, with studies ongoing.