Integrative In Silico and FFPE Tissue Analyses Elucidate Upregulated Genes in Colorectal Cancer Enriched for Tie2-Expressing Macrophages/Monocytes

Tumor-associated Tie2-expressing monocytes/macrophages (TEMs) have been implicated in promoting angiogenesis and metastasis in colorectal cancer (CRC), yet the molecular mechanisms linking TEMs infiltration to tumor metastasis and progression remain incompletely defined. This study investigated the distribution of TEMs in CRC and their association with gene expression profiles, microvessel density (MVD), and clinical outcomes. Immunohistochemistry on 30 formalin-fixed paraffin-embedded (FFPE) primary CRC samples revealed that TEMs, which characteristically express tyrosine kinase with immunoglobulin and epidermal growth factor homology domains 2 (Tie2) receptor and CD14, preferentially localize to perivascular regions and are associated with higher histological grade, tumor size, lymph node metastasis, and increased MVD. However, Tie2⁻/CD14⁺ macrophages and CD68⁺ tumor-associated macrophages (TAMs) showed uniform stromal distribution. Gene set enrichment analysis (GSEA) of in silico transcriptomic datasets of metastatic CRC (mCRC) identified enrichment of pathways related to cell–cell recognition, calcium signaling, transcription regulation, and metalloexopeptidase activity in Tie2⁺/CD14⁺ tumors. Subsequent qRT-PCR validation on FFPE primary CRC samples confirmed significant upregulation of C-C chemokine receptor 7 (CCR7), platelet-derived growth factor A (PDGFRA), CBP/p300-interacting transactivator with glutamic acid/aspartic acid-rich carboxyl-terminal domain 2 (CITED2), and carboxypeptidase E (CPE) in TEMs⁺ regions. Notably, angiopoietin1 (Ang1), but not angiopoietin2 (Ang2), was significantly elevated in TEMs⁺ primary tumors. Kaplan–Meier analysis on 1336 CRC patients indicated that high expression of CITED2, CPE, and Ang2 is associated with reduced overall survival. Collectively, these findings suggest that TEM infiltration is linked to transcriptional regulation, biological processes, and enzymatic programs in CRC, potentially contributing to tumor progression and poor prognosis, and highlight CCR7, PDGFRA, CITED2, CPE, and Ang1 as candidate biomarkers for further mechanistic exploration.