IGFBP6 Expression Correlates with Macrophage Presence in Triple- Negative Breast Cancer Tumors

Introduction: Insulin-like growth factor 2 (IGF2) is a key factor in communication between cancer-associated fibroblasts (CAFs), tumor-associated macrophages (TAMs), and cancer cells, enhancing cancer cell survival. CAFs produce IGF2, which activates signaling pathways in cancer cells and has immunosuppressive effects. IGF-binding protein 6 (IGFBP6) is a specific IGF2 inhibitor that affects tumor behavior. Previous findings linked low IGFBP6 expression in triple‑negative breast cancer (TNBC) cells to increased metastatic potential. Method: Single-cell RNA-seq and mRNA bulk sequencing of tumors from the Cancer Genome Atlas portal were analyzed. Results: CAFs were the primary IGF2-producing population, accounting for 66.5% of IGF2-positive tumor cells. IGFBP6-positive cells were distributed between CAFs (48%) and cancer cells (30%). IGF2 was mainly expressed in CAFs and vascular cells; IGFBP6 was expressed in a broader range of cells. A negative correlation between IGFBP6 expression and macro-phage proportion was observed in breast cancer samples. Higher macrophage content in tumors was found to be associated with earlier disease recurrence. Discussion: The findings supported a stromal‑led paracrine circuit in which CAF–derived IGF2 was locally buffered by IGFBP6 6 from stromal and cancer compartments, reducing free ligand and macrophage accumulation. This axis offers mechanistic insight into immune re-modeling and may explain links between low IGFBP6, increased macrophages, and earlier recurrence. Conclusion: CAFs are the principal source of IGF2 in TNBC, and higher IGFBP6 expression associates with fewer tumor macrophages and delayed recurrence, highlighting the CAF–IGF2–IGFBP6–macrophage pathway as a potential biomarker and therapeutic target.