MMP9 and neoplasm: However, a deficiency of endogenous IFN‐β may allow neutrophils to express higher levels of C‐X‐C chemokine receptor type 4 (CXCR4), vascular endothelial growth factor (VEGF), and matrix metalloproteinase 9 (MMP9), thus promoting angiogenesis, mobility, and tumor homing.