To confirm whether CXCR7 overexpression induces the migration and invasion of HNSCC cells by modulation of TGF-β1/Smad2/3 signaling, we knocked down CXCR7 expression using siRNA in CXCR7-overexpressed cells (Fig. 4A). The gene discussed is SMAD2; the disease is head and neck squamous cell carcinoma.