Thus, SDF-1-CXCR4 axis-mediated homing of tumor cells to the BM is commonly observed in various hematopoietic malignancies [30] and carcinomas including HNSCC [6,31,32], whereas inhibition of CXCR4 blocks this homing [7]. Here, CXCL12 is linked to head and neck squamous cell carcinoma.