Although the levels of CXCR4 expression correlate directly and strikingly with the degree of metastasis in NPC [19] and in several human carcinomas [13], [42], [43], [44], the functional role of tyrosine sulfation of CXCR4 in these tumors is largely unknown. The gene discussed is CXCR4; the disease is nasopharyngeal carcinoma.