IGFBP4 and nasopharyngeal carcinoma: Interestingly, while the plasma level of IGFBP-1 from NPC patients was significantly higher than in healthy control volunteers (P = 0.034), no significant differences were observed between the plasma levels of the other IGF soluble receptor or binding proteins, including IGF-1SR, IGFBP-2, IGFBP-3, IGFBP-4 or IGFBP-6.