IGFBP6 and nasopharyngeal carcinoma: The plasma level of eight members of the IGF system, including IGF ligands (IGF-1 and IGF-2), IGF-1 soluble receptor (IGF-1 sR), and IGF binding protein (IGFBP-1, IGFBP-2, IGFBP-3, IGFBP-4, and IGFBP-6) were detected in healthy controls and patients with NPC (n = 10, respectively) using a Human Cytokine Antibody Array (Fig. 1).