Knockdown of SPINK6 inhibited migration, invasion, and metastasis of highly metastatic nasopharyngeal carcinoma cells. A, SPINK6 expression in stable SPINK6 knockdown cells is shown. Top, mRNA level; bottom, protein level in condition medium with relative gradation shown below the band. B, Knockdown of SPINK6 suppressed migration and invasion of S18 and 5–8F cells. C, Statistical results from B. Column, mean; bar, SEM (from triplicates). **, P < 0.01 by Student t test. D, Knockdown of SPINK6 decreased in vivo metastatic rate of S18 and 5–8F cells. Cells (1× 105) were subcutaneously injected into the left hind footpad of nude mice, and metastasis to the left popliteal LN was measured. P value, result of χ2 test. E, Knockdown of SPINK6 impaired in vivo liver metastasis of S18 cells. P value, result of Student t test. F, Representative picture from E. Top, representative picture of livers; scale bar, 1 cm; bottom, representative H&E staining of livers; scale bar, 100 μm. NC, negative control, with detail shown in Supplementary Table S2.