DKK1 and glioblastoma: Following normalization and statistical analysis of fluorescence intensity data by t test, we identified that the difference of DKK-1 protein expression was significant between the culture medium and cell lysate in 12 glioblastoma cell lines (p < 0.05), consistent with the fact that DKK-1 was a secreted peptide shown previously to influence cell growth, differentiation and apoptosis by inhibiting Wnt signaling [18].