NANOG and glioblastoma: In contrast, the median of OCT-4 expression was 0.47 in secondary GBM and 2.03 in primary GBM; the median of NANOG expression level in secondary GBM was 0.13 while 0.35 in primary GBM, and the median of CD133 expression level was 1.28 for secondary GBM and 2.26 for primary GBM.