ESM1 and glioblastoma: ELISA analysis demonstrated that Endocan, the ESM1 gene product, was secreted by HBEC-5i and glioblastoma patient-derived VE cells (TEC 14 and TEC15) at concentrations exceeding 100 pg/ml, while conditioned media (CM) from normal human astrocytes and gliomasphere lines (1079, 157, 711, and 1051) contained nearly undetectable amounts of Endocan (Fig. 1d).