GFAP and glioblastoma: However, in 2014, three groups reported the successful isolation and characterisation of CTCs from the peripheral blood of patients with GBM.95–97 In a first study, glial fibrillary acidic protein-expressing CTCs were detected in 29/141 patients with GBM.95 These CTCs were identified in the density gradient purified mononuclear fraction of peripheral blood and further validation was based on the expression of EGFR mutations and aberrations that matched the primary GBM tumours.