Prospective evaluation of serum glial fibrillary acidic protein (GFAP) as a diagnostic marker for glioblastoma

Glioblastoma (GBM) is the most common malignant primary brain tumor. Although clinical presentation and brain imaging might be suggestive, histopathological evaluation by means of a brain biopsy is routinely performed to establish the diagnosis. A serum marker indicative of GBM may simplify the diagnostic work-up of patients suspected to having a brain tumor. We prospectively examined 113 patients with newly diagnosed single supratentorial or infratentorial space-occupying brain lesions. Glial fibrillary acidic protein (GFAP) levels were determined from venous blood samples via a prototype ELISA assay prior to any invasive procedures. Serum levels of GFAP were correlated with histopathological findings and MRI parameters. GFAP values were significantly higher in GBM patients (n = 33) compared to all other tumors (p < 0.001). A GFAP serum concentration of ≥0.01 µg/L revealed a sensitivity of 85 % and a specificity of 70 % for differentiating GBM from other entities. By applying a GFAP cut-off point of 0.20 µg/L, specificity was maximized (99 %), but sensitivity dropped to 27 %. In GBM patients, serum GFAP values were significantly correlated with tumor volume. GBM patients with high GFAP levels showed more in vivo GFAP expression as well as more necrosis and perilesional edema compared to GBM patients having low or non-detectable GFAP levels. GFAP serum concentrations differentiated between patients with GBM and patients with cerebral mass lesions of other entities with a moderate diagnostic accuracy. Serum GFAP levels in GBM patients were positively correlated with tumor volume and histopathological tumor characteristics.