FN1 and glioblastoma: As fibrillar proteins like laminins, collagen IV and fibronectin are found almost entirely along the basement membrane of vessels,[31, 32, 33] we initially co‐stained glioblastoma samples with a fibronectin polyclonal antibody, which identifies all fibronectin isoforms, irrespective of their tension, and COL4A1 to localize fibronectin with respect to collagen IV.