This is a study of drug KB004 in patients with recurrent glioblastoma (GBM). Eligible patients with measurable tumours will receive an initial trace (5mg) dose of zirconium labelled KB004 (89ZrKB004) on day 1 followed by sequential PET imaging over 1 week to determine its biodistribution into GBM and normal tissues. Safety assessments and pharmacokinetic (movement of drug) sampling will also be undertaken over this time. On Day 8, patients commence weekly KB004 infusions over 2 hours with standard premedications. Three cohorts are planned in this study (3.5mg/kg, 5.25 mg/kg, 7.9 mg/kg; additional dose levels may be explored based on toxicity, efficacy and biodistribution data as determined by the safety monitoring committee). On day 36, patients receive both 89ZrKB004 and KB004, allowing assessment of receptor occupancy to guide RPTD determination. Response rate (RANO) and survival data will be collected and patients benefiting may continue KB004 treatment until disease progression. Primary objective: to determine the toxicity and RPTD of KB004 in patients with advanced GBM.