Glioblastomas (GBM) are rare tumors of poor prognosis and their treatment is based on surgery followed by radiochemotherapy. Clinical and imaging evaluation is not always straightforward: the more or less complete surgery, the pseudo-progression after radiochemotherapy, the radionecrosis, the diagnosis of the relapse and the follow-up under anti-angiogenic can pose problems Clinicians and radiologists. Accessibility to a plasma tumor molecular marker would greatly facilitate the follow-up of these patients.