AR and glioma: Extracellular purines have been implicated in several aspects of GBM biology, such as proliferation,26 migration,27 invasion28 and death.29 The concentration of adenosine in the extracellular fluid of glioma tissue was reported to be in the low micromolar range,30 which is sufficiently high to stimulate all the four of the adenosine receptor (AR) subtypes (A1, A2A, A2B and A3).31 Each of the ARs have a pivotal role in the control of tumour growth and invasiveness32, 33, 34 but to date, no data on their role in CSC biology are available.