AR subtypes have different affinities to adenosine; A1 and A2A are high affinity receptors and A2B and A3 are low affinity receptors; therefore, in pathological conditions, such as cancer, extracellular adenosine levels are increased and mainly activate A2BAR and A3AR subtypes enhancing several signaling pathways, such as PI3K/AKT, MAPK, among others [27,29,33]. Here, AR is linked to cancer.