P2RX4 and cancer: The involvement of PKA in cancer has been extensively reviewed elsewhere.276,277 Another downstream effector, PLC, catalyses the production of diacyl glycerol (DAG) and InsP3 which both affect tumourigenesis.278 These secondary messengers play central roles in the signal transduction, linking purinergic signalling to other pathways especially those involved in embryonic and tumour development (i.e. Hippo, Wnt, Hedgehog, Notch and TGF-β).279–283 Genetic variations in the loci of purinergic receptors were demonstrated to have a prognostic value for tumour chemotherapy.