GPR55 and central nervous system cancer: The ECS comprises prototype neuroactive molecules (anandamide), cannabinoid-type receptors (CB1, CB2, GPR55) and enzymes (FAAH1 and monoacyl-glycerol lipase (MAGL)) and there is a tight link to a wide range of cancers, including, but not limited to, those of lung, glioma, pancreas, oral and embryonal origin [35,36,37].