CALCA and glioblastoma: Comparative expression of 138 different GPCRs has revealed high levels of CALCRL mRNA, specifically in human glioblastoma cancer stem-like cells compared to significantly lower expression in human brain tumour U87MG cells, human astrocytes and foetal neural stem cells [31], although CALCRL is widely expressed in normal brain [21] as it functions as the predominant receptor for the neuropeptide CGRP.