The A-172 cell line is not generally regarded as a good model for GBM (cultured with serum and non-tumorigenic), and as we had originally made the observation that CTR is upregulated in primary tumours including glioma stem cells,25 we sought to confirm our results in the primary high-grade glioma line GBM-L2 (Figures 1f–j) that are representative of glioma stem cells38,39 and are grown serum-free. Here, CALCR is linked to central nervous system cancer.