SIGMAR1 and central nervous system cancer: As the microenvironment is known to influence gene expression, e.g., the hypoxia-stimulated HIF-1α expression in glioma or the culture mode (2D vs. 3D)-dependent differential gene expression of colorectal cell lines [58,59,60,61], we further investigated the expression of sig1R in the intracerebral U87-MG tumour.