The comparable immunofluorescence staining on 2D-cultivated U87-MG cells and on the orthotopically grown U87-MG tumour along with the similarity of the KD values of the PET tracer (S)-(−)-[18F]fluspidine, indicate the conservation of sig1R expression and conformation over the translation from in vitro culture to in vivo implantation. This evidence concerns the gene SIGMAR1 and neoplasm.