Here, we demonstrate the expression of MOR in commonly used GBM cell lines (U87, U251, U373) and primary GBM cells isolated from a patient biopsy by Western blotting (Fig. 1a) and immunocytochemistry (Fig. 1b), confirming and extending the finding that MOR is expressed in a wide range of GBM cells to a similar extent. Here, OPRM1 is linked to glioblastoma.