Radiotherapy in combination with surgery and chemotherapy is the most commonly prescribed treatment for GBM, but the prognosis of patients with GBM remains poor due to therapeutic resistance and tumor recurrence.1,28 Here, we show that the radiation-induced increase in Rab27b-EREG signaling contributes to radioresistance in GBM cells and further exerts pro-proliferative paracrine effects on surrounding cells. Here, EREG is linked to glioblastoma.