CD44 and glioblastoma: X-ray irradiation of U87MG GBM cells (137Cs τ-rays source, 2 Gy/day for 3 days) activates the expression of CD44 in these cells (37), and CD44 protein content was elevated in primary human GBM tumors that were developed in nude rat brain and undergone irradiation at a dose of 50 Gy, by 4 weeks after irradiation (38).