TGFB1 and glioblastoma: In comparison with parental GBM cells, the secretion of TGF-β (25.7 ± 2.69 pg/mL vs. 1607.7 ± 19.16 pg/mL vs.1207.0 ± 27.33 pg/mL for 1306MG, 3.5GR6, and R6T3; 995.4 ± 10.98 pg/mL vs. 1234.1 ± 23.10 pg/mL vs. 1058.1 ± 8.56 pg/mL for U87MG, 2GR4, and R4T3) increased in both RR and RTR (Figure 1A).