By densitometry analysis, we distinguished three ranges of BCL-xL expression in GBM tumorspheres compared to differentiated cells: high BCL-xL expression (U-87 MG and SC2), moderate BCL-xL increase in expression (N14-0510, N14-1525 and SF 767) and lastly, a group of GBM cells displaying no up-regulation of BCL-xL levels in tumorspheres compared to differentiated cells (N13-1520, A-172, 5706 and U-251 MG). The gene discussed is BCL2L1; the disease is glioblastoma.