CDKN1A and glioblastoma: While we previously documented this increased response in 80S4 cells (wtTP53 p21-/-), increased sensitivity of other three cell lines; 19S186 cells (mutTP53 p21-/-); SW1222 cells (mutATM) and U251 cells (glio) was unexpected, especially U251 which is a very resistant glioblastoma cell line based on in vitro radiosensitivity.