To determine the activity of the p53 pathway, all cell lines were subjected to radiation-induced DNA damage, and the induction of two major targets downstream of p53 was determined – CDKN1A (p21) and BAX. The cell line U-2 OS, which is a human osteosarcoma cell line expressing wild-type p53 and RB1, but lacking p16 [28, 29], was used as the control. This evidence concerns the gene RB1 and osteosarcoma.