TP53 and osteosarcoma: In a mouse model of Li-Fraumeni syndrome, an increased incidence of metastatic osteosarcomas was found in heterozygous mice with an endogenous mutant allele of TP53 (corresponding to the R127H mutation).34 In comparison to parental MG63 cells, MG63 cells with ectopic expression of a TP53 mutant (R248W/P72R) exhibited enhanced sphere formation and clonogenic growth, indicating that this GOF could be the root cause of the dedifferentiation of MG63 cells into cancer stem cells.35 We found abnormal accumulation of the TP53 protein in HOS and 143B cells compared with U2OS and MG63 cells.