Although p53 is clearly involved in the salvage pathway to DNA damage, its 
frequent mutations do not explain the efficacy of radiotherapy and chemotherapy. 
Indeed, around 50% of all human cancers show mutations in p53, and a further 
fraction show a functional inactivation of the protein. Nevertheless, patients 
seem to respond to therapy that would otherwise require a functional p53. At 
least in part, these responses could be explained by the pathway mediated by 
p73. This mechanism is parallel to, but independent of the p53 pathway. Several 
pieces of evidence show a significant interaction between these two proteins. 
Therefore, while p53 can be rightly defined as the guardian of the genome, we 
could think of p73 as the "assistant" guardian of the genome!