TP53 and cancer: The generation of p53 knockin alleles in mice provided direct in vivo evidence for the GOF activities of mutant p53. Knockin mouse models that express mutant p53R172H and p53R270H proteins, which mimic hot spot mutations that correspond to amino acids 175 and 273 in human cancers, respectively, develop tumors that exhibit a GOF phenotype in vivo, with high metastatic capacity compared to tumors in mice inheriting a p53-null allele (24, 25).