To recapitulate the genetic complexity, variable mutational load, and frequent mutation of TP53 observed in human UPS and dedifferentiated/pleomorphic LPS [15], primary sarcomas were generated in wild-type 129/SvJae mice aged 6 to 10 weeks through the injection of adenovirus-expressing Cas9 endonuclease and sgRNA-targeting Trp53, followed by injection of 3-methylcholanthrene (MCA) into the gastrocnemius muscle (p53/MCA model). This evidence concerns the gene TP53 and undifferentiated pleomorphic sarcoma.