Fig 5. Trp53^fl/flPten^fl/fl mice injected with Ad CMV-Cre form undifferentiated pleomorphic sarcoma.

A) Histology and immunophenotype of UPS arising after SQ injection of Ad CMV-Cre. H&E section reveals a proliferation of markedly atypical spindle cells with numerous mitotic figures (arrows) as well as tumor necrosis (*). No line of differentiation was identified by the neoplasm’s light microscopic appearance or immunohistochemical profile, supporting classification as UPS. B) Histology and immunophenotype of typical UPS arising in skeletal muscle. The histological appearance and immunophenotype is similar to the subcutaneous UPS present in (A). SMA is variably positive in different examples, similar to human UPS. The asterisk highlights skeletal muscle fibers in the H&E section as well as the desmin stain, where they serve as an internal control. C) Histology and immunophenotype of PRMS. H&E section reveals a proliferation of markedly atypical spindle cells admixed with rounded rhabdomyoblasts (arrow). Skeletal muscle differentiation is confirmed by the identification of various foci expressing myogenin and desmin. D) Phospho-AKT was variably present. In some sarcomas, such as the PRMS tumor and some of the UPS tumors, phospho-AKT could be identified more diffusely (left panel). In other UPS tumors, it was more focal (right panel).