myxoid sarcoma prognosisfibroid myxoid sarcomamyxoid sarcoma cancermyxoid spindle cell sarcomamyxoid liposarcoma treatmentmyxoid tumorsmyxoid liposarcoma metastasismyxoid liposarcoma chemotherapyextraskeletal myxoid chondrosarcomamyxoid liposarcoma pathologymyxoid liposarcoma prognosismyxoid dermatofibrosarcoma protuberans