sarcoma treatment and prognosisretroperitoneal sarcoma prognosismetastatic sarcoma prognosisfibroid myxoid sarcomamyxoid sarcoma cancerpleomorphic sarcoma prognosismyxoid sarcoma pathology outlinesmyxoid liposarcoma prognosismyxoid spindle cell sarcomamyxoid liposarcoma treatmentmyxoid tumorsmyxoid liposarcoma metastasis