metastatic myxoid liposarcomamyxoid liposarcoma histologymyxoid liposarcoma pathologymyxoid liposarcoma prognosismyxoid liposarcoma cancermyxoid spindle cell tumormyxoid liposarcoma pathology outlinesmyxoid sarcoma prognosismyxoid sarcoma cancermyxoid cellshurthle cell neoplasmspindle cell melanoma treatment