American Urological Association - Dedifferentiated Liposarcoma
- Characterized by the coexistence of well-differentiated and poorly differentiated nonlipogenic areas, either within the same tumor or between a primary tumor and its recurrence/metastasis.
- Most often encountered in the retroperitoneum.
- Transition from well-differentiated LPS to non-lipogenic sarcoma (image A) & (image B).
- Lipogenic component shows atypical fat with lipoblasts.
- Non-lipogenic sarcoma appears variable, can be high-grade (e.g. pleomorphic sarcoma, myxofibrosarcoma) or low grade (e.g. fibroblastic) spindle cells.
- A subset will show heterologous differentiation (rhabdomyosacoma, leiomyosarcoma, osteo- or chondrosarcoma, angiosarcoma).
- Like well-differentiated LPS shows amplified sequence of Chr 12q14-15.
- Immunohistochemistry: S100+, MDM2+ and CDK4+; keratin-.
- Poor prognosis, local recurrence in up to 40% and metastisis in 20% of cases.
- Retroperitoneal LPS may extend into the kidney and simulates a primary renal malignancy, particularly:
- RCC with sarcomatoid change: look for well differentiated (non-transformed) areas of RCC; keratin+, MDM-, CDK4-.
- Muscle predominant angiomyolipoma: mature fat and with abnormal thick hyalinized vessels; HMB45+.
- Examine "normal fat" around the tumor/kidney, which may represent well-differentiated LPS of the dedifferentiated LPS.
- Leiomyosarcoma: spindle cells with cigar-shaped nuclei; actin and desmin+; MDM and CDK4-.