A pathologist receives a biopsy from a retroperitoneal mass. Histology shows intersecting fascicles of spindle cells with a herringbone pattern and frequent mitoses. IHC: desmin positive, myogenin negative, SMA negative, S100 negative. Molecular testing reveals a MDM2 gene amplification. What is the most likely diagnosis?
- A Leiomyosarcoma
- B Embryonal rhabdomyosarcoma
- C Well-differentiated liposarcoma / dedifferentiated liposarcoma ✓
- D Fibrosarcoma
Correct answer: C. Well-differentiated liposarcoma / dedifferentiated liposarcoma
Explanation
MDM2 amplification (12q13-15) is the hallmark molecular event in well-differentiated and dedifferentiated liposarcoma; the dedifferentiated component appears as a high-grade spindle cell sarcoma that has lost lipogenic differentiation markers. Desmin positivity can occur focally in dedifferentiated liposarcoma. Leiomyosarcoma shows desmin and SMA positivity but lacks MDM2 amplification. Rhabdomyosarcoma would be myogenin-positive. Fibrosarcoma is a diagnosis of exclusion without specific molecular markers.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.