Case History

A 50-year-old male presents with a 9 cm retroperitoneal mass who had a resection of 16 cm fatty retroperitoneal mass 10 years prior.

Which of the following will show diffuse positivity in this tumor?

  1.       S100
  2.       SMA
  3.       MDM2
  4.       Desmin

Figure 1 Figure 2 Figure 3 Figure 4

Answer:

C. MDM2

Brief explanation of the answer:

The prior resection is a well-differentiated liposarcoma. The current 9 cm tumor is a dedifferentiated liposarcoma. While SMA and Desmin may show some variable staining in heterologous elements in these tumors, only MDM2 would be diffusely positive. MDM2 is diffusely positive in both well-differentiated liposarcomas and dedifferentiated liposarcomas. S100 is negative in these tumors. The main differential would consist of an undifferentiated pleomorphic sarcoma, myxofibrosarcoma, myxoid liposarcoma, pleomorphic liposarcoma, leiomyosarcoma, and malignant peripheral nerve sheath tumor.

Case contributed by Scott Taylor, M.D., Surgical Pathology Fellow, UAB Department of Pathology