Atypical Lipomatous Tumor/Well-Diff Liposarcoma : MDM2 FISH

Comments:
Real-time PCR and FISH for amplification of MDM2 are highly sensitive and specific for the diagnosis of atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) and dedifferentiated liposarcoma and their distinction from benign lipomatous tumors and soft tissue sarcomas respectively.

MDM2 FISH is more reliable and superior to MDM2 immunohistochemistry which has low sensitivity and a small false-positive rate. A small percentage of spindle cell/pleomorphic lipomas may be MDM2 FISH positive due to polysomy of 12q locus.

MDM2 FISH is extremely useful in evaluation of lipomatous lesions in older patients (>50 yrs.) in the following circumstances: lipomatous tumors with borderline cytologic atypia, recurrent lipomas, deep-seated large lipomas (>10 cm), retroperitoneal or intraabdominal lipomatous tumors without atypia.

This FISH image shows MDM2 amplification (red) in a case of ALT/WDL. CEP12-SG (green) is a reference probe for the centromeric region of chromosome 12. Image courtesy of: Dr. Runjan Chetty (@RunjanChetty); used with permission.