Primary Retroperitoneal Myxoid Liposarcomas

Area of Science:

• Oncology
• Pathology
• Genetics

Background:

• Myxoid liposarcomas (MLSs) are typically found in extremities and defined by DDIT3 gene fusions.
• The primary origin of MLSs in the retroperitoneum is debated, with some cases potentially misidentified metastases or other liposarcoma subtypes.
• Distinguishing primary retroperitoneal MLSs from other liposarcomas with myxoid features, such as those with MDM2 amplifications, is clinically important.

Purpose of the Study:

• To investigate and confirm the occurrence of primary myxoid liposarcomas originating in the retroperitoneum.
• To establish diagnostic criteria for retroperitoneal MLSs through clinicopathologic and molecular evaluation.
• To differentiate primary retroperitoneal MLSs from other liposarcoma subtypes.

Main Methods:

• Clinicopathologic reevaluation of 5 cases of retroperitoneal liposarcomas with myxoid features.
• Histologic examination for classic myxoid liposarcoma findings.
• Fluorescence in situ hybridization (FISH) to detect DDIT3 gene rearrangements and MDM2 amplifications.

Main Results:

• Five cases of primary retroperitoneal MLSs were identified, representing 2.3% of primary retroperitoneal liposarcomas in the database.
• Patients (3 male, 2 female) had a median age of 32 years; tumors were localized to the retroperitoneum at presentation.
• All 5 cases showed focal classic histologic features, harbored DDIT3 gene rearrangements, and lacked MDM2 amplifications.

Conclusions:

• Primary myxoid liposarcomas can rarely originate in the retroperitoneum.
• Accurate diagnosis requires a combination of clinicopathologic assessment and molecular analysis (DDIT3 rearrangements).
• This study clarifies the existence of primary retroperitoneal MLSs, distinguishing them from metastatic disease or other liposarcoma subtypes.