Atypical Lipomatous Tumor/Well-Differentiated Liposarcoma With Features Mimicking Spindle Cell Lipoma

Area of Science:

• Oncology
• Pathology
• Molecular Diagnostics

Background:

• Atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) and spindle cell lipoma are distinct lipomatous tumors.
• Histological and immunophenotypic overlap can complicate their differentiation.
• Distinct clinical behavior and prognosis necessitate accurate diagnosis.

Observation:

• A 69-year-old woman presented with a gluteal lipomatous tumor.
• The tumor showed features mimicking spindle cell lipoma, including CD34 positivity and RB1 loss.
• However, it also exhibited MDM2 and CDK4 amplification.

Findings:

• Fluorescence in situ hybridization confirmed MDM2 and CDK4 amplification.
• The molecular findings supported a diagnosis of ALT/WDL despite features suggestive of spindle cell lipoma.
• This case presents a rare instance of RB1 loss in a well-differentiated ALT/WDL.

Implications:

• This case highlights the importance of molecular analysis in atypical lipomatous tumor differentiation.
• MDM2/CDK4 amplification testing is recommended for lipomatous tumors resembling spindle cell lipoma.
• Accurate molecular diagnosis is critical for appropriate patient management and prognosis.