CHOP Is Not Rearranged in Epithelioid Pleomorphic Liposarcoma. Fluorescence In Situ Hybridization (FISH) Study on Four Cases
J Lasota, J Marwaha, JC Fanburg-Smith. Armed Forces Institute of Pathology, Washington, DC
Background: Epithelioid pleomorphic liposarcoma (EPL), a morphoplogic subtype of the rare aggressive pleomorphic liposarcoma, has no known consistent chromosomal aberration. Particularly the epithelioid variant, with its sheets of mono- to multivacuolated lipoblasts, may occasionally have morphologic overlap with mxyoid/round cell liposarcoma. A case report of EPL demonstrated FUS-CHOP fusion gene transcripts by RT-PCR and postulated it to be part of the myxoid-round cell liposarcoma spectrum, a tumor known to be positive for t(12;16)(q13;p11) resulting in FUS-CHOP fusion gene or less commonly t(12;22)(q13;q12) resulting in EWS-CHOP fusion gene. In this study, additional cases of epithelioid pleomorphic liposarcoma were evaluated for CHOP rearrangements.
Design: Four cases of epithelioid pleomorphic liposarcoma with available block, slides, and folder were retrieved from AFIP files. All tumors were evaluated for CHOP rearrangements using FISH and dual color, break apart CHOP rearrangement probe (Abbott Molecular, US).
Results: Four epithelioid pleomorphic liposarcomas (3M:1F) were included. The patients ranged from 42 to 78 years with a mean age of 60.5 years. Tumor size ranged from 1.5 cm - 15 cm, mean 9.3 cm. Locations included buttock, shoulder, chest, and thigh, the latter with a known metastasis to chest wall. All tumors had sheets of large bizarre monovacuolated to multivacuolated lipoblasts, with necrosis and increased mitotic activity, including abnormal forms. One case demonstrated transition to spindled malignant fibrous histiocytomalike areas. Delicate vasculature, myxoid change, stellate or small round cells were not observed. All tumors were focally positive for S100 protein and negative for pankeratin, CK18, CK8, CK7, CK20, EMA, CD34, and chromogranin. One case had focal reactivity for desmin and HMB45, suggesting a potential immunophenotypic overlap with malignant PEComa. None of the four epithelioid pleomorphic liposarcomas studied by FISH demonstrated CHOP rearrangements.
Conclusions: Although a case report of epithelioid pleomorphic liposarcoma demonstrated FUS-CHOP fusion gene transcripts by RT-PCR and postulated it to be part of the myxoid-round cell liposarcoma spectrum, in our series, epithelioid pleomorphic liposarcoma does not demonstrate CHOP rearrangement by FISH. Based on this genetic finding, epithelioid pleomorphic liposarcoma should be considered separate from the myxoid-round cell liposarcoma spectrum of tumors.
Category: Bone & Soft Tissue
Monday, March 9, 2009 1:00 PM
Poster Session II # 1, Monday Afternoon