Dedifferentiated liposarcoma composed predominantly of rhabdoid/epithelioid cells: a frequently misdiagnosed highly aggressive variant

Publication date: Available online 5 January 2018
Source:Human Pathology
Author(s): Abbas Agaimy, Michael Michal, Ladislav Hadravsky, Michal Michal
Dedifferentiated liposarcoma is one of the most common sarcoma types in adults with a predilection for the retroperitoneum. We have recently encountered 6 cases of DDL composed predominantly of rounded, rhabdoid or epithelioid cells mimicking rhabdoid melanoma, epithelioid rhabdomyosarcoma or undifferentiated carcinoma. Patients were 5 males and one female aged 64 to 81 years (median, 68). Tumors originated in the retroperitoneum (n=5; 3 in the psoas muscle) and deep soft tissue of the thigh (n=1). All 3 patients with follow-up died of metastatic disease within 4 to 8 months. Preoperative biopsy diagnoses never suggested dedifferentiated liposarcoma as a possibility; instead carcinoma, rhabdomyosarcoma and lymphoma were on top of suggestions. Five resected tumors were composed predominantly (70-100%) of anaplastic rounded to oval rhabdoid cells with prominent central nucleoli and paranuclear rhabdoid inclusions. Bi- and multinucleation was a constant feature. The background stroma showed variable myxoid changes and minor mixed inflammatory cells. Two cases showed homologous dedifferentiation and another had sclerosing spindle cell nodule but a well differentiated lipomatous component was not seen in any. One biopsied case showed solely monotonous small round blue cells with scattered rhabdoid cells. Immunohistochemistry showed expression of MDM2 (6/6), CDK4 (5/6), pancytokeratin AE/1AE3 (4/6) and diffusely desmin + myogenin (2/6). All cases showed high-level co-amplification of MDM2/CDK4 by in-situ-hybridization. The SWI/SNF complex components (SMARCB1, SMARCA2, SMARCA4, ARID1A and PBRM1) were intact in all cases. This highly aggressive liposarcoma variant needs to be distinguished from a variety of neoplasms including undifferentiated carcinoma, melanoma, lymphoma, rhabdomyosarcoma and others.



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