[35] Spindle Cell Liposarcoma, a Distinct Entity or Histologic Variant? Histologic and Molecular Analysis of 12 Cases

Andrea T Deyrup, Frederic Chibon, Louis Guillou, Pauline Lagarde, Sharon W Weiss, Jean-Michel Coindre. USC-SOM, Greenville; Emory University, Atlanta; Institut Bergonie, Bordeaux, France; Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland

Background: Spindle cell (SC) liposarcomas (LPS), an incompletely characterized tumor, has been considered toa variant of myxoid LPS, well differentiated LPS or SC lipoma. Using strict morphologic criteria we analyzed a series of cases of SC-LPS to determine if clinical and molecular characteristics warrant its acceptance as a unique entity.
Design: Cases classified as "spindle cell LPS" or "low-grade LPS with spindle cell features" were identified from the authors' consultation and hospital files and reviewed by at least 3 authors. Diagnosis was based on 1) a low grade, monotonous SC component and 2) a population of typically mono- or binucleated lipoblasts with an "ice cream cone" appearance. CGH analysis and FISH for the DDIT3 fusion and MDM2 amplification were performed. A panel of immunohistochemical stains, including HMGA2, MDM2, CDK4, desmin, SMA, myogenin, MyoD1, S100 protein, CD34, and Ki-67, was evaluated. Clinical follow-up was obtained.
Results: Of 25 initially identified cases, 12 cases clearly met morphologic criteria; 6 cases were reclassified as low grade sarcoma, not further classified. CGH analysis of ambiguous cases excluded 5 cases as low-grade dedifferentiated LPS and 2 cases as SC lipoma. SC-LPS affected the sexes equally (6M:6F). Patients ranged from 15 to 82 years (mean 47). Tumors arose in the lower extremity (5), groin/vulva/paratesticular tissue (4), inguinal area (1), abdominal wall (1) and shoulder (1). Tumors ranged in size from 2 to 20 cm (mean 7.7 cm). CGH showed no gains or losses. No tumors showed MDM2 amplification or the DDIT3 fusion by FISH. By immunohistochemistry, the SC-LPS expressed CD34 (10/12), S100 protein (7/12) and desmin (3/12); other antigens were negative. Proliferation was low (Ki-67 1-3%). Clinical follow-up was obtained for 10 patients (range, 9-113 mos; mean, 47mos): 1 patient developed bone metastasis at 111 mos but is alive with disease; the remaining patients had no recurrence or metastasis.
Conclusions: Spindle cell liposarcoma is a distinct form of liposarcoma having a characteristic morphologic appearance, a flat CGH profile and indolent behavior. Since late metastases can be seen, long term follow up is needed to assess full metastatic potential. Some features of SC-LPS overlap with low-grade DDL, which is clinically more aggressive, and SC lipoma, which is benign, indicating the need for molecular-genetic studies in histologically ambiguous cases.
Category: Bone & Soft Tissue

Monday, March 19, 2012 1:00 PM

Poster Session II # 11, Monday Afternoon


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