title: Challenging dedifferentiated liposarcoma identified by MDM2-amplification, a report of two cases.
abstract: BACKGROUND
  Liposarcoma is the most frequent soft tissue sarcoma. Well differentiated liposarcoma may progress into dedifferentiated liposarcoma with pleomorphic histology. A minority additionally features myogenic, osteo- or chondrosarcomatous heterologous differentiation. Genomic amplification of the Mouse double minute 2 homolog (MDM2) locus is characteristic for well differentiated and dedifferentiated liposarcomas. Detection of MDM2 amplification may supplement histopathology and aid to distinguish liposarcoma from other soft tissue neoplasia.
  
  
  METHODS
  Here we present two cases of dedifferentiated liposarcoma with challenging presentation. Case 1 features a myogenic component. As the tumour infiltrated the abdominal muscles and showed immunohistochemical expression of myogenic proteins, rhabdomyosarcoma had to be ruled out. Case 2 has an osteosarcomatous component resembling extraosseous osteosarcoma. The MDM2 status was determined in both cases and helped making the correct diagnosis. Overexpression of MDM2 and co-overexpression of Cyclin-dependent kinase 4 is demonstrated by immunohistochemistry. The underlying MDM2 amplification is shown by fluorescence in situ hybridisation. Since low grade osteosarcoma may also harbour MDM2 amplification it is emphasised that the amplification has to be present in the lipomatous parts of the tumour to distinguish liposarcoma from extraosseous osteosarcoma.
  
  
  CONCLUSIONS
  The two cases exemplify challenges in the diagnoses of dedifferentiated liposarcoma. Liposarcoma often has pleomorphic histology and additionally may feature heterologous components that mimic other soft tissue neoplasms. Amplification of MDM2 is characteristic for well differentiated and dedifferentiated liposarcomas. Determination of the MDM2 status by in situ hybridisation may assist histopathology and help to rule out differential diagnoses.
authors.affiliation: Institute of Pathology Nordhessen, Germaniastr. 7, 34119 Kassel, Germany.
authors.forename: Suvi
authors.initials: S
authors.lastname: Lokka
authors.affiliation: Institute of Pathology Nordhessen, Germaniastr. 7, 34119 Kassel, Germany.|Department of Pathology, University Medical Centre Göttingen, Robert-Koch-Str. 38, 37077 Göttingen, Germany.
authors.forename: Andreas H
authors.initials: AH
authors.lastname: Scheel
authors.affiliation: Rotes Kreuz Krankenhaus, Department of Surgery, Hansteinstrasse 29, 34121 Kassel, Germany.|Department of General, Visceral, and Paediatric Surgery, University Medical Centre Göttingen, Robert-Koch-Str. 38, 37077 Göttingen, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Dango
authors.affiliation: Department of Pathology, University Medical Centre Göttingen, Robert-Koch-Str. 38, 37077 Göttingen, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Schmitz
authors.affiliation: Rotes Kreuz Krankenhaus, Department of Surgery, Hansteinstrasse 29, 34121 Kassel, Germany.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Hesterberg
authors.affiliation: Institute of Pathology Nordhessen, Germaniastr. 7, 34119 Kassel, Germany.
authors.forename: Josef
authors.initials: J
authors.lastname: Rüschoff
authors.affiliation: Department of Pathology, University Medical Centre Göttingen, Robert-Koch-Str. 38, 37077 Göttingen, Germany.
authors.forename: Hans-Ulrich
authors.initials: HU
authors.lastname: Schildhaus
keywords: Dedifferentiated Liposarcoma; Fluorescence in situ hybridisation; Liposarcoma with osteoblastic component; MDM2