title: Perivascular epitheloid cell tumour (PEComa) of the retroperitoneum - a rare tumor with uncertain malignant behaviour: a case report.
abstract: BACKGROUND
  Perivascular epitheloid cell tumours are rare mesenchymal neoplasms characterized by a proliferation of perivascular cells with an epitheloid phenotype and expression of myomelanocytic markers.
  
  
  METHODS
  Here we present the case of a cystic perivascular epitheloid cell tumour of the retroperitoneum associated with multifocal lung lesions. A 27-year-old woman underwent laparotomy to remove a 10 x 6 x 4 cm sized retroperitoneal mass. The resected specimen was subjected to frozen and permanent histological sections with conventional and immunohistochemical stains, including antibodies against HMB45. The tumour displayed the typical morphological and immunohistochemical features of a perivascular epitheloid cell tumour. Focal necrosis and a proliferative index of 10% suggested a malignant potential. Moreover, postoperative computed tomography scans demonstrated multiple lung lesions, which were radiologically interpreted as being most likely compatible with lymphangioleiomyomatosis.
  
  
  CONCLUSIONS
  Since lymphangioleiomyomatosis, an otherwise benign condition, belongs to the family of perivascular epitheloid cell tumours, it cannot be excluded that the lung lesions in this case in fact represent metastases from the retroperitoneal perivascular epitheloid cell tumour rather than independent neoplasms. More experience with this new and unusual tumour entity is clearly needed in order to define reliable criteria for benign or malignant behaviour.
authors.affiliation: Department of General, Visceral and Thoracic Surgery, University Medical Centre of Hamburg-Eppendorf, Martinistrasse 52, Hamburg, Germany. akoenig@uke.uni-hamburg.de.
authors.forename: Alexandra M
authors.initials: AM
authors.lastname: Koenig
authors.forename: Alexander
authors.initials: A
authors.lastname: Quaas
authors.forename: Thorsten
authors.initials: T
authors.lastname: Ries
authors.forename: Emre F
authors.initials: EF
authors.lastname: Yekebas
authors.forename: Karim A
authors.initials: KA
authors.lastname: Gawad
authors.forename: Yogesh K
authors.initials: YK
authors.lastname: Vashist
authors.forename: Christoph
authors.initials: C
authors.lastname: Burdelski
authors.forename: Oliver
authors.initials: O
authors.lastname: Mann
authors.forename: Jakob R
authors.initials: JR
authors.lastname: Izbicki
authors.forename: Andreas
authors.initials: A
authors.lastname: Erbersdobler