title: [Parosteal osteosarcomas: unusual findings].
abstract: OBJECTIVE
  To study and evaluate the unusual findings in the natural history of parosteal osteosarcomas. Parosteal osteosarcomas are well-differentiated tumours of low grade malignancy, but may dedifferentiate into a more aggressive lesion.
  
  
  METHODS
  We reviewed 7 parosteal osteosarcomas treated in La Paz Hospital between 2005 and 2009 (3 were dedifferentiated parosteal osteosarcomas). The authors analysed the clinical and radiological features, histology, treatment and outcomes in this patient group.
  
  
  RESULTS
  There were 5 men and 2 women, with a mean age of 32.14 years, range 24-47 years. Three of seven tumours (42.8%) were dedifferentiated osteosarcomas. All three patients received chemotherapy. One patient presented with pulmonary metastases. No patient died.
  
  
  CONCLUSIONS
  It is important to understand that the biological phenomenon of dedifferentiation can occur in parosteal osteosarcomas. The prognosis, treatment and survival changes radically.
authors.affiliation: Unidad de Tumores Musculoesqueléticos, Servicio de Cirugía Ortopédica y Traumatología, Hospital Universitario La Paz, Madrid, España.
authors.forename: C A
authors.initials: CA
authors.lastname: Encinas-Ullán
authors.forename: E J
authors.initials: EJ
authors.lastname: Ortiz-Cruz
authors.forename: I
authors.initials: I
authors.lastname: Barrientos-Ruiz
authors.forename: M
authors.initials: M
authors.lastname: Valencia-Mora
authors.forename: J M
authors.initials: JM
authors.lastname: González-López
mesh_terms: D000328:Adult; D000970:Antineoplastic Agents / Q000627:therapeutic use; D017024:Chemotherapy, Adjuvant; D005260:Female; D005266:Femoral Neoplasms / Q000175:diagnosis* / Q000188:drug therapy / Q000601:surgery; D006801:Humans; D006811:Humerus / Q000000981:diagnostic imaging / Q000473:pathology; D008297:Male; D008875:Middle Aged; D018217:Osteosarcoma, Juxtacortical / Q000175:diagnosis* / Q000188:drug therapy / Q000601:surgery; D011859:Radiography; D012189:Retrospective Studies; D016896:Treatment Outcome
chemical_list: D000970:Antineoplastic Agents