title: Classical osteoblastoma, atypical osteoblastoma, and osteosarcoma: a comparative study based on clinical, histological, and biological parameters.
abstract: OBJECTIVE
  To investigate the biological behavior of classical and atypical osteoblastomas in comparison to osteosarcomas.
  
  
  METHODS
  Based on histological parameters, 30 osteoblastomas were subclassified as classical osteoblastomas (23/30) or atypical osteoblastoma (high cellularity, prominent blue osteoid, and epithelioid osteoblasts--7/30). Comparative immunohistochemical and clinical analysis was performed in 17 cases of patients with high-grade osteosarcoma. Formalin-fixed, paraffin-embedded archival tissue was immunostained for p53 and proliferation cell nuclear antigen. Tumors with positive p53 stain underwent molecular analyses for fragments of exon 10.
  
  
  RESULTS
  The mean proliferating cell nuclear antigen indexes for classical osteoblastoma, atypical osteoblastoma, and osteosarcoma were 33%, 61%, and 79%, respectively. The atypical subgroup showed similar results to those of the osteosarcoma group (P < 0.001). p53 protein was detected in 4 (13%) osteoblastomas (3 of these were atypical osteoblastoma), and 4 osteosarcomas (23%) also showed p53 positivity. DNA mutation performed in p53-positive cases was confirmed in exon 10 in 2 atypical osteoblastomas (2/3), 1 classical osteoblastoma (1/1), and 1 osteosarcoma (1/4). Disease recurrence was correlated with p53 expression (P = 0.009), atypical subtype (P = 0.031), spiculated blue bone on histology (P = 0.018), and proliferating-cell nuclear antigen labeling index > or =40 (P = 0.015).
  
  
  CONCLUSIONS
  These results validate atypical osteoblastoma as an entity, with p53 and proliferation cell nuclear antigen immuno-expression closer to that of osteosarcoma than of classical osteoblastoma. Proliferating cell nuclear antigen labeling index and p53 may be useful predictors of recurrence.
authors.affiliation: Department of Pathology, Orthopaedics and Traumatology Institute, Medical School, São Paulo University, São Paulo, SP, Brazil.
authors.forename: Cláudia Regina Gomes Cardim Mendes de
authors.initials: CR
authors.lastname: Oliveira
authors.forename: Berenice Bilharino
authors.initials: BB
authors.lastname: Mendonça
authors.forename: Olavo Pires de
authors.initials: OP
authors.lastname: Camargo
authors.forename: Emilia Modolo
authors.initials: EM
authors.lastname: Pinto
authors.forename: Sérgio Antonio Barbosa
authors.initials: SA
authors.lastname: Nascimento
authors.forename: Maria do Rosario D O
authors.initials: Mdo R
authors.lastname: Latorre
authors.forename: Maria Claúdia Nogueira
authors.initials: MC
authors.lastname: Zerbini
mesh_terms: D000293:Adolescent; D000328:Adult; D001859:Bone Neoplasms / Q000235:genetics / Q000276:immunology / Q000473:pathology*; D002648:Child; D002675:Child, Preschool; D004252:DNA Mutational Analysis; D005260:Female; D020869:Gene Expression Profiling; D016158:Genes, p53 / Q000235:genetics*; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D009154:Mutation / Q000235:genetics*; D018215:Osteoblastoma / Q000235:genetics / Q000276:immunology / Q000473:pathology*; D012516:Osteosarcoma / Q000235:genetics / Q000276:immunology / Q000473:pathology*; D016133:Polymerase Chain Reaction; D018809:Proliferating Cell Nuclear Antigen / Q000032:analysis* / Q000235:genetics; D012189:Retrospective Studies
chemical_list: D018809:Proliferating Cell Nuclear Antigen