title: Relationship between histopathological features of chemotherapy treated retinoblastoma and P-glycoprotein expression.
abstract: BACKGROUND
  P-glycoprotein (P-gp) has been identified as a possible mediator of chemoresistance in retinoblastoma. The aim of this study was to determine the expression of P-gp in retinoblastoma treated with chemotherapy prior to enucleation.
  
  
  METHODS
  Seventeen enucleated specimens of retinoblastoma from 16 patients were studied. Nine had been treated with chemotherapy alone, and eight had been treated with chemotherapy and other forms of local treatment. Tumour differentiation as well as choroidal and optic nerve invasion were assessed. P-gp immunohistochemical staining was performed and evaluated as negative, low or high.
  
  
  RESULTS
  Histopathological assessment of the cases showed that 14 of 17 eyes (82.3%) had viable retinoblastoma cells. Nine retinoblastomas were considered regressed with a well-differentiated component, five regressed retinoblastomas had viable cells with poor differentiation and three retinoblastomas had regressed leaving no viable cells. Sixteen of 17 retinoblastomas were P-gp positive. In the one case with optic nerve invasion and the three cases with massive choroidal invasion, P-gp expression was found in invading retinoblastoma cells.
  
  
  CONCLUSIONS
  Almost all retinoblastomas expressed P-gp. High levels of P-gp expression might play a role in chemotherapy resistance of retinoblastoma or, conversely, chemotherapy might induce P-gp expression. These results might have an impact on management of bilateral retinoblastoma.
authors.affiliation: Departmentof Ophthalmology, Federal University of São Paulo, SãoPaulo, Brazil. jpessoafilho@hotmail.com
authors.forename: João P
authors.initials: JP
authors.lastname: Souza Filho
authors.forename: Maria C
authors.initials: MC
authors.lastname: Martins
authors.forename: Amanda L
authors.initials: AL
authors.lastname: Caissie
authors.forename: Virginia L L
authors.initials: VL
authors.lastname: Torres
authors.forename: Luiza H C F
authors.initials: LH
authors.lastname: Fernandes
authors.forename: Clelia M
authors.initials: CM
authors.lastname: Erwenne
authors.forename: Miguel N
authors.initials: MN
authors.lastname: Burnier
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D001918:Brachytherapy; D016190:Carboplatin / Q000008:administration & dosage; D002675:Child, Preschool; D003131:Combined Modality Therapy; D005047:Etoposide / Q000008:administration & dosage; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D007223:Infant; D008297:Male; D009361:Neoplasm Invasiveness; D019572:Retinal Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology*; D012175:Retinoblastoma / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology*; D014750:Vincristine / Q000008:administration & dosage
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D014750:Vincristine; D005047:Etoposide; D016190:Carboplatin