title: p-Glycoprotein expression as a predictor of breast cancer recurrence.
abstract: BACKGROUND
  Many new prognostic factors for breast cancer have been described, and yet the ability to predict patient outcomes remains poor. Overexpression of p-glycoprotein (p-gp), the multidrug resistance efflux pump, confers a worse prognosis to patients with certain leukemias and other tumors. The purpose of this study was to analyze the potential usefulness of p-gp expression as a prognostic factor in patients with breast cancer.
  
  
  METHODS
  Paraffin blocks were obtained from 55 previously untreated patients who underwent surgery between 1987 and 1988. To determine p-gp expression, tumor cell suspensions were incubated with the p-gp-specific C219 monoclonal antibody and analyzed using an indirect immunofluorescent flow cytometric assay.
  
  
  RESULTS
  Twenty-four (44%) of the tumors were p-gp positive and 31 (56%) were p-gp negative. Among the p-gp positive patients, 65% had recurrence of their disease, whereas only 13% of the p-gp negative patients experienced recurrence (p = 0.0001). The 5-year disease-free rate for p-gp positive patients was 39% compared with 83% for p-gp negative patients (p = 0.0001). In univariate analysis examining 10 different variables, significant predictors of recurrence were p-gp, stage, and tumor size. Multivariate analysis using Cox Proportional Hazards regression showed that only p-gp and stage were significant independent predictors of recurrence (p = 0.0002).
  
  
  CONCLUSIONS
  p-gp is frequently expressed in patients with untreated breast cancer, with p-gp-positive patients being at significantly greater risk for disease recurrence. p-gp appears to be a useful prognostic factor in breast cancer and could potentially help guide management.
authors.affiliation: Department of General Surgery, Eastern Virginia Medical School, Norfolk, USA.
authors.forename: S
authors.initials: S
authors.lastname: Gregorcyk
authors.forename: Y
authors.initials: Y
authors.lastname: Kang
authors.forename: D
authors.initials: D
authors.lastname: Brandt
authors.forename: P
authors.initials: P
authors.lastname: Kolm
authors.forename: G
authors.initials: G
authors.lastname: Singer
authors.forename: R R
authors.initials: RR
authors.lastname: Perry
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000368:Aged; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000628:therapy; D003131:Combined Modality Therapy; D005260:Female; D005434:Flow Cytometry; D005500:Follow-Up Studies; D006801:Humans; D008875:Middle Aged; D009367:Neoplasm Staging; D011379:Prognosis; D016016:Proportional Hazards Models; D012008:Recurrence; D012189:Retrospective Studies
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1