title: Prognostic relevance of P-glycoprotein expression in breast cancer.
abstract: BACKGROUND
  P-glycoprotein (Pgp) expression has been reported to be associated with a poor prognosis in some malignancies such as neuroblastoma, soft tissue sarcoma and acute myeloid leukemia. The prognostic role of Pgp expression in breast cancer is still unclear. We investigated the expression of Pgp in primary and metastatic breast cancer tissues in relation to patient characteristics and treatment outcome.
  
  
  METHODS
  Pgp expression was evaluated in 92 primary and 12 metastatic breast cancers by the use of immunohisto/cytochemistry with three monoclonal antibodies (MAbs) (JSB-1, C219, MRK16), and an RNAse protection assay. Follow-up information was available for 77 primary breast cancer patients (median follow-up 42 months; range 2-63 months).
  
  
  RESULTS
  Concordance among the anti-Pgp MAbs varied, the highest being between JSB-1 and MRK16 (71%; p=0.002). Pgp expression was more frequent in metastatic disease (58%) than in primary breast cancer (29%) (JSB-1; p=0.055). Pgp expression as assessed with JSB-1 (univariate analysis; p<0.05) was associated with shorter overall survival (OS). Nineteen (21%) primary breast cancers had Pgp expression in fibroblasts in desmoplastic stroma and this did not correlate with Pgp expression in the tumor. The combination of Pgp-positive tumor cells and Pgp-expressing fibroblasts was the strongest prognostic factor for OS by multivariate analysis. Subgroup analysis suggested that Pgp expression was associated with a shorter OS in tamoxifen-treated patients, but not in those who received chemotherapy (most often CMF).
  
  
  CONCLUSIONS
  Pgp expression in tumor cells, and especially when accompanied by Pgp expression in fibroblasts in desmoplastic stroma, has prognostic value in primary breast cancer patients and is likely to be a marker of a more malignant phenotype. Pgp expression of tumor cells might play a role in tamoxifen resistance. These findings may have important implications for teh treatment of breast cancer patients, and warrant further prospective investigation in a larger patient population.
authors.affiliation: Department of Medical Oncology, Free University Hospital, Amsterdam, The Netherlands.
authors.forename: S C
authors.initials: SC
authors.lastname: Linn
authors.forename: G
authors.initials: G
authors.lastname: Giaccone
authors.forename: P J
authors.initials: PJ
authors.lastname: van Diest
authors.forename: W M
authors.initials: WM
authors.lastname: Blokhuis
authors.forename: P
authors.initials: P
authors.lastname: van der Valk
authors.forename: C K
authors.initials: CK
authors.lastname: van Kalken
authors.forename: C M
authors.initials: CM
authors.lastname: Kuiper
authors.forename: H M
authors.initials: HM
authors.lastname: Pinedo
authors.forename: J P
authors.initials: JP
authors.lastname: Baak
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000328:Adult; D000368:Aged; D001940:Breast / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D005500:Follow-Up Studies; D006801:Humans; D007150:Immunohistochemistry; D008875:Middle Aged; D015999:Multivariate Analysis; D009362:Neoplasm Metastasis; D011379:Prognosis; D012044:Regression Analysis; D015996:Survival Rate
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1