title: Molecular classification of tamoxifen-resistant breast carcinomas by gene expression profiling.
abstract: OBJECTIVE
  To discover a set of markers predictive for the type of response to endocrine therapy with the antiestrogen tamoxifen using gene expression profiling.
  
  
  METHODS
  The study was performed on 112 estrogen receptor-positive primary breast carcinomas from patients with advanced disease and clearly defined types of response (ie, 52 patients with objective response v 60 patients with progressive disease) from start of first-line treatment with tamoxifen. Main clinical end points are the effects of therapy on tumor size and time until tumor progression (progression-free survival [PFS]). RNA isolated from tumor samples was amplified and hybridized to 18,000 human cDNA microarrays.
  
  
  RESULTS
  Using a training set of 46 breast tumors, 81 genes were found to be differentially expressed (P < or = .05) between tamoxifen-responsive and -resistant tumors. These genes were involved in estrogen action, apoptosis, extracellular matrix formation, and immune response. From the 81 genes, a predictive signature of 44 genes was extracted and validated on an independent set of 66 tumors. This 44-gene signature is significantly superior (odds ratio, 3.16; 95% CI, 1.10 to 9.11; P = .03) to traditional predictive factors in univariate analysis and also significantly related with a longer PFS in univariate (hazard ratio, 0.54; 95% CI, 0.31 to 0.94; P = .03) as well as in multivariate analyses (P = .03).
  
  
  CONCLUSIONS
  Our data show that gene expression profiling can be used to discriminate between breast cancer patients with progressive disease and objective response to tamoxifen. Additional studies are needed to confirm if the predictive signature might allow identification of individual patients who could benefit from other (adjuvant) endocrine therapies.
authors.affiliation: Department of Medical Oncology, Erasmus MC/Daniel den Hoed Cancer Center, Rotterdam, The Netherlands.
authors.forename: Maurice P H M
authors.initials: MP
authors.lastname: Jansen
authors.forename: John A
authors.initials: JA
authors.lastname: Foekens
authors.forename: Iris L
authors.initials: IL
authors.lastname: van Staveren
authors.forename: Maaike M
authors.initials: MM
authors.lastname: Dirkzwager-Kiel
authors.forename: Kirsten
authors.initials: K
authors.lastname: Ritstier
authors.forename: Maxime P
authors.initials: MP
authors.lastname: Look
authors.forename: Marion E
authors.initials: ME
authors.lastname: Meijer-van Gelder
authors.forename: Anieta M
authors.initials: AM
authors.lastname: Sieuwerts
authors.forename: Henk
authors.initials: H
authors.lastname: Portengen
authors.forename: Lambert C J
authors.initials: LC
authors.lastname: Dorssers
authors.forename: Jan G M
authors.initials: JG
authors.lastname: Klijn
authors.forename: Els M J J
authors.initials: EM
authors.lastname: Berns
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000145:classification / Q000188:drug therapy / Q000235:genetics*; D019008:Drug Resistance, Neoplasm; D005260:Female; D020869:Gene Expression Profiling; D006801:Humans; D008875:Middle Aged; D013629:Tamoxifen / Q000627:therapeutic use*; D017211:Treatment Failure
chemical_list: D013629:Tamoxifen