title: Gene expression profiling spares early breast cancer patients from adjuvant therapy: derived and validated in two population-based cohorts.
abstract: BACKGROUND
  Adjuvant breast cancer therapy significantly improves survival, but overtreatment and undertreatment are major problems. Breast cancer expression profiling has so far mainly been used to identify women with a poor prognosis as candidates for adjuvant therapy but without demonstrated value for therapy prediction.
  
  
  METHODS
  We obtained the gene expression profiles of 159 population-derived breast cancer patients, and used hierarchical clustering to identify the signature associated with prognosis and impact of adjuvant therapies, defined as distant metastasis or death within 5 years. Independent datasets of 76 treated population-derived Swedish patients, 135 untreated population-derived Swedish patients and 78 Dutch patients were used for validation. The inclusion and exclusion criteria for the studies of population-derived Swedish patients were defined.
  
  
  RESULTS
  Among the 159 patients, a subset of 64 genes was found to give an optimal separation of patients with good and poor outcomes. Hierarchical clustering revealed three subgroups: patients who did well with therapy, patients who did well without therapy, and patients that failed to benefit from given therapy. The expression profile gave significantly better prognostication (odds ratio, 4.19; P = 0.007) (breast cancer end-points odds ratio, 10.64) compared with the Elston-Ellis histological grading (odds ratio of grade 2 vs 1 and grade 3 vs 1, 2.81 and 3.32 respectively; P = 0.24 and 0.16), tumor stage (odds ratio of stage 2 vs 1 and stage 3 vs 1, 1.11 and 1.28; P = 0.83 and 0.68) and age (odds ratio, 0.11; P = 0.55). The risk groups were consistent and validated in the independent Swedish and Dutch data sets used with 211 and 78 patients, respectively.
  
  
  CONCLUSIONS
  We have identified discriminatory gene expression signatures working both on untreated and systematically treated primary breast cancer patients with the potential to spare them from adjuvant therapy.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden. Yudi.Pawitan@meb.ki.se
authors.forename: Yudi
authors.initials: Y
authors.lastname: Pawitan
authors.forename: Judith
authors.initials: J
authors.lastname: Bjöhle
authors.forename: Lukas
authors.initials: L
authors.lastname: Amler
authors.forename: Anna-Lena
authors.initials: AL
authors.lastname: Borg
authors.forename: Suzanne
authors.initials: S
authors.lastname: Egyhazi
authors.forename: Per
authors.initials: P
authors.lastname: Hall
authors.forename: Xia
authors.initials: X
authors.lastname: Han
authors.forename: Lars
authors.initials: L
authors.lastname: Holmberg
authors.forename: Fei
authors.initials: F
authors.lastname: Huang
authors.forename: Sigrid
authors.initials: S
authors.lastname: Klaar
authors.forename: Edison T
authors.initials: ET
authors.lastname: Liu
authors.forename: Lance
authors.initials: L
authors.lastname: Miller
authors.forename: Hans
authors.initials: H
authors.lastname: Nordgren
authors.forename: Alexander
authors.initials: A
authors.lastname: Ploner
authors.forename: Kerstin
authors.initials: K
authors.lastname: Sandelin
authors.forename: Peter M
authors.initials: PM
authors.lastname: Shaw
authors.forename: Johanna
authors.initials: J
authors.lastname: Smeds
authors.forename: Lambert
authors.initials: L
authors.lastname: Skoog
authors.forename: Sara
authors.initials: S
authors.lastname: Wedrén
authors.forename: Jonas
authors.initials: J
authors.lastname: Bergh
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000601:surgery; D017024:Chemotherapy, Adjuvant; D015331:Cohort Studies; D005260:Female; D020869:Gene Expression Profiling; D052138:Genes, Neoplasm; D006801:Humans; D008875:Middle Aged; D009362:Neoplasm Metastasis; D009426:Netherlands; D016017:Odds Ratio; D011379:Prognosis; D016019:Survival Analysis; D013548:Sweden; D016896:Treatment Outcome