title: Review of the clinical studies using the 21-gene assay.
abstract: OBJECTIVE
  A major challenge in treating early-stage hormone receptor (HR)(+) breast cancer is selecting women who, after initial surgery, do not require chemotherapy. Better prognostic and predictive tests are needed. The 21-gene assay is the only widely commercially available gene signature that can be performed on formalin-fixed paraffin-embedded tissue.
  
  
  METHODS
  We conducted a review of the literature supporting the prognostic and predictive ability of the 21-gene assay in HR(+) node-negative and node-positive breast cancer patients in chemotherapy-/endocrine-treated and untreated populations. We considered: (a) How accurate is the recurrence score (RS) as a prognostic factor for distant recurrence? (b) How accurate is the RS as a predictive factor for benefit from systemic therapy? (c) How does the RS compare with other prognostic/predictive factors such as tumor size, tumor grade, patient age, and integrated decision aids such as Adjuvant! Online? (d) How do patients and physicians view the 21-gene assay? (e) What are the cost implications of the 21-gene assay?
  
  
  RESULTS
  The 21-gene assay: (a) provided accurate risk information; (b) predicted response to cyclophosphamide, methotrexate, and 5-fluorouracil and to cyclophosphamide, doxorubicin, and 5-fluorouracil chemotherapy; (c) added additional information to traditional biomarkers; (d) was viewed positively by both physicians and patients; and (e) fell within the cost-effectiveness values in North America.
  
  
  CONCLUSIONS
  This assay may be offered to patients with node-negative HR(+) breast cancer to assist in adjuvant treatment decisions. Data are accumulating to support the use of the 21-gene assay in HR(+) node-positive patients.
authors.affiliation: Division of Medical Oncology, Sunnybrook Odette Cancer Centre, The University of Toronto, Toronto, Ontario, Canada, M4N 3M5.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Kelly
authors.forename: Ellen
authors.initials: E
authors.lastname: Warner
authors.forename: Daphne T
authors.initials: DT
authors.lastname: Tsoi
authors.forename: Sunil
authors.initials: S
authors.lastname: Verma
authors.forename: Kathleen I
authors.initials: KI
authors.lastname: Pritchard
mesh_terms: D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology / Q000601:surgery; D017024:Chemotherapy, Adjuvant; D003362:Cost-Benefit Analysis; D005260:Female; D015870:Gene Expression; D052138:Genes, Neoplasm; D006801:Humans; D008207:Lymphatic Metastasis; D009364:Neoplasm Recurrence, Local / Q000175:diagnosis* / Q000235:genetics; D018579:Patient Selection; D011379:Prognosis; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000191:economics / Q000379:methods*; D012680:Sensitivity and Specificity; D016896:Treatment Outcome