title: Design, conduct, and analyses of Breast International Group (BIG) 1-98: a randomized, double-blind, phase-III study comparing letrozole and tamoxifen as adjuvant endocrine therapy for postmenopausal women with receptor-positive, early breast cancer.
abstract: BACKGROUND
  Aromatase inhibitors provide superior disease control when compared with tamoxifen as adjuvant therapy for postmenopausal women with endocrine-responsive early breast cancer.
  
  
  OBJECTIVE
  To present the design, history, and analytic challenges of the Breast International Group (BIG) 1-98 trial: an international, multicenter, randomized, double-blind, phase-III study comparing the aromatase inhibitor letrozole with tamoxifen in this clinical setting.
  
  
  METHODS
  From 1998-2003, BIG 1-98 enrolled 8028 women to receive monotherapy with either tamoxifen or letrozole for 5 years, or sequential therapy of 2 years of one agent followed by 3 years of the other. Randomization to one of four treatment groups permitted two complementary analyses to be conducted several years apart. The first, reported in 2005, provided a head-to-head comparison of letrozole versus tamoxifen. Statistical power was increased by an enriched design, which included patients who were assigned sequential treatments until the time of the treatment switch. The second, reported in late 2008, used a conditional landmark approach to test the hypothesis that switching endocrine agents at approximately 2 years from randomization for patients who are disease-free is superior to continuing with the original agent.
  
  
  RESULTS
  The 2005 analysis showed the superiority of letrozole compared with tamoxifen. The patients who were assigned tamoxifen alone were unblinded and offered the opportunity to switch to letrozole. Results from other trials increased the clinical relevance about whether or not to start treatment with letrozole or tamoxifen, and analysis plans were expanded to evaluate sequential versus single-agent strategies from randomization.
  
  
  CONCLUSIONS
  Due to the unblinding of patients assigned tamoxifen alone, analysis of updated data will require ascertainment of the influence of selective crossover from tamoxifen to letrozole.
  
  
  CONCLUSIONS
  BIG 1-98 is an example of an enriched design, involving complementary analyses addressing different questions several years apart, and subject to evolving analytic plans influenced by new data that emerge over time.
authors.affiliation: International Breast Cancer Study Group Statistical Center, Department of Biostatistics and Computational Biology, Dana-Farber Cancer Institute, Boston, MA 02115, USA. agiohur@jimmy.harvard.edu
authors.forename: Anita
authors.initials: A
authors.lastname: Giobbie-Hurder
authors.forename: Karen N
authors.initials: KN
authors.lastname: Price
authors.forename: Richard D
authors.initials: RD
authors.lastname: Gelber
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use*; D047072:Aromatase Inhibitors / Q000627:therapeutic use*; D014408:Biomarkers, Tumor / Q000097:blood; D001943:Breast Neoplasms / Q000097:blood / Q000188:drug therapy*; D017024:Chemotherapy, Adjuvant; D004311:Double-Blind Method; D004359:Drug Therapy, Combination; D004965:Estrogen Antagonists / Q000627:therapeutic use; D005260:Female; D006801:Humans; D000077289:Letrozole; D009570:Nitriles / Q000627:therapeutic use*; D017698:Postmenopause; D011960:Receptors, Estrogen / Q000097:blood*; D012107:Research Design; D013629:Tamoxifen / Q000627:therapeutic use*; D016896:Treatment Outcome; D014230:Triazoles / Q000627:therapeutic use*
chemical_list: D018931:Antineoplastic Agents, Hormonal; D047072:Aromatase Inhibitors; D014408:Biomarkers, Tumor; D004965:Estrogen Antagonists; D009570:Nitriles; D011960:Receptors, Estrogen; D014230:Triazoles; D013629:Tamoxifen; D000077289:Letrozole