title: Population-based analysis of the impact and generalizability of the NSABP-B24 study on endocrine therapy for patients with ductal carcinoma in situ of the breast.
abstract: BACKGROUND
  In 1999, the National Surgical Adjuvant Breast and Bowel Project (NSABP)-B24 trial demonstrated that tamoxifen reduced relapse risk in women with ductal carcinoma in situ (DCIS) treated with breast-conserving surgery (BCS) and radiotherapy (RT). In 2002, Allred's subgroup analysis showed that tamoxifen mainly benefitted estrogen receptor (ER)-positive disease. This study evaluates the impact and generalizability of these trial findings at the population level.
  
  
  METHODS
  From 1989 to 2009, 2061 women with DCIS underwent BCS + RT in British Columbia. The following cohorts were analyzed: (1) pre-NSABP-B24 era (1989-1998, N = 417); (2) post-NSABP-B24 era (2000-2009, N = 1548). Cohort 2 was further divided into pre- and post-Allred eras.
  
  
  RESULTS
  Endocrine therapy (ET) was used in 404/2061 (20%) patients. Median age of patients treated with compared with without ET, was 53 versus 57 years, (P < 0.0005). One of 417 (0.2%) versus 399/1548 (26%) patients took ET before versus after NSABP-B24. Among the post-Allred era cohort treated with ET (N = 227), tumors were ER-positive in 65%, ER-negative in 1%, and ER-unknown in 33%; whereas of those treated without ET (N = 801), ER was positive in 43%, negative in 15%, and unknown in 42% (P < 0.0005). On multivariable analysis of the post-NSABP-B24 era, ET was associated with improved event-free survival (EFS) (hazard ratio 0.6; P = 0.02); 5-year EFS were 96.9% with ET versus 94.5% without ET.
  
  
  CONCLUSIONS
  ET use in DCIS patients treated with BCS + RT increased significantly after the NSABP-B24 study. ER+ disease and younger age were associated with increased ET use. ET was associated with improved EFS, confirming the generalizability of trial data at a population level.
authors.affiliation: Department of Radiation Oncology, British Columbia Cancer Agency (BCCA), Vancouver; Faculty of Medicine, University of BC, Vancouver.
authors.forename: A C
authors.initials: AC
authors.lastname: Lo
authors.affiliation: Department of Radiation Oncology, British Columbia Cancer Agency (BCCA), Victoria; Breast Cancer Outcomes Unit, Vancouver; Faculty of Medicine, University of BC, Vancouver.
authors.forename: P T
authors.initials: PT
authors.lastname: Truong
authors.affiliation: Department of Radiation Oncology, British Columbia Cancer Agency (BCCA), Victoria; Breast Cancer Outcomes Unit, Vancouver; Faculty of Medicine, University of BC, Vancouver.
authors.forename: E S
authors.initials: ES
authors.lastname: Wai
authors.affiliation: Department of Radiation Oncology, British Columbia Cancer Agency (BCCA), Vancouver; Breast Cancer Outcomes Unit, Vancouver; Faculty of Medicine, University of BC, Vancouver.
authors.forename: A
authors.initials: A
authors.lastname: Nichol
authors.affiliation: Department of Radiation Oncology, British Columbia Cancer Agency (BCCA), Vancouver; Breast Cancer Outcomes Unit, Vancouver; Faculty of Medicine, University of BC, Vancouver.
authors.forename: L
authors.initials: L
authors.lastname: Weir
authors.affiliation: Breast Cancer Outcomes Unit, Vancouver.
authors.forename: C
authors.initials: C
authors.lastname: Speers
authors.affiliation: Department of Pathology, BCCA, Vancouver; Faculty of Medicine, University of BC, Vancouver.
authors.forename: M M
authors.initials: MM
authors.lastname: Hayes
authors.affiliation: Faculty of Medicine, University of BC, Vancouver; Department of Surgical Oncology, BCCA, Kelowna, Canada.
authors.forename: C
authors.initials: C
authors.lastname: Baliski
authors.affiliation: Department of Radiation Oncology, British Columbia Cancer Agency (BCCA), Vancouver; Breast Cancer Outcomes Unit, Vancouver; Faculty of Medicine, University of BC, Vancouver. Electronic address: styldesl@bccancer.bc.ca.
authors.forename: S
authors.initials: S
authors.lastname: Tyldesley
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000628:therapy*; D002285:Carcinoma, Intraductal, Noninfiltrating / Q000628:therapy*; D059248:Chemoradiotherapy / Q000379:methods*; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D015412:Mastectomy, Segmental; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local; D013629:Tamoxifen / Q000627:therapeutic use*
chemical_list: D018931:Antineoplastic Agents, Hormonal; D013629:Tamoxifen
keywords: breast; ductal carcinoma in situ; endocrine therapy; hormonal therapy; tamoxifen