title: Identification of patients at very low risk of local recurrence after breast-conserving surgery.
abstract: OBJECTIVE
  To identify clinical and pathological factors that identify groups of women with stage I breast cancer with a 5-year risk of local recurrence (LR) ≤1.5% after breast-conserving therapy (BCS) plus whole-breast radiation therapy (RT).
  
  
  METHODS
  Study subjects were 5974 patients ≥50 years of age whose cancer was diagnosed between 1989 and 2006, and were referred with pT1 pN0 invasive breast cancer treated with BCS and RT. Cases of 5- and 10-year LR were examined using Kaplan-Meier methods. Recursive partitioning analysis was performed in patients treated with and without endocrine therapy to identify combinations of factors associated with a 5-year LR risk ≤1.5%.
  
  
  RESULTS
  The median follow-up was 8.61 years. Median age was 63 years of age (range, 50 to 91). Overall 5-year LR was 1.5% (95% confidence interval [CI], 1.2%-1.9%) and 10-year LR was 3.4% (95% CI, 2.8%-4.0%). Of 2830 patients treated with endocrine therapy, patient subsets identified with 5-year LR ≤1.5% included patients with grade 1 histology (n=1038; LR, 0.2%; 95% CI, 0%-0.5%) or grade 2 histology plus ≥60 years of age (n=843; LR, 0.5%; 95% CI, 0%-1.0%). Ten-year LR for these groups were 0.8% (95% CI, 0.1%-1.6%) and 0.9% (95% CI, 0.2%-1.6%), respectively. Of 3144 patients treated without endocrine therapy, patients with grade 1 histology plus clear margins had 5-year LR ≤1.5% (n=821; LR, 0.6%; 95% CI, 0.1%-1.2%). Ten-year LR for this group was 2.2% (95% CI, 1.0%-3.4%).
  
  
  CONCLUSIONS
  Histologic grade, age, margin status, and use of endocrine therapy identified 45% of a population-based cohort of female patients over age 50 with stage I breast cancer with a 5-year LR risk ≤1.5% after BCS plus RT. Prospective study is needed to evaluate the safety of omitting RT in patients with such a low risk of LR.
authors.affiliation: Radiation Therapy Program and Breast Cancer Outcomes Unit, British Columbia Cancer Agency, Vancouver Island Centre, University of British Columbia, Victoria, British Columbia, Canada. Electronic address: ssmith11@bccancer.bc.ca.
authors.forename: Sally L
authors.initials: SL
authors.lastname: Smith
authors.affiliation: Radiation Therapy Program and Breast Cancer Outcomes Unit, British Columbia Cancer Agency, Vancouver Island Centre, University of British Columbia, Victoria, British Columbia, Canada.
authors.forename: Pauline T
authors.initials: PT
authors.lastname: Truong
authors.affiliation: Department of Mathematics and Statistics, University of Victoria, Victoria, British Columbia, Canada.
authors.forename: Linghong
authors.initials: L
authors.lastname: Lu
authors.affiliation: Department of Mathematics and Statistics, University of Victoria, Victoria, British Columbia, Canada.
authors.forename: Mary
authors.initials: M
authors.lastname: Lesperance
authors.affiliation: Division of Radiation Oncology, Tom Baker Cancer Centre, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Ivo A
authors.initials: IA
authors.lastname: Olivotto
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use; D001365:Axilla; D001943:Breast Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy / Q000601:surgery*; D016001:Confidence Intervals; D019583:Dose Fractionation, Radiation; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008197:Lymph Node Excision; D015412:Mastectomy, Segmental / Q000379:methods; D008875:Middle Aged; D015999:Multivariate Analysis; D060787:Neoplasm Grading; D009364:Neoplasm Recurrence, Local; D009367:Neoplasm Staging; D018365:Neoplasm, Residual; D016609:Neoplasms, Second Primary / Q000473:pathology; D016016:Proportional Hazards Models; D018714:Radiotherapy, Adjuvant / Q000379:methods; D012306:Risk
chemical_list: D018931:Antineoplastic Agents, Hormonal