Patterns of adjuvant care and outcomes of elderly women with stage I breast cancer after breast-conserving surgery: a population-based analysis
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Randomized trials studying endocrine therapy (ET) with and without radiation therapy (RT) following breast-conserving surgery (BCS) have detected differences in local recurrence (LR) but not survival among elderly women with hormone receptor positive stage I breast cancer (BC). We assembled a population-based cohort of such women to examine the use and outcomes associated with or without the administration of adjuvant radiotherapy (RT) or ET.
Women aged ≥ 65 years with stage I BC treated with BCS in Ontario between 2010 and 2016, their treatments and outcomes were ascertained using deterministic linkages of administrative databases. Multivariable Cox regression models were used to evaluate risks of ipsilateral LR and of any first in-breast event, categorizing women by their treatment.
5076 women were treated with BCS followed by RT + ET (n = 1964), RT alone (n = 1325), ET alone (n = 719), or no adjuvant treatment (n = 1068). Median follow-up was 5 years. LR occurred in 0.9% after adjuvant RT + ET, 1.4% after RT alone, 3.1% after ET alone, and 9.4% after BCS alone (p < 0.001). The adjusted risk of LR was increased in those who received no adjuvant therapy (HR = 13.43, CI: 7.89, 22.85), or ET alone (HR = 4.03, CI: 2.14, 7.59). The adjusted risk of any first in-breast event was greatest among those without any adjuvant therapy (HR = 7.61, 95%CI: 5.21, 11.11, p < 0.0001). Absolute and adjusted risks of any first in-breast event were comparable between those with ET alone (HR = 2.09, 95%CI: 1.27, 3.43, p = 0.0038) and those with RT alone (HR = 1.91, 95% CI: 1.25, 2.91, p = 0.0028).
Older women with stage I BC who receive no adjuvant therapy have a significant absolute risk of LR and any first in-breast event, whereas the absolute risk of these events among those with either RT alone or ET alone is only slightly higher than among those treated with both.
KeywordsBreast cancer Elderly Population-based Local recurrence Radiotherapy Patterns of care
This study was supported by the ICES, which is funded by an annual grant from the Ontario Ministry of Health and Long-Term Care (MOHLTC). The opinions, results, and conclusions reported in this paper are those of the authors and are independent from the funding sources. No endorsement by ICES or the Ontario MOHLTC is intended or should be inferred. These datasets were linked using unique encoded identifiers and analyzed at the ICES. Parts of this material are based on data and/or information compiled and provided by CIHI. However, the analyses, conclusions, opinions, and statements expressed in the material are those of the author(s), and not necessarily those of CIHI. Parts of this material are based on data and information provided by Cancer Care Ontario (CCO). The opinions, results, view, and conclusions reported in this paper are those of the authors and do not necessarily reflect those of CCO. No endorsement by CCO is intended or should be inferred. We thank IMS Brogan Inc. for use of their Drug Information Database.
E Rakovitch has received research grant funding from Genomic Health Inc. T Whelan has received research grant funding outside of this work from Genomic Health Inc.
Compliance with ethical standards
Conflict of interest
All other authors declare no conflict of interest.
This study was approved by the Sunnybrook Health Sciences Centre Research Ethics Board. It is an observational analysis, and no procedures or interventions were performed.
This is a population-based retrospective analysis. All personal identifiers for each case in this population cohort were removed. This study was facilitated through ICES which is named as a prescribed entity in Section 45 of PHIPA (Regulation 329/04, Section 18), which allows access and utilization of administrative data for research purposes with a waived requirement for consent.
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