Association between Waiting Time for Radiotherapy after Surgery for Early-Stage Breast Cancer and Survival Outcomes in Ontario: A Population-Based Outcomes Study

Abstract

Background: After surgery for early-stage breast cancer (bca), adjuvant radiotherapy (rt) decreases the risk of locoregional recurrence and death from bca. It is unclear whether delays to the initiation of adjuvant rt are associated with inferior survival outcomes. Methods: This population-based retrospective cohort study included a random sample of 25% of all women with stage i or ii bca treated with adjuvant rt in Ontario between 1 September 2001 and 31 August 2002, when, because of capacity issues, wait times for radiation were abnormally long. Pathology reports were manually abstracted and deterministically linked to population-level administrative databases to obtain information about recurrence and survival outcomes. Cox proportional hazards modelling was used to evaluate the association between waiting time and survival outcomes. A composite survival outcome was used to ensure that all possible measurable harms of delay would be captured. The composite outcome, event-free survival, included locoregional recurrence, development of metastatic disease, and bca-specific mortality. Results: We identified 1028 women with stage i or ii bca who were treated with breast-conserving surgery and adjuvant rt. For the 599 women who were treated with adjuvant radiation without intervening chemotherapy, a waiting time of 12 weeks or more from surgery to the start of radiation appeared to be associated with worse event-free survival after a median follow-up of 7.2 years (hazard ratio for the composite outcome: 1.44; 95% confidence interval: 0.98 to 2.11; p = 0.07). For the 429 women who received intervening adjuvant chemotherapy, a waiting time of 6 weeks or more from completion of chemotherapy to start of radiation was associated with worse event-free survival after a median follow-up of 7.4 years (hazard ratio: 1.50; 95% confidence interval: 1.00 to 2.22; p = 0.047). Conclusions: Delay to the initiation of adjuvant rt after breast-conserving surgery is associated with inferior bca survival outcomes. The good prognosis for patients with early-stage bca limits the statistical power to detect an effect of delay to rt. Given that there is no plausible advantage to delay, we agree with Mackillop that time to initiation of rt should be kept “as short as reasonably achievable.”