External beam radiotherapy in pT4 well-differentiated thyroid cancer: A population-based study of 405 patients.

Abstract Purpose/Objective The benefit of external beam radiotherapy (EBRT) in locally advanced, well- differentiated thyroid cancer (WDTC) is uncertain. The purpose of this study is to evaluate locoregional recurrence (LRR), progression-free survival (PFS) and cause-specific survival (CSS) of patients with pT4 well-differentiated thyroid carcinoma. Materials/Methods A population-based retrospective review was conducted of consecutive patients with pT4 (American Joint Committee on Cancer 8th edition) WDTC treated provincially between 1985 to 2013. The primary end points were cumulative incidence of locoregional recurrence (LRR) and cause-specific survival (CSS). To account for the competing risks of death from other causes, Fine-Gray's test was used. Cox-proportional hazards model was used for analyzing overall survival (OS). Multivariate models and propensity matching was used to account for the effects of covariates. Results A total of 405 patients were identified with a median follow up time of 14.3 years for a total of 4209 person-years of follow up. The median age at diagnosis was 53 years (range: 20-87). There were 211 patients (52%) who received EBRT. EBRT receipt was associated with age ≥55 (56% vs 35%, p Conclusion In this large, population-based analysis of patients with pT4 WDTC, EBRT was associated with lower rates of LRR, but no difference in CSS or OS.