Locally Advanced, pT4 Well-Differentiated Thyroid Cancer in Young Patients – A Population-Based Study

Abstract

<h3>Purpose/Objective(s)</h3> Locally advanced, non-metastatic pT4 well-differentiated thyroid cancer (WDTC) diagnosed at age <55 years is considered to be Stage I disease by the American Joint Committee on Cancer (AJCC) 8^th edition staging system implying excellent cause-specific survival (CSS) outcomes of ≥95% at 10 years. There are no published outcomes however on this specific cohort of patients, and they may be underrepresented in published outcome series as they comprise of <5% of all WDTC patients. Thus, the objective was to determine the recurrence and survival outcomes of this cohort. <h3>Materials/Methods</h3> We conducted a population-based retrospective study of all patients with pT4 WDTC diagnosed at age <55 years, treated in our province from 1985 to 2013 were extracted. Demographic and treatment factors were extracted. The primary endpoints were cumulative incidence of locoregional recurrence (LRR), cause-specific survival (CSS) and overall survival (OS). Competing risk Fine-Grays analysis and Cox-proportional hazards model was used. <h3>Results</h3> There were 218 patients (median follow up 18.2 years) with 137 under the age of 45. Patients were all treated with thyroidectomy. Most patients had papillary histology (95.9%). Adjuvant radioactive iodine was administered in 88% of cases, and 43% received adjuvant external-beam radiotherapy (EBRT). The 15-year LRR was 21%. On multivariate analysis, there was a trend towards EBRT receipt and lower LRR (HR:0.47, p=0.06). Of the patients who did not receive EBRT, but had a LRR (n=19), 11 were salvaged (with RAI, EBRT, and surgery) and only two died of WDTC (both from LRR). For the cohort as a whole, the 15-year CSS was 96%. There were four deaths secondary to LRR and seven deaths from distant disease. Advanced age, larger tumor size, higher T stage, and presence of LVI were associated with worse CSS (all p<0.05), though we note the limited number of events limit the conclusions from our multivariate analysis. The 15-year OS was 93%. Older age, tumor size, and lymphovascular invasion were significantly associated with worse OS (all p<0.05). On multivariate analysis, EBRT receipt was not associated with improved CSS or OS. <h3>Conclusion</h3> Despite very locally advanced disease, patients with non-metastatic pT4 WDTC, <55 years at diagnosis, have favorable long-term outcomes. Further prospective studies of adjuvant EBRT are needed in this population.