Tam S, et al. - This study sought to assess the role of external beam radiation therapy (EBRT) in locally advanced differentiated thyroid cancer. In locally advanced differentiated thyroid cancer, particularly in patients with tracheal or esophageal invasion treated with aggressive surgical resection, the addition of EBRT to radioactive iodine (RAI) resulted in good disease control. Independent predictors of poor disease control included increased age and presence of esophageal invasion.

Methods

• From January 2000 through December 2015, for this retrospective cohort study, patients treated surgically for T4a differentiated thyroid cancer at the University of Texas MD Anderson Cancer Center were recruited.
• For analysis, 88 patients were included.
• Adjuvant treatment with RAI alone or both RAI and EBRT was provided.
• Researchers assessed disease-free survival (DFS), defined as the time from primary surgery to locoregional or distant recurrence or death due to any cause.
• They completed Kaplan-Meier survival analysis.
• With Cox proportional hazards model, univariate and multivariate analysis were completed to determine predictors of DFS.

Results

• The analysis included a total of 88 patients (44 women [50%]; mean [SD] age, 58.2 [15.3] years); median (range) follow-up period was 117 (12-164) months.
• In this study, 44 patients (50%) underwent RAI alone and 44 patients (50%) underwent RAI with adjuvant EBRT.
• EBRT was not administered to patients undergoing RAI alone owing to invasion into the recurrent laryngeal nerve only (n=14 [32%]) or invasion into the tracheal perichondrium and/or esophageal muscularis only (n=18 [41%]).
• In patients undergoing RAI alone, 5-year DFS was 43%, compared to 57% in those undergoing RAI and EBRT (effect size=14%; 95% CI, -7% to 33%).
• An increased rate of locoregional failure was observed among patients undergoing RAI alone (effect size=-32%; 95% CI, -47% to -16%); with those undergoing RAI treatment alone, for minimal tracheal perichondrium and/or esophageal muscularis invasion having worse locoregional control than those with recurrent laryngeal nerve invasion only (effect size=49%; 95% CI, 20% to 71%).
• Independent predictors of worse DFS included age (adjusted hazard ratio [adjusted HR], 1.02/y; 95% CI, 1.00 to 1.05) and esophageal invasion (adjusted HR, 2.30; 95% CI, 1.16 to 4.60).