J. M. Lee1, R. Cress1, Y. Chen1, W. T. Shen2, M. J. Campbell1 1University Of California – Davis,Sacramento, CA, USA 2University Of California – San Francisco,San Francisco, CA, USA
Introduction: The role of external beam radiation therapy (EBRT) in patients with differentiated thyroid cancer remains ill defined. Previous studies have suggested that some patients with locally advanced cancers and those > 60 years of age may have improved outcomes with EBRT.
Methods: We used the California Cancer Registry (CCR) to evaluate the influence of EBRT on survival in patients with T4 differentiated thyroid cancer. The overall and cause-specific survival were estimated using a Kaplan-Meier method and the unadjusted differences compared using a log-rank test. Cox proportional-hazard models were used to evaluate the effect of EBRT in predefined subgroups.
Results: We identified 1664 patients who underwent a thyroidectomy for a T4 differentiated thyroid cancer. 134 patients received EBRT. Patients who received EBRT had a worse disease specific survival (61% vs 93%, p<0.001) and overall survival (47% vs 79%, p<0.001) when compared to patients who did not receive EBRT. In a subgroup analysis, receiving EBRT increased the risk of death regardless of age (<60 years old [HR = 8.7, CI = 4.5 – 16.9], >60 years old [HR = 6.0, CI = 3.8 – 9.5]), gender (women [HR = 6.7, CI = 4.0 – 11.1], men [HR = 7.0, CI = 3.9 – 12.5]), tumor size (<4cm [HR = 6.4, CI = 3.5 – 11.7], >4cm (HR = 6.4, CI 3.9 – 10.5]), or M-stage (M0 [HR = 7.6, CI = 4.7 – 12.3], M1 [HR = 3.6, CI = 1.8 – 6.9]). No histologic subtype showed an improved survival after receiving EBRT (follicular cancer HR = 11.3, CI = 3.5 – 36.9, papillary cancer HR = 6.6, CI = 4.6– 10.7, mixed follicular and papillary HR = 6.7, CI = 2.4 – 18.6).
Conclusion: Although often reserved for select patients with a poor prognosis, EBRT does not appear to improve survival in patients with locally advanced thyroid cancer regardless of their age, gender, tumor size, M-stage, or histologic subtype.