Risk of Second Primary Malignancies After External Beam Radiotherapy for Thyroid Cancer

To investigate the association between external beam radiotherapy (EBRT) and the incidence of second primary tumors in patients with thyroid cancer.

Data were extracted from the Surveillance, Epidemiology, and End Results 9 database. The study cohort included patients diagnosed with thyroid cancer between 1973 and 2017. Risk factors for second primary malignancies were identified with Cox proportional hazards models. Propensity score-matched analyses were used to assess the association between EBRT and second primary malignancies.

Out of 72,392 patients with thyroid cancer, 7,684 (10.6%) developed a subsequent primary malignancy. Propensity score-matched analysis demonstrated patients receiving EBRT were more likely to develop second primary malignancies [30-year cumulative incidence=35.3% (95% confidence interval (CI)=30.4-39.8% vs. 28.1% (95% CI=27.0-29.2%); hazard ratio=1.17 (95% CI=1.03-1.33)].

In patients with thyroid cancer, EBRT is associated with an increased incidence of second primary malignancies.