Background and aims
Compared to the general population, the incidence of thyroid cancer in childhood and adolescent and young adult malignancy survivors is increased 14.0–18.0 times (CI 11.7–23.8). The cumulative incidence is variably reported as 0.5% by age 45 with 30-year incidence of 1.3% in women and 0.6% in men. This study aims to evaluate the incidence of radiation-associated thyroid cancer amongst patients treated with prior radiation to the thyroid followed up in a late effects service. A secondary aim was to assess screening compliance in this cohort.
The medical records of all patients attending the late effects service from 1 January 2000 to 20 February 2013 were interrogated to identify patients exposed to thyroid irradiation. The screening compliance and incidence of thyroid cancer were assessed for the duration whilst under the guidance of the late effect service. Mode of diagnosis, all imaging and cytology were retrieved from the institutional electronic record. Cytology was categorized according to Bethesda.
Four hundred and sixty-five patients were exposed to direct or scatter neck irradiation. Compliance with thyroid surveillance was observed in 76.9%. Ultrasound features of microcalcification and increased internal vascularity had a low sensitivity (62.5%) for predicting a malignant nodule, which improved when used in conjunction with a Bethesda IV–VI result (91.7%). However, cytological assessment was not performed in 45.6% of operative cases. Thirty-three patients had thyroid carcinoma of which 45.4% (n = 15) were incidental. The majority were papillary thyroid cancers (88.9%); of which 12.5% were node positive and 34.4% were multifocal. The incidence of thyroid cancer was elevated 57.6 times compared to the Australian general population (p < 0.001).
Due to the high incidence of thyroid cancer, this study supports screening in this cohort. However, due to the risk of overtreatment, we endorse further investigation of thyroid nodules with ultrasound-guided fine-needle aspiration cytology based on sonographic criteria as for the general population and American Thyroid Association guidelines.