2.2. Data Collection

All centers collected core data elements related to thyroid cancer diagnosis and treatment. The core data elements collected related to presentation of thyroid cancer, including year of diagnosis, age at diagnosis, sex, initial surgical management, pathology, staging, and RAI administration.

Individual cases of thyroid cancer were staged according to the American Joint Committee on Cancer (AJCC) tumor-node-metastasis (TNM) classification system (7th edition, 2009). All patients were retrospectively reclassified based on the clinical information collected in the database. Information pertaining to clinical and pathological stage of thyroid cancer at presentation was obtained from clinic notes prepared by treating physicians and cross-referenced with original pathology and/or imaging reports. All data was deidentified to protect patients' privacy and confidentiality and submitted for central data analysis. The data has been carefully verified, and we checked for potential duplicates to avoid including the same patient more than once.