This study aims to thoroughly examine survival disparities in patients with T3 or T4 stage follicular thyroid carcinoma (FTC) as classified by the AJCC staging system. It compares outcomes between those who underwent total thyroidectomy (TT) and those who did not, and assesses the influence of radioactive iodine therapy (RAIT) on the survival of patients without TT. Utilizing the SEER database, a retrospective study identified patients diagnosed with T3 or T4 FTC, categorizing them into two cohorts: those treated with TT and those who were not (No-TT). The No-TT group was further analyzed to determine the impact of RAIT on patient survival. Propensity score matching (PSM) was applied to adjust for confounding variables. Survival analysis, including Kaplan-Meier survival curves and Landmark analysis, was conducted to evaluate the effects of surgical intervention and RAIT on overall survival (OS) and cancer-specific survival (CSS).

Inclusion Criteria:1.The primary site code C73.9, denoting the thyroid gland;2.The International Classification of Diseases for Oncology, Third Edition (ICD-O-3) histology types comprising 8330 (Follicular adenocarcinoma, NOS), 8331 (Follicular adenocarcinoma well differentiated), 8332 (Follicular adenocarcinoma trabecular), 8335 (Follicular carcinoma, minimally invasive), and 8339 (Follicular thyroid carcinoma (FTC), encapsulated angioinvasive).

Exclusion Criteria:(1). Absence of T stage information or designation as T1, T2; (2). Missing surgery codes; (3). Cases not verified by histopathological analysis; (4). FTC not being the initial malignancy diagnosed in the patient; (5). Unknown survival duration or survival less than one month; (6). Presence of bilateral tumors.

The SEER database was established in 1973, serves as a public database and research resource developed by the National Cancer Institute (NCI) of the United States. It encompasses data covering approximately 30% of the U.S. population. The dataset for this retrospective study was obtained from the SEER Research Data, encompassing information from 17 registries as of November 2022, which includes cases recorded between the years 2000 and 2020.

De-identified individual participant data (IPD) will be shared with researchers upon reasonable request.

Data will be available beginning 6 months after publication of the main study results and will be accessible for a period of 5 years.

Researchers seeking access to the IPD must submit a methodologically sound proposal. Requests should be directed to the principal investigator and will be evaluated on the basis of scientific merit and ethical considerations.