2341 - Real-World Data of Radiotherapy Induced Hypothyroidism in Head and Neck Cancer Patients

Purpose/Objective(s): Hypothyroidism is a common toxicity experienced after radiotherapy (RT) for head and neck malignancies. This study investigates its incidence, risk factors, and impact on survival using real-world data.

Materials/Methods: This study analyzed data from the TriNetX Research Database, focusing on patients over 20 years old diagnosed with head and neck cancer. Exclusions included a past history of hypothyroidism, thyroid cancer, thyroidectomy, or hypothyroidism due to other causes. From over 143 million medical records (2005–2024), 356,964 patients met the criteria. There were 213,032 males (69.0%), 90,613 females (29.36%), and 5,025 unspecified gender (1.63%). Race distribution was 54.0% White, 10.6% Asian, 7.3% Black, and 28.1% other races. Patients were stratified by whether they received RT (n = 72,452) or did not (n = 284,512) after their cancer diagnosis. Propensity score matching was conducted to balance baseline characteristics, including age, gender, race, primary tumor site, tumor stage, surgical history, and the use of antineoplastic medications. After matching, each cohort contained 46,407 patients. Hypothyroidism was defined by at least one of the following criteria occurring after the diagnosis of head and neck cancer: a documented history of hypothyroidism, prescription of levothyroxine, a thyroglobulin level of = 4500 ng/dL, or a thyrotropin (TSH) level of = 4.5 mIU/L. The incidence of hypothyroidism was compared between groups using the Chi-square test, while the Kaplan-Meier method assessed cumulative incidence over time. Risk factors for RT induced hypothyroidism were also analyzed. Finally, progression-free survival (PFS) and overall survival (OS) were compared between RT-treated patients with or without hypothyroidism using the Kaplan-Meier method.

Results: After a median follow-up of 20.6 months, hypothyroidism was observed in 4,818 (10.9%) patients who received RT and 2,634 (6.1%) who did not (p < 0.0001). The Risk factors for hypothyroidism following RT included older age at diagnosis (p < 0.0001), White race (p < 0.0001), tumor location in the oropharynx, hypopharynx, or larynx (p < 0.0001), and the use of antineoplastic medications (p < 0.0001). The hazard ratio (HR) of hypothyroidism for PFS and OS was 0.80 (95% CI: 0.72 - 0.90) and 0.79 (95% CI: 0.74 - 0.84), respectively.

Conclusion: Hypothyroidism occurred in 10.9% of RT treated patients and was associated with older age, White race, specific tumor sites, and antineoplastic use. Notably, hypothyroidism correlated with improved PFS and OS.