TUMOR SIZE IS AN INDEPENDENT PREDICTOR OF MORTALITY RISK IN DIFFERENTIATED THYROID CANCER PATIENTS WITH T4 DISEASE.

Objective: The eighth edition of the American Joint Committee on Cancer (AJCC) guideline on the tumor-node-metastasis staging system has been applied in clinical practice for thyroid cancer since 2018. However, using these criteria, a few studies have shown no significant difference between stage III and IV diseases amongst the differentiated thyroid cancer (DTC) patients. Thus, we aimed to study the underlying reason behind this observation. Methods: Patients were selected from the Surveillance, Epidemiology, and End Results database between 2004 and 2015. The Cox proportional hazards regression model was used for the univariate and multivariate analyses to plot the Kaplan-Meier survival curves for overall survival (OS) and disease-specific survival (DSS). Results: A total of 1,431 patients had a median tumor size of 3.0 cm (range: 0.1 to 50 cm). When stratified by tumor size (<= 2cm, 2 to 4 cm, and >4 cm), lower survival rates were observed in patients with stage III (T4a) cancer and large tumor size than in those with stage IVA (T4b) cancer and small tumor size. Univariate and multivariate analyses showed that tumor size (<= 4 cm versus >4 cm) is an independent prognostic factor for OS (P<.001) and DSS (P<.001) in DTC patients with T4a and T4b diseases. Conclusion: Tumor size is an independent prognostic factor for OS and DSS in DTC patients with T4 disease; tumor size-related modification of the T4 category can improve the AJCC staging system for DTC patient with stage III-IV diseases.