Second Primary Differentiated Thyroid Carcinoma in Adult Cancer Survivors: A SEER Database Analysis

Context: Adult cancer survivors are at a heightened risk for secondary primary differentiated thyroid carcinoma (2-DTC). The characteristics and outcomes of 2-DTC remain poorly understood. Objective: We aimed to explore the characteristics and outcomes of 2-DTC. Methods: We retrospectively analyzed data from the Surveillance, Epidemiology, and End Results (SEER) database (2000-2017). 2-DTC was divided into 25 subgroups based on prior primary malignancies (PPMs). Baseline characteristics were compared using the chi-square test. Multivariable logistic analysis was used to identified if PPMs were associated with aggressive DTC characteristics. DTC-specific and cancer-specific mortality were analyzed using a univariable and multivariable competing risk regression model. Results: There were 138 555 1-DTC and 9253 2-DTC patients identified. 2-DTC patients were predominantly older, male, and White compared to first primary DTC (1-DTC) (all P < .05). In multivariable logistic regression analysis, only 4 types of PPMs were associated with higher rates of DTC aggressive characteristics, while 19 types exhibited lower rates (all P < .05). In multivariable competing risk analysis, 2-DTC showed no mortality risk in stages I (SHR: 1.16; 95% CI, 0.65-2.07) and II (SHR: 0.67; 95% CI, 0.45-1.01), but a protective role in stages III (SHR: 0.47; 95% CI, 0.27-0.83) and IV (SHR: 0.72; 95% CI, 0.52-0.99). Most PPMs that developed into 2-DTC had a lower risk of DTC-specific death than 1-DTC, but many PPMs had a higher risk of cancer-specific death. Conclusion: Given the characteristics and outcomes of 2-DTC, aggressive treatment for 2-DTC, particularly for PPM with a high mortality risk, may not be advisable.