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

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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. We aim to explore the characteristics and outcomes of 2-DTC. We retrospectively analyzed data from the SEER database (2000-2017). 2-DTC was divided into 25 subgroups based on the prior primary malignancies (PPMs). Baseline characteristics were compared using the Chi-square test. Multivariable logistic analysis was used to identified if PPMs associated with aggressive DTC characteristics. DTC-specific and cancer-specific mortality were analyzed using univariable and multivariable competing risk regression model. There were 138,555 1-DTC and 9,253 2-DTC patients were identified. 2-DTC patients were predominantly older, male, and white compared to first primary DTC (1-DTC) (all P < 0.05). In multivariable logistic regression analysis, only four types of PPMs were associated with higher rates of DTC aggressive characteristics, while 19 types exhibited lower rates (all P < 0.05). 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. 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.