Racial and ethnic disparities in the risk of second primary malignancies in differentiated thyroid cancer patients: a population-based study.

[BACKGROUND] There is limited evidence on the risks of second primary malignancies (SPMs) among patients with differentiated thyroid cancer (DTC), particularly in relation to racial disparities. We aim to examine racial and ethnic disparities in the risk and temporal patterns of SPMs among DTC survivors in the U.S.

[METHODS] This retrospective cohort study, grounded in population-based data from the Surveillance, Epidemiology, and End Results (SEER) program, focused on DTC patients diagnosed between 2004 and 2015. Standardized incidence ratios (SIR) and 95% confidence intervals were employed to estimate high-risk sites for SPMs among different races. The competing risks model was applied to assess SPM risks and risk factors across racial groups, with mediation analysis conducted for selected variables.

[RESULTS] Among 90,186 DTC patients, 8.3% developed SPMs. DTC survivors face a 15% higher risk of developing SPMs compared to the general population. Blacks demonstrated a significantly lower risk of SPMs, while other ethnic groups faced higher risks than Whites. Specific SPM risk factors for Whites, Blacks, and other ethnicities were receiving radiotherapy, diagnosis at a distant stage, and tumors exceeding 40 mm, respectively. Specifically, Blacks and other ethnic groups primarily encounter SPMs in the salivary glands, soft tissues, hematologic, and urinary systems, often earlier than in Whites. Conversely, Whites had a broader distribution of risk sites, with a notable risk for other endocrine tumors, manifesting 48-87 months post-diagnosis.

[CONCLUSIONS] DTC patients show significant racial and ethnic disparities in high-risk sites, temporal patterns, SPM risks and risk factors. Personalized follow-up for diverse ethnic backgrounds can ameliorate disparities, enhancing SPM risk and survival outcomes.