Second Primary Papillary Thyroid Carcinoma: Insights From Competing Risk Analysis and Post‐RAIT

Background Improved cancer survival rates have highlighted second primary malignancies (SPMs), with the thyroid gland being one of the most common organs developing SPMs in cancer survivors. Second primary papillary thyroid carcinoma (2‐PTC) is the predominant type, yet it remains poorly understood. This study aims to delineate the clinicopathological features and survival outcomes of 2‐PTC and assess the efficacy of postoperative radioactive iodine therapy (post‐RAIT) in reducing mortality risks in intermediate‐risk 2‐PTC patients. Methods Using the SEER‐17 database (2004–2019), we identified 6399 2‐PTC patients as Cohort 1 to analyze characteristics and outcomes, and 1743 as Cohort 2 to examine post‐RAIT effects. Competing risk regression models were applied to assess mortality risks from prior primary malignancies (PPMs) and other causes. Propensity score matching and stabilized inverse probability treatment weighting with 500 bootstrap samples were used for robust analysis. Results Predominant demographic characteristics of 2‐PTC patients included older age, female sex, and white ethnicity. Breast (25.5%), prostate (9.8%), and skin cancer (6.7%) were the most common PPMs. Unfavorable PPMs were found in 6.3% of patients. Despite lower cumulative mortality from 2‐PTC compared to PPMs and other causes, post‐RAIT did not significantly reduce mortality risks in Cohort 2, even among patients aged ≥ 55 years, with clinical stage IV disease, or unfavorable PPMs. Sensitivity analyses confirmed these findings. Conclusion The survival prognosis for 2‐PTC patients is generally favorable, and post‐RAIT does not significantly affect mortality in intermediate‐risk cases, indicating a need for reevaluation of its use.