Risk of second primary malignancy after radioiodine for thyroid carcinoma: a SEER-based study

Abstract Purpose The objective of this study is to evaluate the benefits of radioactive iodine (RAI) treatment and the risk of second primary malignant (SPM) in RAI treated patients. Methods The cohort for this analysis consisted of individuals diagnosed with a first primary differentiated thyroid carcinoma (DTC), reported by SEER database in 1988–2016. Overall survival (OS) difference was estimated by Kaplan–Meier curves and Log-Rank test, and hazard ratios (HR) was obtained by cox proportional hazard model to evaluate the association between RAI and SPM. Standardized incidence ratios (SIR) were calculated to assess cancer incidence in relation to RAI and no-RAI groups and the general population. Results Among 130,902 patients, 61,210 received RAI and 69,692 did not and a total of 8,604 patients developed SPM. We found that OS was significantly higher in patients who received RAI than those who did not (P < 0.001). DTC survivors treated with RAI had increased risk of SPM in females (6.27% versus 5.97%, P = 0.043), particularly for SPM occurred in ovary (RAI group: 0.17%, no-RAI group: 0.12%, P = 0.039) and leukemia (RAI group: 0.22%, no-RAI group: 0.12%, P < 0.0001). In addition, RAI group in all age subgroups demonstrated higher SPM incidence than no-RAI group, and the incidence increased with age. Patients with primary thyroid cancer had a 16% elevated risk of developing SPM in all sites (SIR:1.16), 243% elevated risk in salivary glands (SIR:3.43), 119% elevated risk in kidneys (SIR:2.19), and 46% elevated risk in hematopoietic System (SIR:1.46). In general, the risk of developing SPM was higher in RAI group than in no-RAI group and general population. Conclusions Increased risks of SPM occur in female DTC survivors treated with RAI, which become more obvious with age increasing. Our research findings were beneficial to the formulation of radioactive iodine treatment strategies and the prevention of secondary tumors for patients with thyroid cancer of different genders and different ages.