Risk and outcome of subsequent malignancies after radioactive iodine treatment in differentiated thyroid cancer patients.

BACKGROUND

We identified differentiated thyroid cancer (DTC) survivors from SEER registries and performed Poisson regression to calculate the relative risks (RRs) of subsequent malignancies (SMs) by different sites associated with radioactive iodine (RAI) treatment, and the attributable risk proportion of RAI for developing different SMs.

RESULTS

We identified 4628 of 104,026 DTC patients developing a SM after two years of their DTC diagnosis, with a medium follow-up time of 113 months. The adjusted RRs of developing SM associated with RAI varied from 0.98 (0.58-1.65) for neurologic SMs to 1.37 (1.13-1.66) for hematologic SMs. The RRs of developing all cancer combined SMs generally increased with age at DTC diagnosis and decreased with the latency time. We estimated that the attributable risk proportion of RAI treatment is only 0.9% for all cancer combined SMs and 20% for hematologic SMs, which is the highest among all SMs. The tumor features and mortalities in patients treated with and without RAI are generally comparable.

CONCLUSION

With the large population based analyses, we concluded that a low percentage of DTC survivors would develop SMs during their follow-up. Although the adjusted RR of SMs development increased slightly in patients receiving RAI, the attributable risk proportion associated with RAI was low, suggesting the absolute number of SMs induced by RAI in DTC survivors would be low. The attributable risk proportion of RAI treatment is the highest in hematological SMs, but when in consideration of its low incidence among all DTC survivors, the absolute number of hematological SMs was low.