Radioactive iodine (RAI) therapy may increase the risk of acute myeloid leukemia (AML) and chronic myeloid leukemia (CML) among patients with well-differentiated thyroid cancer (WDTC), according to a study published in the Journal of Clinical Oncology.1

Although RAI improves overall survival (OS) and disease-free survival (DFS) among patients with advanced WDTC, the clinical benefit for low- and intermediate-risk tumors is uncertain. Some studies suggest that RAI increases the risk of second hematologic malignances (SHM).

For this study, investigators accessed the Surveillance, Epidemiology, and End Results (SEER) database and identified 148,215 patients diagnosed with follicular or papillary WDTC and SHM. Researchers performed risk aggression analyses to calculate the SHM risk after WDTC treatment.

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More than half (79,033; 53%) of evaluated patients received surgery alone and 68,374 (47%) patients received surgery plus RAI. Of the 783 patients who developed an SHM within a median of 6.5 years after WDTC diagnosis, 417 and 366 patients received surgery vs surgery plus RAI, respectively.

Patients who underwent surgery plus RAI were at a higher early risk of developing an SHM vs surgery alone (hazard ratio [HR], 1.43; 95% CI, 1.20-1.69; P < .001). The risk was significantly elevated for AML (HR, 1.79; 95% CI, 1.13-2.82; P = .01) and CML (HR, 3.44; 95% CI, 1.87-6.36; P < .001).

This effect was observed not only for high-risk WDTC tumors, but also for low- and intermediate-risk tumors.

The risk of SHM development increased early after treatment: the risk of AML peaked in the second year after RAI treatment (risk ratio [RR], 7.1; 95% CI, 4.3-11.2; P < .001), as did the risk for CML (RR for years 2 to 10, 6.3; 95% CI, 4.4-8.8; P < .001).

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The risk of AML decreased after 2 years, returning to baseline within 6 years of WDTC diagnosis, but the risk of CML remained elevated for up to 10 years.

Patients who developed AML had a shorter median OS of 8.0 years compared with 31.0 years for CML (P = .001), and patients with AML attributed to RAI had insignificantly worse survival outcomes compared with patients with de novo AML (1.2 years vs 2.9 years; P = .06).


  1. Molenaar RJ, Sidana S, Radivoyevitch T, et al. Risk of hematologic malignancies after radioiodine treatment of well-differentiated thyroid cancer. J Clin Oncol. 2017 Dec 18. doi: 10.1200/JOC.2017.75.0232 [Epub head of print]