In a study reported in the Journal of Clinical Oncology, Molenaar et al found that radioiodine treatment for well-differentiated thyroid cancer was associated with an increased risk of acute myeloid leukemia (AML) and chronic myeloid leukemia (CML) compared with thyroidectomy alone.
The study involved data from the April 2017 release of all 18 registries of the SEER (Surveillance, Epidemiology, and End Results) program on 148,215 patients with well-differentiated thyroid cancer. Of these, 53% received surgery alone and 47% received radioactive iodine treatment.
Risk of AML, CML
Overall, 783 patients developed a second hematologic malignancy after median follow-up of 6.5 years. The estimated cumulative risk of any second hematologic malignancy over the first 10 years was 0.40% after surgery alone vs 0.54% after surgery plus radioiodine treatment; cumulative risks of AML and CML were 0.08% and 0.01% vs 0.12% and 0.06%.
In multivariable analysis, surgery plus radioiodine treatment was associated with increased risk of developing any second hematologic malignancy (hazard ratio [HR] = 1.43, P < .001); increased risk was significant for AML (HR = 1.79, P = .01) and CML (HR = 3.44, P < .001) but not for other second hematologic malignancies. Increased risk of AML and CML after radioiodine treatment was observed among all tumor risk levels.
Regardless of the treatment received, occurrence of AML but not CML was associated with poorer overall survival compared with matched patients with well-differentiated thyroid cancer who did not develop AML (median = 8.0 vs 31.0 years, P = .001). Median overall survival was nonsignificantly shorter for AML after radioiodine treatment vs surgery alone (6.7 vs 9.4 years, P = .12). There was a trend toward poorer survival with AML developing after radioiodine therapy vs de novo AML in matched controls (median = 1.2 vs 2.9 years, P = .06).
The investigators concluded, “Patients with [well-differentiated thyroid cancer] treated with [radioiodine] had an increased early risk of developing AML and CML but no other hematologic malignancies. AML that arises after [radioiodine] treatment has a poor prognosis. [Radioiodine] use in patients with [well-differentiated thyroid cancer] should be limited to patients with high-risk disease features, and patients with [well-differentiated thyroid cancer] treated with adjuvant [radioiodine] should be monitored for myeloid malignancies as part of cancer surveillance.”
The study was supported by the American Cancer Society.
Sudipto Mukherjee, MD, PhD, MPH, of the Taussig Cancer Institute, Cleveland Clinic, is the corresponding author for the Journal of Clinical Oncology article.
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