Using radioactive iodine as a follow-up treatment to thyroid cancer surgery increases the risk of a patient developing acute myeloid leukemia and having a poorer outcome, a study reports.
Researchers presented the findings at the Congress of the European Society for Medical Oncology in Madrid, Sept. 8-12. The presentation was titled “Risk of developing acute myeloid leukemia (AML) in well-differentiated thyroid cancer (WDTC) patients treated with radioactive iodine (RAI): a population-based study.”
Studies have shown that the risk of a patient with another cancer developing acute myeloid leukemia, or AML, increases after radiation.
Researchers decided to study cases of well-differentiated thyroid cancer, or WDTC, that doctors had treated either with surgery or with surgery followed by radioactive iodine. The team looked at cases in a U.S. cancer database known as Surveillance Epidemiology and End Results, or SEER.
They found 148,215 patients with WDTC diagnosed between 1973 and 2014. Fifty-five percent had had surgery alone and 45 percent surgery plus radioactive iodine, or RAI.
Forty-four patients developed acute myloid leukemia after surgery, compared with 56 who received surgery plus radioactive iodine. After adjusting for age, sex, and year of thyroid cancer diagnosis, researchers discovered that patients who had both surgery and RAI were 5.6 times more likely to develop AML than the general population, where AML occurs at a lower rate. The risk peaked in the first three years after treatment with RAI.
In addition to radioactive iodine treatment, tumor stage and patients’ age were predictors of acute myeloid leukemia.
Another finding was that the prognosis was worse for the thyroid cancer patients who developed AML after radioactive iodine therapy than for those who developed AML spontaneously. Patients treated with RAI survived a median of 1.2 years, compared with 3.5 years for those who developed AML spontaneously.
In addition, thyroid cancer patients who had surgery plus RAI, then developed AML, did not survive nearly as long thyroid cancer patients who were successfully treated and did not develop AML.
“RAI treatment is associated with an increased risk of developing AML in WDTC survivors,” the researchers wrote. “RAI-related AML has a poor survival, similarly to t-AML that arises after radiotherapy or chemotherapy. Considering young patient ages at WDTC diagnosis and high survival rates, the rates of AML in WDTC survivors are likely to continue to rise.”