ATA: Pediatric Radioactive Iodine Therapy for Thyroid Ca Increases Second Malignancy Risk

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(ChemotherapyAdvisor) – Children and young adults treated with radioactive iodine for differentiated thyroid cancer are at increased risk of developing a second primary malignancy, mainly salivary gland cancer, results of a study reported at the 82nd Annual Meeting of the American Thyroid Association (ATA) in Québec City, Québec, Canada, September 20 has found.

Over a decade, 1 in 227 patients with differentiated thyroid cancer treated with radioactive iodine will develop a second primary malignancy and 1 in 588, a salivary cancer attributable to the treatment, according to excess absolute risk estimates reported by Jennifer Marti, MD, of Beth Israel Medical Center in New York.

“Because the expected survival time for young differentiated thyroid cancer patients is long, it is critical to carefully weigh the benefits of radioactive iodine against the small, but real, increase in the second primary malignancy risk,” she reported.

Dr. Marti and colleagues analyzed 3,850 patients ages 25 years or younger with differentiated thyroid cancer followed in the National Cancer Institute's Surveillance Epidemiology and End Results (SEER) cancer registry from 1973-2008, a group that equated to 38,605 person-years at risk.

Excess risk was compared in patients both treated (1571, or 40% of the total) and not treated with radioactive iodine.

“The percentage of patients treated with radioactive iodine increased over time, from 4% in 1973 to 62% in 2008 (P<0.001),” Dr. Marti stated. “Among patients who received radioactive iodine, 26 second primary malignancies were observed, and 18.3 were expected.” Relative risk of a second primary malignancy at any site was 1.42 (P=0.05), or 4.4 excess cases per 10,000 person-years at risk, a finding not observed in the nontreated patients.

Those treated with radioactive iodine also had a “dramatically elevated risk” for a salivary malignancy (SIR 34.12, P<0.001), 1.7 excess cases per 10,000 person-years at risk. Leukemia risk was also elevated (SIR 3.98) but was not statistically significant (P=0.31). No elevated risk of salivary cancer or leukemia was observed in the patients not treated with radioactive iodine.

Abstract [Click on Full Text PDF and search using author name Marti]

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