Study Links Radioactive Iodine Therapy to Increased Melanoma Risk

A new study found elevated risk of melanoma and other nonkeratinocyte skin cancers in patients with primary thyroid cancer who received radioactive iodine therapy, particularly in the head and neck region.

In the JAMA Network Open article “Development of Melanoma and Other Nonkeratinocyte Skin Cancers After Thyroid Cancer Radiation,” Stanford University researchers employed US population-based data from 17 cancer registries made available through the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute; they included patients with thyroid cancer diagnosed from 2000 to 2019 and followed up through 2020 for subsequent cancers.

Of the 174,916 patients with primary thyroid cancer diagnosed from 2000 to 2019, 79,576 (45.5%) had first-course treatment of some form of radiation. A total of 865 nonkeratinocyte skin cancers (790 melanoma) were diagnosed following thyroid cancer, and, of those, 171 (19.8%) were located on the skin of the head or neck. When limiting the cancer site to the head and neck skin, the standardized incidence ratios (SIRs) were higher than expected following thyroid cancer treated with radioactive iodine for all nonkeratinocyte skin cancers (SIR, 1.64; 95% cancer incidence [CI], 1.32-2.02), melanoma (SIR, 1.56; 95% CI, 1.22-1.97) and other nonkeratinocyte skin cancers (SIR, 2.07; 95% CI, 1.23-3.27). The risk of head and neck skin cancer was not elevated in patients who did not receive radioactive iodine therapy. The SIR was statistically significant if the primary thyroid cancer treated with any type of radiation was the papillary subtype (SIR, 1.69; 95% CI, 1.35-2.09) but not for other thyroid cancer subtypes, which the authors said was likely due to insufficient sample sizes of other subtypes.

“Although the risks of subsequent cancer do not outweigh the benefits of treatment, our findings suggest that patients treated for thyroid cancer may benefit from follow-up skin cancer screening,” the authors wrote.