Patients with thyroid cancer who receive radioactive iodine therapy may have a higher risk of developing melanoma and other nonkeratinocyte skin cancers, particularly in the head and neck region, according to a recent letter.

In the letter, published in JAMA Network Open, investigators evaluated the risk of melanoma and nonkeratinocyte skin cancers in patients with primary thyroid cancer treated with radioactive iodine therapy. Using data from 17 U.S. cancer registries in the Surveillance, Epidemiology, and End Results (SEER) Program, the investigators followed 174,916 patients diagnosed with thyroid cancer from 2000 to 2019, of whom 45.5% received radiation as part of their initial treatment.

Patients who underwent radioactive iodine therapy had a greater likelihood of developing melanoma and other nonkeratinocyte skin cancers, with a particularly increased risk when the cancers were located on the head and neck. Standardized incidence ratios (SIR) were elevated for all nonkeratinocyte skin cancers (SIR = 1.64, 95% confidence interval [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 increased risk was particularly notable in patients with papillary thyroid carcinoma who received any form of radiation (SIR = 1.69, 95% CI = 1.35–2.09). No higher risk of these skin cancers was observed in patients who did not receive radioactive iodine therapy.

A total of 865 nonkeratinocyte skin cancers were identified following a diagnosis of thyroid cancer, including 790 melanomas. Among these skin cancers, 171 (19.8%) of them were located on the head or neck following radioactive iodine treatment.

While radioactive iodine therapy remains a key treatment for thyroid cancer, associated with reductions in all-cause and cancer-specific mortality, the findings suggested an increased risk for melanoma and nonkeratinocyte skin cancers. The results may support the consideration of routine skin cancer surveillance in thyroid cancer survivors treated with radioactive iodine.

The limitations encompass a small sample size for nonpapillary thyroid cancers and non-White racial and ethnic groups, potential confounding factors not measured, possible sampling bias, and limited treatment data in the SEER registry. The mechanisms driving the increased risk of skin cancer in thyroid cancer survivors, particularly regarding treatment subtypes and subsequent malignancy risk, are not fully understood.

Full disclosures can be found in the published letter.