Subclinical Hypothyroidism in Childhood Cancer Survivors

In childhood cancer survivors, the most common late effect is thyroid dysfunction, most notably subclinical hypothyroidism (SCH). Our study evaluated the risk factors for persistent SCH in survivors. Survivors (n=423) were defined as patients who survived at least 2 years after cancer treatment completion. Thyroid function was assessed at this time and several years thereafter. Two groups of survivors with SCH were compared: those who regained normal thyroid function during the follow-up period (normalized group) and those who did not (persistent group). Overall, 104 of the 423 survivors had SCH. SCH was observed in 26% of brain or nasopharyngeal cancer survivors (11 of 43) and 21.6% of leukemia survivors (35 of 162). Sixty-two survivors regained normal thyroid function, 30 remained as persistent SCH, and 12 were lost to follow-up. The follow-up duration was 4.03 (2.15-5.78) years. Brain or nasopharyngeal cancer and Hodgkin disease were more common in the persistent group than in the normalized group (p=0.002). More patients in the persistent group received radiation (p=0.008). Radiation to the head region was higher in this group (2394±2469 cGy) than in the normalized group (894±1591 cGy; p=0.003). On multivariable analysis, lymphoma (p=0.011), brain or nasopharyngeal cancer (p=0.039), and head radiation dose ≥1800 cGy (p=0.039) were significant risk factors for persistent SCH. SCH was common in childhood cancer survivors. Brain or nasopharyngeal cancer, lymphoma, and head radiation ≥1800 cGy were significant risk factors for persistent SCH.