Subclinical Hypothyroidism in Childhood Cancer Survivors

Purpose: 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. Materials and Methods: 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). Results: 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. Conclusion: SCH was common in childhood cancer survivors. Brain or nasopharyngeal cancer, lymphoma, and head radiation >= 1800 cGy were significant risk factors for persistent SCH.