MON-LB016 Tyrosine Kinase Inhibitor Induced Hypothyroidism in Pediatric and Young Adult Population: An Institutional Review

Abstract

Tyrosine Kinase Inhibitor Induced Hypothyroidism in Pediatric and Young Adult Population: An institutional reviewBackground:Tyrosine kinase inhibitors (TKIs) are a class of molecular targeted therapies approved for the treatment of several hematological and solid tumors in pediatric population. Thyroid dysfunction, most commonly primary hypothyroidism, is a well described adverse effect in adults. There is no available data in the pediatric population regarding the risk of thyroid dysfunction with the use of TKIs.Objective:To document the incidence of hypothyroidism in the pediatric and young adult patients on TKI therapy.Methods:A retrospective chart review including patients’ ≤ 21 years of age who had been treated with at least 1 of 10 predetermined TKIs for malignancy was performed. Demographics, TKI use and duration, thyroid hormone labs, and history of head/neck radiation were collected. We excluded patients with pre-existing thyroid disease prior to start of TKI therapy. Thyroid dysfunction was defined as TSH >5mcIU/mL during TKI therapy. Results:A total of 152 patients who were treated with TKIs for malignancy were identified. The mean age was 12.4 years (SD 6.5). About 20% of patients had therapy with multiple TKI drugs. A total of 24 patients were noted to have TSH elevation >5mcIU/ml of which 19 had a TSH >10 mcIU/mL or low free T4. Fourteen patients were started on levothyroxine. Average duration of TKI therapy prior to development of thyroid dysfunction was 6.7 months but over half developed hypothyroidism within 3 months of initiation of TKI therapy. Cabozantinib and pazopanib were responsible for 70% of TKI associated cases of thyroid dysfunction.Conclusion:This is the first report of incidence of primary hypothyroidism in pediatric and young adult patients treated with TKIs. Thyroid dysfunction can develop in the first few months of therapy and often is clinically significant. Early recognition and treatment of this complication will be important for patient care especially as use of these class of drugs increase.