Frequency and Severity of Hypothyroidism During TKI Therapy in the Pediatric and Young Adult Population.

Tyrosine kinase inhibitors that target vascular endothelial growth factor receptor [VEGFR-TKI] are a class of targeted therapies approved for treatment of several malignancies and are increasingly used in the pediatric population. Development of hypothyroidism during VEGFR-TKI therapy is well described in adults; however, there are no available data in children. Importantly, hypothyroidism during childhood can negatively impact growth and neurodevelopment. This retrospective study is the first to document frequency and severity of VEGFR-TKI induced hypothyroidism in pediatric and young adult patients. Patients included were ≤25 years of age and treated with at least one VEGFR-TKI between 2010 and 2018 at Cincinnati Children's Hospital Medical Center. After review of clinical and demographic data, 69 patients were identified. Of these, 19 (27.5%) developed thyroid dysfunction defined as Thyroid-stimulating hormone≥5 mIU/mL during therapy. Twelve of those patients had overt hypothyroidism with documentation of low free thyroxine and/or levothyroxine initiation. Mean exposure time to VEGFR-TKI before thyroid dysfunction was 2.8 (0.5-10.4) months. These results suggest moderate risk of developing thyroid dysfunction during VEGFR-TKI therapy in pediatric and young adult patients. Baseline thyroid hormone screening should be performed and repeated frequently during the first year of therapy in the pediatric population.