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started treatment with Erdafitinib at the age of 15 years and four months [18]. At the time, his Tanner staging was delayed and estimated at stage 2–3. The initial daily dose of 7 mg erdafitinib, taken orally for 5 months, required frequent interruptions of therapy due to high phosphorus levels (Table 1) and requiring administration of high doses of oral phosphate binders. He was not on any glucocorticoids during the erdafitinib treatment. When he transferred care, due to relocation, the dose of erdafitinib was reduced to 5 mg daily resulting in fewer treatment interruptions.
Despite a remarkable tumor response, with an approximately 80 percent reduction in tumor volume and contrast enhancement on magnetic resonance imaging or MRI (Supplemental Fig. 1) erdafitinib had to be discontinued due to the patient's unusual rapid growth over the 9 months of therapy, severe kyphoscoliosis, and spinal cord compression with cervical myelopathy. The patient grew a total of 14.3 cm, or at an annualized growth of 19.06 cm (normal growth is ∼10 cm per year for a 15-year-old male). Growth prior to erdafitinib therapy was at the 16th to 25th percentile for height and shifted to the 70th percentile during therapy (Fig. 1). The rapid growth led to skeletal deformities which were visible on X-rays, when compared to normal cervical and thoracic spine before erdafitinib treatment (Fig. 2A–a to c). Cervical lordosis and thoracic scoliosis were evident after 9 months of erdafitinib treatment (Fig. 2A, d-i). MRI imaging of the cervical, thoracic and lumbar spine showed the development of deformities after commencing systemic erdafitinib therapy (Fig. 2B–a-d). Of note, he also developed hip flexor contractures not visualized on the imaging, resulting in an underestimation of his height measurements. The cranial vault (membranous bone), unlike cartilaginous skeletal bones, appeared to be unaffected. He returned to our medical center for surgical correction of his symptomatic kyphoscoliosis after cessation of therapy
Despite a remarkable tumor response, with an approximately 80 percent reduction in tumor volume and contrast enhancement on magnetic resonance imaging or MRI (Supplemental Fig. 1) erdafitinib had to be discontinued due to the patient's unusual rapid growth over the 9 months of therapy, severe kyphoscoliosis, and spinal cord compression with cervical myelopathy. The patient grew a total of 14.3 cm, or at an annualized growth of 19.06 cm (normal growth is ∼10 cm per year for a 15-year-old male). Growth prior to erdafitinib therapy was at the 16th to 25th percentile for height and shifted to the 70th percentile during therapy (Fig. 1). The rapid growth led to skeletal deformities which were visible on X-rays, when compared to normal cervical and thoracic spine before erdafitinib treatment (Fig. 2A–a to c). Cervical lordosis and thoracic scoliosis were evident after 9 months of erdafitinib treatment (Fig. 2A, d-i). MRI imaging of the cervical, thoracic and lumbar spine showed the development of deformities after commencing systemic erdafitinib therapy (Fig. 2B–a-d). Of note, he also developed hip flexor contractures not visualized on the imaging, resulting in an underestimation of his height measurements. The cranial vault (membranous bone), unlike cartilaginous skeletal bones, appeared to be unaffected. He returned to our medical center for surgical correction of his symptomatic kyphoscoliosis after cessation of therapy
