Erdafitinib-Induced Flexural Calcinosis Cutis in a Pediatric Patient: A Drug-Specific Side-Effect?

Fibroblast growth factor receptor (FGFR) inhibitors are effective in malignancies with FGFR pathway alterations but may disrupt calcium-phosphate metabolism, leading to dermatologic side effects. We report a case of calcinosis cutis presenting as painful flexural plaques in a 16-year-old patient treated with erdafitinib for high-grade glioma. The patient's age, unusual lesion distribution, and spontaneous resolution after drug discontinuation highlight a previously unreported association in pediatrics. Recognizing this potential adverse effect may help avoid unnecessary diagnostic or therapeutic interventions.