Adverse dermatologic effects of erdafitinib in a patient with metastatic urothelial carcinoma

Erdafitinib is a fibroblast growth factor receptor 1-4 inhibitor used for locally advanced or metastatic urothelial carcinoma in patients who have experienced disease progression after at least 1 prior systemic therapy. Various cutaneous side effects of erdafitinib have been reported, most commonly stomatitis and nail changes such as onycholysis, nail dystrophy, and paronychia. However, onychomadesis is a rarer nail toxicity that can cause significant discomfort and may necessitate treatment interruption. We present the case of a 61-year-old White man with metastatic urothelial carcinoma treated with 8 mg of erdafitinib daily who developed diffuse onychomadesis within a few months of initiating therapy. Awareness of the potential cutaneous side effects of erdafitinib and timely referral for specialty dermatologic care are important to allow treatment continuation.