Intensified Inflammatory Reaction of Actinic Keratoses after Single Application of Topical 5-Fluorouracil in a Patient Treated with Nilotinib for Chronic Myeloid Leukemia

Actinic keratoses frequently occur in sun-exposed areas of the skin and, today, a variety of therapeutic options are available, including topical application of 5-fluorouracil (5-FU). Usually, 5-FU ointment needs to be applied twice daily for 2–4 weeks to achieve a therapeutic skin reaction. Here, we report on an immediate inflammatory reaction after single application of topical 5-FU in a patient receiving systemic treatment with the multitargeted tyrosine kinase inhibitor nilotinib for chronic myeloid leukemia. This side effect of nilotinib is new and might be of clinical relevance. We, therefore, discuss possible modes of action including other reports about different tyrosine kinase inhibitors which led to regression of aggravation of actinic keratoses.