Severe skin ulcer caused by taking lenvatinib after proton beam therapy

A 69-year-old man was treated with lenvatinib after three sessions of proton beam therapy (PBT) for hepatocellular carcinoma. Five months after administration of lenvatinib, a dermatitis with huge skin ulcer formed in the site of PBT irradiation. Lenvatinib was immediately withdrawn, but the skin ulcer continued growing until about 2 weeks later. With topical and antibiotic treatment, the skin ulcer resolved after about 4 months. After administration of lenvatinib, potential skin damage due to PBT at the irradiated site may have become apparent. This is the first report describing skin ulcer by the combination of lenvatinib administration and PBT.