A case of erythema multiforme-like rash induced by everolimus in a patient with a pancreatic neuroendocrine tumor

A 66-year-old Japanese woman had been diagnosed with a neuroendocrine tumor of the pancreatic head (G2) 3 years previously and undergone pancreaticoduodenectomy. Nine months postoperatively, recurrence with multiple liver metastases developed and she was referred to our department. A regimen of 10 mg of everolimus for 2 weeks plus 1-week washout was instituted, and no adverse events were observed. Fourteen months after treatment initiation, she developed severe generalized erythema multiforme (EM). Skin biopsy revealed spongiosis in the epidermis and interface change and edema in the superficial dermis. Mast cells were observed from the dermis to the subcutaneous tissue, as well as perivascular eosinophilic infiltration, leading to EM being diagnosed. Oral everolimus was discontinued, and the EM was relieved by treatment including steroid therapy. Everolimus is an inhibitor of the mammalian target of rapamycin, and its indications include neuroendocrine tumors. Skin disorders are commonly seen in the early stages of everolimus treatment, but their severity is almost always mild and never severe. This is the first report on a patient who presented with severe generalized EM more than 1 year after everolimus treatment initiation. Patients on everolimus therapy should be monitored for skin disorders on a long-term basis.