Resolution of Erythema Annulare Centrifugum With Lung Cancer Drug Therapy: A Case Report.

Tumor-associated erythema annulare centrifugum is commonly observed in leukemia and lymphoma. In this case, we reported erythema annulare centrifugum associated with lung cancer that resolved following targeted drug therapy. A 71-year-old man with psoriasis visited our hospital with erythema annulare and pruritus. Initially, he was prescribed cyclosporine at a dose of 2.5 mg/kg suspecting a worsening of his psoriasis; however, this treatment was ineffective. Signs of paraneoplastic skin syndrome were observed, leading to a diagnosis of epidermal growth factor receptor mutation-positive lung adenocarcinoma (cT3N2M1c, stage IV, exon 19 del). After initiating osimertinib at a dose of 80 mg, the skin rash improved, and the tumor size was reduced. The final diagnosis was paraneoplastic erythema annulare centrifugum associated with lung cancer. This case highlights the potential resolution of erythema annulare centrifugum through lung cancer therapy, emphasizing the importance of considering lung cancer differential diagnosis when this skin condition is present.