Response to Idelalisib in a Patient with Stage IV Merkel-Cell Carcinoma

Some Merkel-cell carcinomas have overexpression of phosphoinositide 3-kinase delta. Idelalisib, an inhibitor of this enzyme, induced a dramatic response in an older woman with massive disease spread to the liver. To the Editor: Metastatic Merkel-cell carcinoma is often lethal, and there is no effective treatment. 1 Activation of phosphoinositide 3-kinase (PI3K) in Merkel-cell carcinoma is independent of the presence of the Merkel-cell polyomavirus. 2 , 3 Idelalisib, a selective PI3Kδ inhibitor, has shown remarkable therapeutic efficacy in B-cell hematologic cancers. 4 Here, we report a complete clinical response induced by idelalisib in a patient with stage IV Merkel-cell carcinoma. The patient was an 86-year-old white woman with stage IIIB Merkel-cell carcinoma of the right temple that was diagnosed in 2013 and recurred in 2014. She underwent surgery and received radiation therapy in May 2013, . . .