Treatment of Metastatic Extramammary Paget Disease with Combination Ipilimumab and Nivolumab: A Case Report.

Metastatic primary cutaneous extramammary Paget disease (EMPD) is a rare clinical entity with a 5-year survival <10% and no standard therapy. We report the first case to our knowledge of metastatic EMPD with treatment response to checkpoint inhibitor immunotherapy. The patient had diffusely metastatic disease and previously progressed on cytotoxic chemotherapy and a molecularly targeted agent. Treatment with four cycles of ipilimumab 1 mg/kg plus nivolumab 3 mg/kg resulted in a durable partial response lasting 7 months. Analysis of metastatic tumor tissue failed to identify known predictors of treatment response to immune checkpoint inhibitors, such as high PD-L1 expression, high tumor mutation burden, or microsatellite instability. These findings support further investigation of immune checkpoint inhibition for the management of metastatic EMPD, which currently has an abysmal prognosis and no standard therapies.