Complete Response to Nivolumab in Recurrent/Metastatic HPV-Positive Head and Neck Squamous Cell Carcinoma Patient After Progressive Multifocal Leukoencephalopathy: A Case Report oleh Laura Deborah Locati, Mara Serena Serafini, Andrea Carenzo, Silvana Canevari, Federica Perrone, Ester Orlandi, Serena Delbue, Stefano Cavalieri, Giulia Berzeri, Anna Pichiecchio, Anna Pichiecchio, Lisa Francesca Licitra, Lisa Francesca Licitra, Enrico Marchioni, Loris De Cecco