Abstract
Immunotherapy dramatically changed the management of several malignancies including non-small cell lung cancer (NSCLC). Since immune checkpoint inhibitors have a different mechanism of action from cytotoxic agents or small molecules against NSCLC, also tumor response may present with atypical features. Pseudoprogression (PP) is a distinct response pattern defined by a transient enlargement of the tumor burden, sustained by inflammatory cells and usually not associated with worsening of performance status (PS). Here the authors describe the case of a lung adenocarcinoma patient treated with pembrolizumab, who developed an early symptomatic PP with a dramatic global worsening of PS. Subsequently an improvement in general condition and a brilliant tumor response were observed. Tumor re-biopsy was collected after the treatment in order to support the identification of PP and to describe microenvironment modifications induce by immunotherapy.