Immune-mediated Pneumonitis: A Clinical Conundrum in a Patient with Stage IV Lung Adenocarcinoma with a Dramatic and Durable Response to Checkpoint Inhibitor Case Report

Immune checkpoint blockade with pembrolizumab has demonstrated both progression-free survival and overall survival benefit for patients with NSCLC regardless of PD-L1 expression. However, immune-related adverse events, and in particular checkpoint inhibitor pneumonitis (CIP), are common and can complicate the treatment course, duration of response, as well as overall survival. Here we present a patient with stage IV lung adenocarcinoma who experienced a dramatic response following treatment with pembrolizumab, followed by the development of biopsy-proven organizing pneumonia and immune-mediated pneumonitis requiring early treatment discontinuation. The patient has now achieved a near-complete response over 13 months after treatment discontinuation, highlighting the importance of early recognition and management of immune-related adverse events as well as the possibility of durable response despite treatment discontinuation.