CASE PRESENTATION: A 71-year-old woman with Stage 3A Adenocarcinoma of the Lung, ex-smoker and COPD, received chemotherapy, had left upper lobectomy in July 2014. Patient had a PET scan in October 2015 which showed hypermetabolic uptake suggestive of recurrent tumor in the left upper lobe and left hilum with worsening subcarinal and mediastinal lymphadenopathy. The patient received total of 6 cycles of Nivolumab by February 2016. This patient presented to ER in March 2016 with shortness of breath for 3 weeks, low-grade fever and cough. She was hypoxic with oxygen saturation of 82% on room air with diffuse rales and rhonchi. CT chest showed new diffuse reticulonodular infiltrates. The patient had a PET scan 3 days prior to admission that showed diffuse, new hypermetabolic infiltrates bilaterally, where as previously seen hilar mass had resolved with improved subcarinal lymphadenopathy. The patient was admitted to the hospital and treated with IV steroids for Pneumonitis with improvement of symptoms and oxygenation.