CASE PRESENTATION: A 56 year old female with past medical history of stage III C breast cancer status post radical modified mastectomy and lymph node dissection presented to our hospital with acute hypoxic respiratory failure. She previously had undergone treatment with different chemotherapeutic agents in addition to radiation for management of recurrent malignant disease. Due to progression of her disease on follow up imaging, patient was started on Nivolumab before her presentation. Workup included a CT angiogram that was negative for pulmonary embolism, but showed stable lymphadenopathy and new bilateral ground glass opacities in the upper lobes left greater than the right. Patient refused to undergo invasive biopsy procedure and was placed on steroids for empiric treatment of hypersensitivity pneumonitis to which she responsed and was discharged home.