Exacerbation of Previously Undiagnosed Bird Fancier’s Lung by Pembrolizumab Therapy

Immune checkpoint inhibitors have revolutionized cancer therapy. As the use of checkpoint inhibitors becomes widespread, the early recognition and treatment of their unique spectrum of adverse effects, called immune-related adverse events, become critical. Perhaps the most significant of these is the pulmonary toxicity currently described as "pneumonitis." However, little is known about the effects of immune checkpoint inhibitors on preexisting interstitial lung disease. We present a case of subclinical hypersensitivity pneumonitis that was exacerbated by pembrolizumab, a programmed cell death-1 inhibitor. This case illustrates a new immune-related adverse event and suggests that exacerbation of preexisting interstitial lung disease is a potential pulmonary toxicity from immune checkpoint inhibitor therapy.