A Case of Long-Term Survival after Checkpoint InhibitorPneumonitis in a Patient with Squamous Cell Lung Cancer

The management of grade 1 checkpoint inhibitor pneumonitis (CIP) is to withhold immune checkpoint inhibitors; however, thenatural history of this condition is unknown. We herein report the case of a woman with squamous cell lung cancer who was along-term survivor after CIP. After 4 rounds of treatment with nivolumab, a chest CT revealed a reticular pattern and ground-glass attenuation with shrinkage of the primary nodule. Nivolumab treatment was withheld without the administration ofsteroids. Although she remained asymptomatic, subsequent images revealed an increasing interstitial shadow until 2 monthsafter the stop of nivolumab treatment. Thereafter, the interstitial shadow began to improve spontaneously without steroidtreatment. Moreover, although the patient has not received additional therapy, disease control of lung cancer has been obtainedwithin a follow-up period of more than 3 years. Although the exacerbation of CIP may appear on images for several months,asymptomatic cases can be followed without the administration of steroids. If the tumor had already responded prior to theonset of CIP, a favorable long-term prognosis can be expected.