Lung squamous cell carcinoma responding to nivolumab retreatment six years after initial treatment: A case report.

A 61-year-old man presented to our hospital with a chief complaint of chronic cough. He was diagnosed with lung squamous cell carcinoma at clinical stage cT2aN3M1a. He received chemotherapy up to the fourth line, but both the primary tumor and lymph node metastases increased in size. Nivolumab, administered as the fifth line, resulted in a complete response (CR) that continued for 2 years and 8 months. Treatment was stopped due to the appearance of common terminology criteria for adverse events grade 1 pneumonitis. He was followed up without treatment for 3 years and 8 months, but a left supraclavicular fossa lymph node metastasis appeared. Retreatment with nivolumab was initiated, and the patient achieved CR again. One year and 6 months after retreatment, CR was maintained with nivolumab. This case represents a rare instance in which nivolumab yielded a significant response after a prolonged immune checkpoint inhibitor (ICI)-free interval. Our experience has shown that the long-term response to ICIs may deteriorate in the future. Therefore, retreatment with ICIs may be effective when the initial therapy is successful.