Late-onset programmed cell death protein-1 inhibitor-induced pneumonitis after cessation of nivolumab or pembrolizumab in patients with advanced non-small cell lung cancer: a case series.

Awareness of the immune-related adverse event of programmed cell death protein-1 (PD-1) inhibitor-induced pneumonitis is important. Herein, we report the clinical course of 3 patients suspected to have PD-1 inhibitor-induced pneumonitis after cessation of PD-1 inhibitor treatment. In case 1, a 62-year-old man was diagnosed with stage IVA adenocarcinoma. Nivolumab monotherapy was prescribed as second-line therapy and later discontinued due to financial reasons. Seven months after the final administration of nivolumab, the patient developed what we diagnosed as nivolumab-induced pneumonitis. The patient was immediately prescribed prednisolone (1 mg/kg p.o. daily), and the pneumonitis resolved after 1.5 months. In case 2, a 68-year-old man was diagnosed with stage IVB squamous cell carcinoma. Nivolumab monotherapy was prescribed as fourth-line therapy. After the second administration of nivolumab, the patient developed what we diagnosed as nivolumab-induced pneumonitis; nivolumab was discontinued, and the patient was immediately prescribed prednisolone (1 mg/kg p.o. daily). Eight months after the final administration of nivolumab, the patient again developed nivolumab-induced pneumonitis. The pneumonitis resolved without additional medication. In case 3, a 69-year-old man was diagnosed with stage IVB adenocarcinoma. Pembrolizumab monotherapy was initiated as sixth-line therapy, and it was discontinued after 4 cycles due to disease progression. Four months after the final dose of pembrolizumab, the patient developed what we diagnosed as pembrolizumab-induced pneumonitis. The patient immediately received a high intravenous dose of methylprednisolone (1,000 mg per day for three days). The pneumonitis and respiratory failure progressed, and he died 8 weeks after the onset of the pneumonitis. We report pneumonitis after discontinuation of ICIs in 3 patients. We confirm that, although uncommon, PD-1 inhibitor-induced irAEs can develop after treatment discontinuation. Further accumulation of cases and clarification of the clinical features of patients with irAEs, such as the time of onset, imaging findings, and treatment outcomes are needed.