Late-onset recurrent immune checkpoint inhibitor-related pneumonitis after cessation of pembrolizumab: a case report

Immune-related adverse events typically occur during the early phases of immune checkpoint inhibitor therapy. However, late-onset immune-related adverse events can still arise long after the immune checkpoint inhibitor therapy has ended. Immune checkpoint inhibitor-related pneumonitis warrants special attention for risk assessment and early detection due to its potential for serious outcomes, including hospitalization and death. Despite its rarity, late-onset immune checkpoint inhibitor-related pneumonitis should be considered in the differential diagnosis for dyspnea in patients with a history of immune checkpoint inhibitor therapy to prevent morbidity and mortality. In this case report, we present a case of an 84-year-old female patient suffering from locally advanced triple-negative breast cancer and late-onset immune checkpoint inhibitor-related pneumonitis requiring hospitalization 104 days after the last cycle of pembrolizumab. Following successful treatment of late-onset immune checkpoint inhibitor-related pneumonitis with corticosteroids, a recurrence of immune checkpoint inhibitor-related pneumonitis occurred a month later. Corticosteroid therapy was reinitiated, gradually tapered after radiological improvement, and eventually discontinued. The patient remains in remission from breast cancer. For patients with a history of immune checkpoint inhibitor therapy, medical vigilance, accurate diagnosis, and timely management of late-onset immune checkpoint inhibitor-related pneumonitis are crucial.