Risk factors for relapse of immune-related pneumonitis after 6-week oral prednisolone therapy: a follow-up analysis of a phase II study.

Background: Immune-related pneumonitis (irP) is one of the most important immune-related adverse events caused by immune checkpoint inhibitors (ICIs). After corticosteroid therapy irP frequently relapses, which can interfere with cancer therapy. However, risk factors for irP relapse are unknown.

Methods: This study was a follow-up analysis of a phase II study that evaluated 56 patients with grade ≥ 2 irP treated with oral prednisolone, 1 mg/kg/day, tapered over 6 weeks. Clinical factors including patient characteristics, blood test findings, and response to prednisolone therapy were assessed to identify risk factors for irP relapse using the Fine-Gray test.

Results: Among 56 patients with irP, 22 (39.3%) experienced irP relapse after 6 weeks of prednisolone therapy during the follow-up observation period. Radiographic organising pneumonia (OP) pattern and duration to irP onset ≥ 100 days from ICI initiation were determined to be significant risk factors for irP relapse in a multivariate Fine-Gray test (hazard ratio [HR] = 3.17, 95% CI 1.37-7.32, p = 0.007, and HR = 2.61, 95% CI 1.01-6.74, p = 0.048, respectively). Other patient characteristics, blood test findings, irP severity, and response to prednisolone therapy were not associated with irP relapse.

Conclusions: In irP patients treated with 6-week prednisolone tapering therapy, OP pattern and duration to irP onset ≥ 100 days were associated with relapse risk. Assessment of the risk factors for irP relapse will be helpful for irP management.