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

Abstract 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.