Clinical Analysis of Relapse Risk in Immune-Checkpoint-Inhibitor-Related Pneumonitis

Background: While immune checkpoint inhibitor (ICI)-related pneumonitis (CIP) may relapse during or after steroid treatment, clinical factors associated with CIP relapse are unclear. This study explored risk factors potentially associated with CIP relapse. Methods: This single-center retrospective study included 1099 patients who received ICIs at our institution between April 2015 and March 2022. Among them, 39 patients who developed CIP and were treated with systemic steroids and tapered to prednisolone (PSL) ≤ 20 mg/day were analyzed. Patients were classified into relapse and non-relapse groups based on whether CIP recurred during or after steroid treatment. Patient characteristics, clinical features at onset, and treatment strategies were compared between the two groups. Results: Thirteen patients (33.3%) experienced relapse. Compared with the non-relapse group, the relapse group had a significantly higher proportion of non-smokers (30.8 vs. 3.3%, p = 0.035), a greater frequency of Common Terminology Criteria for Adverse Events (CTCAE) Grade 2 pneumonitis (92.3 vs. 53.8%, p = 0.029), and lower serum KL-6 levels (288 vs. 704 U/mL, p = 0.014). The relapse group also had a shorter duration of steroid therapy at the initial dose, ≥0.5 mg/kg/day, ≥15 mg/day, and ≥20 mg/day (p < 0.05) and lower cumulative steroid doses (1140 vs. 1902 mg, p = 0.015). Relapse tended to occur in patients with relatively mild pneumonitis who received lower steroid doses and shorter treatment durations. Conclusions: Non-smoking status, CTCAE Grade 2 pneumonitis, lower serum KL-6 levels, shorter duration of steroid therapy, and lower cumulative steroid dose were potentially associated with CIP relapse. Adequate steroid dosing and tapering may help prevent relapse.