Association of baseline peripheral-blood eosinophil count with immune checkpoint inhibitor-related pneumonitis and clinical outcomes in patients with non-small cell lung cancer receiving immune checkpoint inhibitors

Objectives Immune checkpoint inhibitors (ICIs) have revolutionized the oncologic treatment landscape, but have been accompanied by immune-related adverse events (irAEs). ICI-related pneumonitis (ICI-pneumonitis) is a potentially fatal irAE. However, the risk factors associated with ICI-pneumonitis remain unclear. There is an urgent need to identify risk factors for ICI-pneumonitis using reliable and accessible parameters. Here, we aimed to identify baseline peripheral-blood biomarkers correlated with ICI-pneumonitis and clinical outcomes in patients with advanced non-small cell lung cancer (NSCLC) who were treated with ICIs. Materials and Methods We conducted a retrospective analysis of eligible patients with advanced NSCLC who were treated with ICIs at our center. Receiver operating characteristic (ROC) curve was used to determine the optimal cutoff value for analyzing risk of ICI-pneumonitis. Multivariate logistic analysis was performed to identify risk factors of ICI-pneumonitis. Clinical characteristics and treatment outcomes were collected and compared according to the optimal cutoff value. Results A total of 300 patients were included, in which 54 patients (18 %) experienced ICI-pneumonitis. Patients with ICI-pneumonitis had a high level of baseline peripheral-blood absolute eosinophil count (AEC) than those without ICI-pneumonitis (P = 0.013). The optimal threshold of baseline peripheral-blood AEC to predict ICI-pneumonitis was 0.125 × 109 cells/L. The incidence of ICI-pneumonitis was higher in the high-AEC group (AEC ≥ 0.125 × 109 cells/L; 27.7 %) than in the low-AEC group (AEC < 0.125 × 109 cells/L; 9.8 %, P < 0.001). Moreover, patients with high AEC (compared with those with low AEC) had a higher objective response rate (ORR) (40.9 % versus 28.8 %, P = 0.029) and longer median progression-free survival (PFS) (8.93 months versus 5.87 months, P = 0.038). Conclusions Among patients treated with ICIs, a baseline feature of high AEC (≥0.125 × 109 cells/L) was associated with an increasing risk of ICI-pneumonitis, and with a better clinical outcome.