Clinical significance of KL-6 in immune-checkpoint inhibitor treatment for non-small cell lung cancer

Purpose Krebs von den Lungen-6 (KL-6) functions as a tumor marker, as well as a diagnostic tool for interstitial pneumonia (IP). However, the significance of KL-6 in the immune-checkpoint inhibitor (ICI) treatment of non-small cell lung cancer (NSCLC), especially in patients without IP, is unknown. Methods This multicenter, retrospective study, which included patients with advanced NSCLC who received ICI therapy, analyzed the association between serum KL-6 values and ICI efficacy and the association between serum KL-6 values and ICI-induced interstitial lung disease (ILD) occurrence, focusing primarily on patients without IP. Results In total, 322 patients had available KL-6 values before ICI therapy. Among 202 patients without IP who received ICI monotherapy, the high-KL-6 group (≥ 500 U/mL) showed significantly shorter progression-free survival (PFS) and overall survival (OS) than the low-KL-6 group (< 500 U/mL) (median: 2.1 vs. 3.6 months, p = 0.048; median: 9.2 vs. 14.5 months, p = 0.035). There was no significant difference in response rate between the KL-6 high and low groups (19% vs. 29%, p = 0.14). In the multivariate analysis, high KL-6 was a significant predictor of poor PFS (hazard ratio [HR], 1.52; 95% confidence interval [CI] 1.10–2.11, p = 0.012) and OS (HR, 1.51; 95% CI 1.07 − 2.13, p = 0.019) for patients treated with ICI monotherapy. There was no significant difference in the occurrence rate of ILD between the high KL-6 and low KL-6 groups in patients with (20% vs. 15%, p = 1.00) or without IP (12% vs. 12%, p = 1.00). Conclusion In ICI monotherapy for NSCLC without IP, elevated serum KL-6 levels were associated with poorer outcomes.