RBM17 expression is associated with the efficacy of immune checkpoint inhibitor monotherapy in non-small cell lung cancer with low PD-L1 expression

Immune checkpoint inhibitors (ICIs) are currently a standard treatment tool for non-small cell lung cancer (NSCLC). RNA-binding motif protein 17 (RBM17), a splicing factor,is frequently overexpressed in NSCLC, but little is known about the role of RBM17 in the efficacy of ICIs for NSCLC. Thus, we investigated the correlations between RBM17 expression and ICI efficacy in NSCLC. We collected biopsy or surgical specimens from patients with advanced or recurrent NSCLC who received ICI monotherapy or chemo-immunotherapy in a first-line setting. RBM17 expression was examined by immunohistochemistry. We evaluated the correlation between the efficacy of ICI monotherapy or chemo-immunotherapy and RBM17 expression. Among the 218 cases, 115 (52.8%) cases were positive for RBM17 expression. RBM17 expression was not associated with the objective response rate (ORR) or progression-free survival (PFS) in either of the ICI monotherapy or chemo-immunotherapy groups. However, among those with a low PD-L1 expression level (PD-L1 < 50%; n = 86), RBM17 expression was significantly associated with a better ORR (p = 0.045) and a better PFS (p < 0.001) in the ICI monotherapy group, and was significantly associated with a poor ORR in the chemo-immunotherapy group (p = 0.041). In conclusion, RBM17 might be a useful predictive marker for a higher efficacy of ICI monotherapy in NSCLC patients with a low PD-L1 expression level.