P76.58 Osimertinib for EGFR-Positive NSCLC Patients with Leptomeningeal Metastases Harboring T790M-Positive or T790M-Negative Mutations

Abstract

distribution of patients with different PD-L1 TPS values, followed by analysis of response rate (RR), survival rate, and incidence of secondary T790M mutation according to the PD-L1 TPS group. Results: Among the 131 patients analyzed, the proportion of patients with PD-L1 TPS 50%, 1%-49%, and < 1%, was 17.6%, 32.8%, and 49.6%, respectively. The RR was significantly lower in the group with PD-L1 TPS 50% than in the other groups (43.5% vs. 72.1% vs. 78.5%, all p ¼ 0.001). In multivariate analysis, PD-L1 TPS 50% was independently associated with a significantly shorter PFS in the overall population (hazard ratio [HR] ¼ 2.64, p ¼ 0.004), and associated with shorter OS in patients with exon 19 deletion (HR ¼ 2.55, p ¼ 0.041) compared with PD-L1 TPS < 50%. In addition, the frequency of secondary T790M mutation after TKI failure was significantly lower in the group with PD-L1 TPS 50% than in the other groups (13.3% vs. 40.0% vs. 53.3%, all p ¼ 0.001). PD-L1 TPS 50% was an independent predictor of a lower frequency of this mutation (HR ¼ 0.63, p ¼ 0.043). Conclusion: High PD-L1 expression was associated with unfavorable clinical outcome, and less development of secondary T790M mutation, suggesting a distinct subgroup warranting active surveillance and tailored therapeutic approach.