Abstract
BACKGROUND/AIM: The association between tumor PD-L1 expression and the rate of acquisition of the T790M mutation during treatment with first-/second-generation epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) is a matter of study. This retrospective study was conducted to evaluate the association of tumor PD-L1 expression with the time on treatment under EGFR-TKIs in patients with EGFR-mutant non-small cell lung cancer (NSCLC), treated with first-/second-generation EGFR-TKIs. PATIENTS AND METHODS: We conducted a retrospective review of the medical charts of patients with EGFR-mutant NSCLC treated with first- /second-generation EGFR-TKIs. Time on treatment with EGFR-TKIs was defined as the sum of progression-free survival period (PFS) from the start of treatment with first- /second-generation EGFR-TKIs and the PFS from the start of osimertinib treatment after acquisition of the T790M mutation. Tumor PD-L1 expression was evaluated using the 22C3 antibody. RESULTS: Data of a total of 49 patients were analyzed, including 20 patients with negative tumor PD-L1 expression (tumor proportion score <1%) and 29 patients with positive tumor PD-L1 expression (tumor proportion score ≥1%). In the negative tumor PD-L1 expression group, the T790M mutation was detected in 12 (75%) of the 16 patients. In the positive tumor PD-L1 expression group, the T790M mutation was detected 6 (31.6%) out of the 19 patients in whom it was tested. The median (95% confidence interval) time on treatment with EGFR-TKIs was 21.7 (12.9-24.8) months and 12.3 (5.6-22.2) months in the negative and positive tumor PD-L1 expression groups, respectively. Analysis using a Cox proportional hazards model identified performance status and presence/absence of tumor PD-L1 expression as significantly associated with the time on treatment with EGFR-TKIs. CONCLUSION: EGFR-mutant NSCLC patients with negative tumor PD-L1 expression showed a higher rate of acquisition of the T790M mutation and implementation rate of osimertinib therapy, leading to a longer time on treatment with EGFR-TKI.