Blood gene expression changes in metastatic lung cancer under first-line immunotherapy according to clinical response

e21141 Background: First-line pembrolizumab monotherapy is a standard treatment for metastatic non-small-cell lung cancer (NSCLC) with high PD-L1 expression (TPS ≥50%). However, many patients do not respond, and reliable biomarkers are lacking. Methods: Blood samples of 33 patients with metastatic NSCLC were analyzed at baseline (BL) and after four cycles of pembrolizumab monotherapy (FU). The expression of 12 genes involved in tumor-specific immune responses ( FAS, RORgt, FOXP3, IFNγ, FASLv1, PRF1, GATA3, PD1, CD247, GZMB, MKI67, TBX21) in whole blood RNA was quantified by RT-PCR in absolute terms using plasmids as standards. Results: Gene expression was significantly higher after immunotherapy for 11/12 genes analyzed ( FAS, RORgt, FOXP3, IFNγ, FASLv1, PRF1, GATA3, PD1, CD247, GZMB, TBX21 with fold changes [FC] 1.99 – 5.45; all p < 0.001). Blood neutrophil and total leukocyte counts were significantly decreased (ANC BL:7.65/nl vs. FU:5.36/nl, p = 0.024; Leu BL:10.65/nl vs. FU:7.78/nl, p = 0.032), while lymphocyte counts did not change (ALC BL:1.41/nl vs. FU:1.47/nl, p = 0.267). Increases in the expression of RORgt, FASLv1, PRF1, PD1, CD247, GZMB and TBX21 remained significant (FC 1.9 – 3.7; all p < 0.001) even after correction for the blood lymphocyte/leukocyte ratio (Ly/Lc BL:0.151 vs. FU:0.197, p = 0.003). Patients with long-term response (LTR, i.e. lasting > 6 months) had significantly higher increases in the expression of 8 genes ( RORgt, FOXP3, IFNγ, FASLv1, GATA3, PD1, CD247, TBX21) compared with patients with rapid disease progression within 3 months (RP) (FC 2.34 – 4.62, all p < 0.05). There were no significant differences (FU-BL) between LTR and RP regarding ANC (RP:-1.00/nl vs. LTR:-2.63/nl, p = 0.50), ALC (RP:-0,14/nl vs. LTR:+0,12/nl, p = 0,33) or Ly/Lc (RP:0.015 vs. LR:0.0542, p = 0.259). Conclusions: Pembrolizumab monotherapy of metastatic NSCLC causes significant increases in the blood expression for several genes including FAS, RORgt, FOXP3, IFNγ, FASLv1, PRF1, GATA3, PD1, CD247, GZMB, TBX21, as well as a decrease in circulating neutrophiles and total leucocytes. Long-term responders have more pronounced blood gene expression changes, which appear to correlate with long-term benefit, in contrast to blood count changes, which are not indicative. These results are currently being validated in a larger prospective study.