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Background: Agents targeting programmed death-1 receptor (PD-1) and its ligand (PD-L1) are showing promising results in non-small-cell lung cancer (NSCLC). It is unknown whether PD-1/PD-L1 are differently expressed in oncogene-addicted NSCLC. Methods: We analysed a cohort of 125 NSCLC patients, including 56 EGFR mutated, 29 KRAS mutated, 10 ALK translocated and 30 EGFR/KRAS/ALK wild type. PD-L1 and PD-1 expression were assessed by immunohistochemistry. All cases with moderate or strong staining (2+/3+) in >5% of tumour cells were considered as positive. Results: PD-1 positive (+) was significantly associated with current smoking status ( P =0.02) and with the presence of KRAS mutations ( P =0.006), whereas PD-L1+ was significantly associated to adenocarcinoma histology ( P =0.005) and with presence of EGFR mutations ( P =0.001). In patients treated with EGFR tyrosine kinase inhibitors ( N =95), sensitivity to gefitinib or erlotinib was higher in PD-L1+ vs PD-L1 negative in terms of the response rate (RR: P =0.01) time to progression (TTP: P <0.0001) and survival (OS: P =0.09), with no difference in PD1+ vs PD-1 negative. In the subset of 54 EGFR mutated patients, TTP was significantly longer in PD-L1+ than in PD-L1 negative ( P =0.01). Conclusions: PD-1 and PD-L1 are differentially expressed in oncogene-addicted NSCLC supporting further investigation of specific checkpoint inhibitors in combination with targeted therapies.

The transmembrane tyrosine kinase mesenchymal-epidermal transition (MET) receptor and its ligand, hepatocyte growth factor, also known as scatter factor, have recently been identified as novel promising targets in several human malignancies, including non-small cell lung cancer (NSCLC). Amplification, mutation, or overexpression of the gene can result in aberrant activation of the MET axis, leading to migration, invasion, proliferation, metastasis, and neoangiogenesis of cancer cells, suggesting that interfering with the MET/hepatocyte growth factor pathway could represent a potential antitumor strategy. While the role of mutations in NSCLC is not as yet fully understood, retrospective studies have shown that an increased gene copy number is a negative prognostic factor. In NSCLC, amplification of the gene is a relatively rare event, occurring in approximately 4% of patients not previously exposed to systemic therapies and in up to 20% of patients with acquired resistance to epidermal growth factor receptor tyrosine kinase inhibitors. In preclinical models, the presence of amplification is a predictor of high sensitivity to anti-MET compounds, and several agents have entered in clinical trials for patients having advanced disease, with promising results. The aim of the present review is to summarize available data on the role of MET in NSCLC and to describe therapeutic strategies under investigation.