Background

In non-small cell lung cancer (NSCLC), mesenchyme to epithelial transition (MET) protein abundance increases with disease stage and is implicated in resistance to tyrosine kinase inhibitors. To better clarify the impact of MET overexpression on tumor behavior, we investigated a large cohort of patients who underwent curative surgical resection to determine whether MET gene amplification or protein abundance was prognostic.

Methods

Tissue microarrays (TMAs) were constructed using triplicate 1 mm cores of FFPE primary NSCLC specimens. TMAs underwent immunohistochemical (IHC) staining with the SP44 clone (Ventana) and cores were considered positive if >50% of tumor exhibited 2+ staining. The highest of triplicate values was used. MET gene amplification was detected using either SISH using Ventana's MET DNP probe or FISH using the D7S486/CEP 7 Abbott Probe. DNA was subjected to mutational profiling using Sequenom's LungCarta panel.

Results

Data from two institutions comprising 763 patients (516; 68%) male were generated, including 360 stage I, 226 stage II, 160 stage III and 18 resected stage IV. High MET protein expression was detected in 25% (193/763), and was significantly more common in adenocarcinomas than squamous cell carcinoma (P<0.01). MET gene copy number (GCN) correlated with high MET protein expression by IHC (P=0.01). Increased MET protein expression was associated with EGFR and KRAS mutations (P<0.01 for both). Once polysomy was excluded, true MET gene amplification was detected in only 8/763 (1%) of samples. In multivariate analysis, neither MET protein abundance nor GCN were correlated to overall patient survival.

Conclusions

MET expression by IHC and GCN amplification was not prognostic in this large Caucasian surgical series. MET's primary role remains as a therapeutic target.

Introduction

Immune checkpoint inhibition has shifted treatment paradigms in non-small cell lung cancer (NSCLC). Conflicting results have been reported regarding the immune infiltrate and programmed death-ligand 1 (PD-L1) as a prognostic marker. We correlated the immune infiltrate and PD-L1 expression with clinicopathologic characteristics in a cohort of resected NSCLC.

Methods

A tissue microarray was constructed using triplicate cores from consecutive resected NSCLC. Immunohistochemistry was performed for CD8, FOXP3 and PD-L1. Strong PD-L1 expression was predefined as greater than 50% tumor cell positivity. Matched nodal samples were assessed for concordance of PD-L1 expression.

Results

Of 522 patients, 346 were node-negative (N0), 72 N1 and 109 N2; 265 were adenocarcinomas (AC), 182 squamous cell cancers (SCC) and 75 other. Strong PD-L1 expression was found in 24% cases. In the overall cohort, PD-L1 expression was not associated with survival. In patients with N2 disease, strong PD-L1 expression was associated with significantly improved disease-free (DFS) and overall survival (OS) in multivariate analysis (HR 0.49, 95%CI 0.36-0.94, p = 0.031; HR 0.46, 95%CI 0.26-0.80, p = 0.006). In this resected cohort only 5% harboured EGFR mutations, whereas 19% harboured KRAS and 23% other. KRAS mutated tumors were more likely to highly express PD-L1 compared to EGFR (22% vs 3%). A stromal CD8 infiltrate was associated with significantly improved DFS in SCC (HR 0.70, 95%CI 0.50-0.97, p = 0.034), but not AC, whereas FOXP3 was not prognostic. Matched nodal specimens (N = 53) were highly concordant for PD-L1 expression (89%).

Conclusion

PD-L1 expression was not prognostic in the overall cohort. PD-L1 expression in primary tumor and matched nodal specimens were highly concordant. The observed survival benefit in N2 disease requires confirmation.