Biomarker Analyses from a Placebo-Controlled Phase II Study Evaluating Erlotinib ± Onartuzumab in Advanced Non–Small Cell Lung Cancer: MET Expression Levels Are Predictive of Patient Benefit

Abstract

Purpose In a recent phase II study of onartuzumab (MetMAb), patients whose non–small cell lung cancer (NSCLC) tissue scored as positive for MET protein by immunohistochemistry (IHC) experienced a significant benefit with onartuzumab plus erlotinib (O+E) versus erlotinib. We describe development and validation of a standardized MET IHC assay and, retrospectively, evaluate multiple biomarkers as predictors of patient benefit. Experimental Design Biomarkers related to MET and/or EGF receptor (EGFR) signaling were measured by IHC, FISH, quantitative reverse transcription PCR, mutation detection techniques, and ELISA. Results A positive correlation between IHC, Western blotting, and MET mRNA expression was observed in NSCLC cell lines/tissues. An IHC scoring system of MET expression taking proportional and intensity-based thresholds into consideration was applied in an analysis of the phase II study and resulted in the best differentiation of outcomes. Further analyses revealed a nonsignificant overall survival (OS) improvement with O+E in patients with high MET copy number (mean ≥5 copies/cell by FISH); however, benefit was maintained in “MET IHC-positive”/MET FISH-negative patients (HR, 0.37; P = 0.01). MET, EGFR, amphiregulin, epiregulin, or HGF mRNA expression did not predict a significant benefit with onartuzumab; a nonsignificant OS improvement was observed in patients with high tumor MET mRNA levels (HR, 0.59; P = 0.23). Patients with low baseline plasma hepatocyte growth factor (HGF) exhibited an HR for OS of 0.519 (P = 0.09) in favor of onartuzumab treatment. Conclusions MET IHC remains the most robust predictor of OS and progression-free survival benefit from O+E relative to all examined exploratory markers.

The Therapeutic Potential of Targeting the HGF/cMET Axis in Ovarian Cancer

“…The majority of the estimates above come from IHC studies, using a number of different antibodies, but no consensus on scoring criteria yet exists, nor whether cytoplasmic or membranous staining for cMET is important. Work performed by Koeppen and colleagues has described the validation of the CONFIRM anti-total cMET (SP44) rabbit monoclonal antibody on formalin-fixed paraffin-embedded tissue as part of the phase II trial testing onartuzumab in non-small cell lung cancer [78]. Using cell lines with known levels of cMET expression, comparisons between SP44 antibody staining, flow cytometry (using a different anti-Met antibody), and mRNA levels, it was determined that the SP44 antibody specifically recognises cMET, and not the closely-related Ron receptor.…”

“…Using cell lines with known levels of cMET expression, comparisons between SP44 antibody staining, flow cytometry (using a different anti-Met antibody), and mRNA levels, it was determined that the SP44 antibody specifically recognises cMET, and not the closely-related Ron receptor. Furthermore, a comprehensive clinical scoring system was determined, which enabled a cut-off of 50% (of cells stained moderate/strong) to be utilised in the trial to differentiate patient outcomes when treated with onartuzumab [78]. …”

“…Other studies have used gene amplification (GA) or gene copy number (GCN) to determine if cMET has been amplified (either the gene itself, or larger portions of chromosome 7) [80,81,73,78] although the usefulness of cMET genetic amplification as a biomarker, and its correlation to drug sensitivity, has yet to be validated in large scale trials. Similarly, the correlation between copy number, protein expression level, and responsiveness to cMET-inhibitory agents is still under investigation [78].…”

“…Similarly, the correlation between copy number, protein expression level, and responsiveness to cMET-inhibitory agents is still under investigation [78].…”

Analytical Validation of BRAF Mutation Testing from Circulating Free DNA Using the Amplification Refractory Mutation Testing System

“…As a result, MET protein overexpression in unselected NSCLC cases has been reported to range from 20% to 70%. 137,138 An MA has found that MET expression by IHC in NSCLC is a negative prognostic factor in patients with surgically resected NSCLC. 107 A frequently used commercially available antibody, particularly in clinical trials, is the CONFIRM anti-total MET (SP44) rabbit monoclonal primary antibody (Ventana Medical Systems, Tucson, Arizona) directed against a membranous and cytoplasmic epitope of MET.…”