Characterization and Clinical Validation of an Immunohistochemical Assay for Met in Non-Small Cell Lung Cancer
Hartmut Koeppen, Tom Januario, Ellen Filvaroff, Penny Towne, Racheal James, Patrick Roche, Xiaoling Xia, Jiping Zha, Bob Yauch. Genentech, Inc., South San Francisco, CA; Ventana Medical Systems, Inc., Tucson, AZ
Background: The MET gene encodes a transmembrane receptor tyrosine kinase, which is the receptor for hepatocyte growth factor and is expressed on a variety of normal epithelial cells and carcinomas. For some tumor types, expression of Met has been correlated with poor clinical outcome. To develop a standardized Met IHC assay for FFPE tissue needed to definitively determine the prognostic and predictive implications for Met expression we evaluated the performance of a rabbit monoclonal anti-Met Ab (SP44).
Design: Immunohistochemistry (IHC) for Met was performed on formalin-fixed, paraffin-embedded cell pellets and tissues on an automated platform (Ventana Benchmark XT) using a rabbit monoclonal antibody (SP44; Ventana Medical Systems) generated against the intracellular domain of Met. The cell staining intensity for Met was scored as none, weak, moderate or strong. For NSCLC tumor samples a comprehensive clinical scoring system was developed to account for the heterogeneity of Met expression seen in tumor tissue. The scoring system evaluates both, staining intensity and percent cells staining at a given level. NSCLC cases expressing moderate or strong levels of Met in ≥50% of tumor cells (clinical IHC score 2+ or 3+) were classified as Met diagnostic positive (Met Dx+).
Results: IHC for Met on FFPE sections of cell lines expressing Met at various levels (endogenously and manipulated through ectopic transfection of MET or after RNA-interference knockdown) showed excellent correlation between IHC scores and Western blot results. The pre-clinical evaluation demonstrated excellent specificity and sensitivity of the SP44 antibody and its suitability for determining Met protein expression on FFPE tissue. Expression of Met was variable and heterogeneous in benign respiratory mucosa and pneumocytes. In a cohort of NSCLC patients (n=128) from a phase II trial evaluating MetMAb (onartuzumab), a one-armed anti-Met antibody, for the treatment of NSCLC, 54% of cases were classified as Met Dx+. A statistically significant benefit in progression-free (PFS) and overall survival (OS) was observed for patients with Met Dx+ tumors treated with the MetMAb antibody onartuzumab (PFS: Hazard ratio=0.53, 95% CI=0.28-0.99, p=0.04; OS: Hazard ratio=0.37, 95% CI=0.19-0.72, p=0.002.
Conclusions: We have characterized and validated an IHC assay for Met in FFPE tissues, which identifies a population of NSCLC patients who may derive benefit from Met-targeted antibody therapy with MetMAb (onartuzumab).
Tuesday, March 20, 2012 9:30 AM
Poster Session III # 302, Tuesday Morning