Background: c‐Met is a receptor capable of activating downstream proliferative, survival and invasive pathways. Numerous human malignancies, including NSCLC, show over‐expressed and amplified c‐Met. Elevated expression of c‐Met and its ligand, HGF, have been associated with inferior prognosis. The aim of this study was to evaluate the prognostic relationship of c‐Met gene copy number in surgically‐treated NSCLC patients (pts) using dual‐color silver in situ hybridization. SISH is advantageous because bright field microscopy allows visualization of intact malignant and non‐malignant cell morphology.

Methods: Experimental SISH probes, Ventana Medical Systems, Inc. (Tucson, AZ), were used to evaluate c‐MET and CH 7 copy numbers on a tissue microarray containing triplicate samples from 189 pts (median follow‐up 5.3 yrs and 5‐yr survival probability 38%). Evaluable results, at least one core with valid c‐Met and CH 7 counts, were obtained for 140 pts. There were 109 males; 80 squamous cell carcinomas; and 37 adenocarcinomas. The pathological stages were I: 50, II: 33 and III: 46, IV: 8 and unknown: 3. A certified pathologist counted signals (1 for individual signal, 6 for small cluster and 12 for big cluster) in 50 nuclei for each core and the mean number of c‐Met and CH 7 copies/nucleus/core were determined, along with the ratio. The triplicate cores were averaged and compared to the core with the highest score.

Results: There was very high correlation between the highest core and the average of the triplicate cores: c‐Met (r=0.98), CH 7 (r=0.96), and ratio (r=0.98). The highest core value was used for further analysis. The median copy numbers were: c‐Met 3.1 (1.7–11.8), CH7 2.4 (1.5–2.4), and ratio 1.3 (0.6–6.3). There were 14 pts with greater than or equal to five c‐Met genes/nucleus and 3 pts with clusters. Using the median as a cut‐off there was no statistical difference related to age, gender, pathological stage, histology, grade or smoking. Kaplan‐Meier analysis revealed no significant differences in PFS or OS using the median scores, however there was a trend for increased PFS and OS in patients with high copy numbers. Cox regression analysis examining copy number as a continuous variable, and accounting for other variables, showed a similar trend of protection but statistical significance was not achieved: c‐Met (PFS‐ HR 0.88 (0.72–1.07, p=0.19, OS‐ HR 0.90 (0.73–1.10), p=0.29); CH7 (PFS‐ HR 0.88 (0.57–1.34, p=0.54, OS‐ HR 1.02 (0.66–1.57), p=0.95): ratio (PFS‐ HR 0.84 (0.54–1.30, p=0.43, OS‐ HR 0.79 (0.49–1.28), p=0.33). Analysis of the data using a cut‐off of 5 for c‐Met gave similar results.

Conclusions: This study shows the clinical feasibility of SISH technology for c‐Met gene copy number assessment. There was a trend for increased PFS and OS in pts with increased c‐Met, CH 7 or the ratio between the two. Further studies are needed to determine the predictive value of c‐Met gene copy number in pts receiving molecular targeted therapeutics.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B45.