Analysis of IGF1R gene copy number by silver in situ hybridization (SISH) in non-small cell lung cancer (NSCLC)

Abstract

7525 Background: IGF1R is a potential biomarker for predicting outcome of NSCLC patients (pts) treated with therapeutics targeting the IGF1R signaling pathway. SISH can be expeditiously analyzed on a bright field microscope given that the morphology of the tissue is observed concurrent to the scoring of discrete gene signals. Methods: An experimental SISH probe designed by Ventana Medical Systems (Tucson, AZ) was used to evaluate IGF1R gene copy number on a tissue microarray containing triplicate samples from 189 pts surgically treated for NSCLC (median follow-up 4 years and 5-year survival probability of 40%). Valid results, at least one core with sufficient tumor content for assessment, were obtained for 166 patients. There were 128 males; 93 squamous cell carcinomas (SCC), 47 adenocarcinomas, 5 large cell carcinomas and 21 other histologies. The pathological stages were I: 68, II: 37 and III/IV: 60. The mean number of IGF1R gene copies/nuclei/core was determined by a board certified pathologist counting 50 nuclei in each core. The mean number of IGF1R gene copies/nuclei/patient was determined by using, within the triplicates, the core with the highest gene copy number/nuclei. Results: The mean number of IGF1R gene copies/nuclei per patient was 2.26 (range: 1.12 - 7.56; standard deviation 0.81). The median copy number was 2.11. The pts were divided into two groups, those with 2.1 genes/nuclei or less and those with greater than 2.1 genes/nuclei. There was no statistical difference related to gender (p=0.422) or between pathological stages, (p=0.221). However, there was a highly significant difference between the two categories when considering histological pattern. Among patients with SCC, 66.3% had high copy number compared to 33.7 % in non-SCC histologies (p=0.008). Analysis of overall survival comparing pts with low vs. high IGF1R gene copy number revealed no statistical difference in the median survival: 1.5 yrs (95% CI 0–3.7 yrs) vs. 3.3 yrs (2.0–4.5 yrs) or the 3-year survival: 46% (35–57%) vs. 52% (41–63%). Conclusions: IGF1R gene copy number detected by SISH is higher in SCC than in other histologies of NSCLC, but does not associate with gender, pathological stage or survival. IGF1R SISH should be further explored as a predictive biomarker for IGF1R therapeutics. [Table: see text]