Assessing HER-2/Neu Protein Expression and Gene Alteration in Gastric Cancer: Comparing Arrayed Comparative Genomic Hybridization (aCGH) Technique with Immunohistochemistry (IHC) and Fluorescent In-Situ Hybridization (FISH)
CD Truong, W Feng, W Li, T Khoury, J Yao, K Xie, D Tan. The University of Texas MD Anderson Cancer Center, Houston, TX
Background: Inconsistent results for HER-2/neu expression (at the protein or gene level) in gastric cancer using IHC and FISH and Herceptin's promising role in the treatment of gastric cancer have been reported in several studies. These inconsistencies may partially be due to variation in evaluation techniques and/or heterogeneity of the populations studied. The objective of this study was to assess HER-2/neu expression using aCGH in a well-defined large cohort of gastric cancer patients, and to compare this novel technique with the traditional approaches of IHC and FISH under uniform test conditions.
Design: Tissue samples from 200 patients with primary gastric cancer were evaluated by IHC analysis (using an FDA-approved Hercept monoclonal antibody kit) and FISH with standard score criteria used for both methods. Among this cohort, 43 cases had adequate tissue for assessing DNA copy number changes by oligonucleotide aCGH (244K, Agilent). For each aCGH probe, each sample was classified as having normal, gained, or lost DNA copy number based on log 2 ratio thresholds of 0.15.
Results: Twenty patients (10%) overexpressed (2+, 3+) HER-2/neu protein, while 90% showed negative (0, 1+) expression. Eighteen patients (9%) displayed HER-2/neu gene amplification by FISH. Although HER-2/neu protein overexpression was found to correlate well with HER-2/neu gene amplification (r=0.83, p<0.01), we found discordances in 3 cases. One case with negative (1+ by IHC) expression showed HER-2/neu amplification by FISH. Two cases with overexpression (2+ by IHC) did not show HER-2/neu amplification by FISH. On the other hand, aCGH detected HER-2/neu amplification in 16% of cases, of which 3 cases were negative by IHC and FISH. In addition to identifying HER-2/neu gene amplification, aCGH also displayed abnormalities of other associated critical genes, such as DACT3, DKKL1, EGFR, EMP3, HIF3A, HRC, IGFL2, IGFL3, KPTN, LIG1, and PNKP, many of which have been implied in the carcinogenesis of solid tumor including gastric cancer.
Conclusions: Although IHC and FISH offer direct in-situ assessment of molecular changes within the cells of interests, genome wide aCGH is more superior. In addition to having higher sensitivity in detecting HER-2/neu gene amplification, aCGH can also reveal a panel of associated gene changes, which may be more beneficial in personalizing treatment using multi-target therapy.
Monday, March 9, 2009 9:30 AM
Poster Session I Stowell-Orbison/Autopsy Award # 247, Monday Morning