Assessment of HER2 gene amplification in adenocarcinomas of the stomach or gastroesophageal junction in the INT-0116/SWOG9008 clinical trial.

4010 Background: Trastuzumab has been approved for treatment of patients with HER2-positive metastatic gastric carcinoma; however, relatively little is known about the role of HER2 in the natural history of this disease. Methods: Patients enrolled in the INT-0116/SWOG9008 phase III gastric cancer clinical trial (n=559) were retrospectively evaluated for HER2 gene amplification by fluorescence in situ hybridization (FISH)(n=258), overexpression by immunohistochemistry (IHC)(n=148) and HER2 amplification by silver-enhanced in situ hybridization (n=77) based on availability of tissue specimens. The purpose of the original clinical trial was to evaluate the benefit of post-operative 5-fluorouracil/leucovorin plus radiation therapy compared to surgery alone. Results: HER2 gene amplification rate by FISH was 10.9% in tumor tissue from 258 patients evaluated. HER2 status determined by FISH was 92% concordant with SISH. HER2 overexpression rate by IHC was 12.2% among 148 patients evaluated, with 90% agreement bet...