Differential HER2 expression in resected gastric cancer: Is there prognostic value?

Abstract

54 Background: For advanced gastric cancer, the ToGA trial established HER2 as an important therapeutic target in the 20% of patients whose tumors exhibited HER2 overexpression or gene amplification. Others have reported that HER2-positive tumors are associated with poor survival in advanced disease. The expression profile and prognostic value of HER2 in resectable gastric cancer are unknown. Methods: 111 pts underwent curative intent resection of gastric adenocarcinoma between 1/00-6/11 and had tissue available for analysis. Immunohistochemistry (IHC) for HER2 was performed on banked tumor specimens and graded by two pathologists blinded to outcomes utilizing ToGA trial criteria. An IHC score of 0+ or 1+ was regarded as negative, 3+ as positive. Fluorescence in-situ hybridization (FISH) for HER2 was performed on equivocal (2+) IHC samples. Primary outcome was differential expression, secondary outcome was overall survival (OS). Results: Median age was 64 years, 54% were male. Median tumor size was 4 cm, 7.2% had a positive margin, 67.6% were poorly differentiated, 23.4% had perineural invasion, 35.1% had lymphovascular invasion, and 61.3% had nodal metastases. 24 patients had stage I disease (21.6%), 32 stage II (28.8%), and 55 stage III (49.6%). Mean follow-up was 28.9 months, median OS was 27.2 months. HER2 expression by IHC was negative in 61 (55%), equivocal in 37 (33.3%), and positive in 13 (11.7%). Of the 37 equivocal cases, FISH was positive in 8, for a total of 21 HER2-positive cases (18.9%) and 90 HER2-negative cases (81.1%). HER2 status did not correlate with T or N stage, tumor size or location, tumor grade, or perineural or lymphovascular invasion. HER2 status was not associated with OS (p=0.36). Conclusions: Resectable gastric cancer exhibits differential expression of HER2, similar to that of advanced disease. Despite reports suggesting HER2 positive status is associated with aggressive disease and worse outcomes in the advanced setting, HER2 status is not associated with adverse pathologic factors or survival in resectable disease. Although not prognostic, the predictive value of HER2 status for response to trastuzumab in the adjuvant setting requires further investigation.