Impact of Specimen Type and Specimen Number on HER2 Status in Gastroesophageal Junction and Gastric Adenocarcinoma.

Abstract

Human epidermal growth factor receptor 2 (HER2) is expressed in some gastric and gastroesophageal junction adenocarcinomas. There were two goals: assess the impact of specimen type on HER2 status and evaluate HER2 concordance with multiple specimens. All cases were evaluated by immunohistochemistry (IHC) for HER2 and interpreted using established criteria. Fluorescence in situ hybridization (FISH) was performed on a subset. Of 460 specimens, 83.9% were IHC negative, 5.4% were equivocal, and 10.7% were IHC positive. Of those with FISH testing, 78.5% were FISH negative, and 21.5% were FISH positive. IHC-FISH concordance for biopsy specimens, resections, and metastases was 82%, 84%, and 86%, respectively. With one vs two vs three or more specimens, the HER2-positive rate increased from 10.5% to 18.1% to 24.1%, respectively. HER2 testing may be performed on biopsy specimens with a relatively high concordance rate with resection specimens, and if multiple samples are analyzed from a single patient, the HER2-positive rate increases over twofold.