HercepTest is a semi-quantitative immunohistochemical assay for determination of HER2 protien (c-erbB-2 oncoprotein) overexpression in breast cancer tissues routinely processed for histological evaluation and formalin-fixed, paraffin-embedded cancer tissue from patients with adenocarcinoma of the stomach, including the gastroesophageal junction. Hercep Test specifically demonstrates overexpression of HER2 protein.