Association of real-world agreement between HER2 expression and ERBB2 amplification with trastuzumab therapy benefit in advanced gastric/esophageal (adv GE) cancer patients (pts).

310 Background: Trastuzumab (T) plus chemotherapy is standard of care for pts with HER2+ adv GE cancer. Selection for T relies on HER2+ result by immunohistochemistry (IHC) +/- in-situ hybridization (ISH); ERBB2 amplification by comprehensive genomic profiling (CGP) also predicts benefit. As CGP use increases, it is important to explore associations of IHC/ISH and CGP result agreement with clinical outcomes in pts with adv GE cancer. Methods:...