[Gastric cancer genome profiling reveals HER2 false-negative status and informs a successful trastuzumab treatment...

Intratumoral HER2 heterogeneity is a well-described gastric cancer feature and may explain many false-negative results related to this oncogene. An 81-year-old man was diagnosed at our hospital with stage IV gastric cancer with multiple lymph node metastases. Immunohistochemistry (IHC) analysis indicated that the primary tumor was HER2-negative. After a chemotherapy course, we submitted a pretreatment biopsy specimen for comprehensive cancer genome profiling (CGP) to determine the last-line therapy. This revealed HER2 amplification. The specimen was reevaluated using fluorescence in situ hybridization and IHC with deeper-cut specimens, which confirmed that the tumor was indeed HER2-positive. Therefore, the patient was treated with chemotherapy plus trastuzumab, which elicited tumor shrinkage and conferred long-term survival. Our current data underscore the CGP importance, which can provide more accurate tumor profilings and inform subsequent treatment decisions.