ERBB2 and neoplasm: To test the above-mentioned hypotheses, we (a) quantified HER2-positive tumor cells in six different regions in gastric resection specimens to measure the spatial HER2 expression heterogeneity and (b) assessed HER2 expression status in six virtual biopsy specimens from different luminal locations within the tumor to calculate the concordance rate between biopsy specimen and resection specimen HER2 status.