The present study evaluated HER2 status between primary gastric and paired metastatic disease to lymph nodes, collecting 62 formalin-fixed paraffin-embedded representative tissue blocks as well as synchronous metastatic lymph nodes by immunohistochemistry and FISH. The discordant HER2 pooled rate, regardless either negative or positive conversion, was 9.26% in primary gastric carcinoma and corresponding nodal metastasis. Moreover, a high level concordance in HER2 expression between primary carcinoma and synchronous metastatic lymph nodes was achieved in 90.74% of cases. In our opinion, the observed event of discordant HER2 status should be ascribed to intra-tumor heterogeneity. In any case, the shift from positive to negative HER2 expression suggests that Trastuzumab could be the targeted treatment choice, while the opposite shift should be evaluated by a simultaneous HER2 determination in both primary and metastatic lymph nodes
