HER2 status of gastric carcinoma and corresponding lymph node metastasis

Our goal is to verify HER2 status variability between primary tumor and metastatic site. Our second intention is to identify the most reliable criteria for pathological HER2 status assessment in gastric cancer node metastases since, at present, there is not a validated standard. 3 independent pathologists evaluated HER2 immunohistochemical and gene status (for IHC 2+ cases) in 34 gastric carcinoma metastatic lymph nodes and in their corresponding primary tumors. For primary gastric cancers, we followed the current HER2 assessment guidelines and for nodal metastases, we applied two immunohistochemical scoring systems with different cut-offs. The immunohistochemical inter-pathologists mean agreement was 71.4 % (κ = 0.45); a final score for each case was defined after collegial revision. By applying the two immunohistochemical criteria, we found 2 discordant cases, which can imply different pathological management. Moreover, a significantly different HER2 status between lymph node metastasis and primary tumor was obtained in 4 cases (concordance ratio 87.5 %). None of the patients would have undergone a different therapeutic pathway despite the scoring method applied. On the other hand we also detected a subset of patients who could have their therapeutic management changed, according to the differences between HER2 status in lymph nodes metastases and primary tumor.