Background: Recent advances in molecular targeted therapy have identified HER2 as an important target for anti-cancer therapy in gastric cancer (GC). Although the clinical relevance and prognostic significance of HER2 in breast cancer has been well acknowledged, it remains controversial in GC.
Methods: HER2 expression was investigated in two independent series of GC by immunohistochemical staining. One series corresponded to 1,414 cases of whole-tissue sections and the other corresponded to 595 cases of tissue microarrays (TMAs). Results were compared and correlated with clinicopathologic parameters.
Results: HER2-positivity was detected in 12.3% of whole-tissue sections and 17% of TMAs. Among samples scored 3+, 90.1% stained ≥50% of the tumor area, but only 40.9% in score 2+ cases stained ≥50% of the tumor area. In whole-tissue sections, HER2-positivity was correlated with age (P = 0.002), histological type (differentiated or intestinal, P < 0.001), lymphovascular invasion (P = 0.005), and lymph node metastasis (P = 0.009). In TMAs, HER2-positivity was correlated only with age (P = 0.003) and histological type (P < 0.001). Multivariate analyses of the differentiated GC subgroup revealed that HER2-positivity was an independent poor prognostic factor (P = 0.042). The cases with HER2-positive in ≥50% of the tumor area showed worse prognosis than those of <50% (P = 0.021).
Conclusions: Despite discrepancies in the results from whole-tissue sections and TMAs, HER2 overexpression was positively correlated with aggressive biological behavior and was an independent poor prognostic factor for recurrence in differentiated GCs. Therefore, HER2-positive GCs should be considered for adjuvant trastuzumab therapy.