Breast cancers presenting luminal B subtype features show higher discordant human epidermal growth factor receptor 2 results between immunohistochemistry and fluorescence in situ hybridization

Abstract

The aims of this study were to compare human epidermal growth factor receptor 2 (HER2) results between immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH), and to investigate the clinicopathological characteristics and outcomes according to their results. Using consecutive tissue microarrays, IHC and FISH were performed as guidelines in 950 invasive breast cancers treated between November 1999 and August 2005. Characteristics and outcomes were retrospectively analyzed using a chi-square test, the Kaplan-Meier method, and Cox's model. FISH-positivity was observed in 2.6%, 4.8%, 28.1%, and 93.8% of IHC 0, 1+, 2+, and 3+, respectively, and the concordance rate between the 2 assays was 95.5%. IHC-positive or FISH-positive cases were associated with poorer differentiation, negative expression of hormone receptors, and higher proliferative index. Among IHC-equivocal or IHC-negative patients, positive FISH was negatively associated with survival in univariate and multivariate analyses. Among IHC-negative patients, tumors showing luminal B subtype features such as estrogen receptor (ER)-positive, grade II/III, and high Ki-67 presented discordantly high FISH-positivity. Among IHC-positive cases, FISH was not related to outcomes. The result of FISH is significantly related to prognosis of patients with IHC-negative or IHC-equivocal result. Therefore, FISH should be performed in IHC-equivocal cases. FISH assay might be considered for a selected group of patients with IHC-negative tumors showing luminal B subtype features of ER-positive, grade II/III, and high Ki-67 expression.