The Assessment of HER2 Gene Status by Fluorescence In Situ Hybridization in Invasive Breast Carcinomas With Equivocal HER2 Immunostaining: Experience From a Single Institution.

Background: A subset of breast carcinomas harbors overexpression of the human epidermal growth factor receptor 2 (HER2). Fluorescence in situ hybridization (FISH) should be performed in breast carcinomas with equivocal HER2 immunostaining (immunohistochemistry [IHC] HER2 2+). The aim of our study is to investigate clinicopathologic factors associated with HER2 status in breast invasive carcinomas with IHC HER2 2+ through FISH analysis.

Methods: This is a retrospective study including the FISH analysis of 111 patients with invasive breast carcinomas with equivocal HER2 immunostaining.

Results: The mean age was 49.51 ± 10.48 years, and invasive breast carcinoma of no special type was the most histological type in our study (96.4%). Most patients had tumors positive for hormones receptors (88.2% positive for estrogen receptor and 81.4% for progesterone receptor). On FISH, the HER2 amplification rate was 22.5%. There was no significant association of HER2 status with any clinicopathologic factors ( P > .05).

Conclusions: Our study shows that there are no reliable clinicopathologic factors to predict the HER2 status in breast tumors with equivocal HER2 immunostaining, supporting the necessary usage of FISH in such circumstances.