Does a change from IHC to FISH enhance patient selection for HER2 therapy?

Abstract

e11015 Background: Breast cancer is the most commonly diagnosed malignancy among women in the United States. Among various subtypes of breast cancer, tumors that overexpress the human epidermal growth factor receptor 2 (HER2) have an aggressive biology. The frequency of HER2 gene amplification is about 20% among breast cancer patients. The diagnostic tests to determine HER2 status in breast cancer include Immunohistochemisty (IHC), and Fluorescence In-Situ Hybridization (FISH). The interpretation of IHC is subjective and may depend on the pathologist. It is unknown whether the use of FISH has led to higher detection of HER2 overexpression. Methods: We conducted a retrospective review of patients diagnosed with breast cancer from 2000 to 2008. A total of 865 breast cancer patients were reviewed. One hundred and sixty five (19%) were diagnosed with HER2+ subtype. Our institution utilized IHC (HER2-pY 1248 antibody, Dako Corporation) from 2000 to 2003 and FISH (Path Vysion, HER-2 DNA Probe Kit) from 2004 to 2008. Results: The frequency of HER2 detection in breast cancer by IHC from 2000-2003 was 17%. The detection by FISH from 2004-2008 was 20%, an increase of 3%. Conclusions: We observed an increase in the diagnosis of HER2+ breast cancer with the introduction of FISH. This modest difference when applied to a large group of patients could translate into more patients being eligible for anti-HER2 therapy and may enhance accrual to clinical trials.