Abstract
I was interested to read the paper by Farra and colleagues published in the October 2019 issue of Clinical Breast Cancer. 1 Farra C. Fedda F. Tfayli A. et al. The impact of partial weak staining in normal breast epithelium on the reliability of immunohistochemistry results in HercepTest-positive breast cancer. Clin Breast Cancer. 2019; 19: 340-344 Abstract Full Text Full Text PDF PubMed Scopus (3) Google Scholar Normal epithelial cells do not show human epidermal growth factor receptor-2 (HER2) gene amplification and should lack membrane staining by HER2 immunohistochemistry (IHC); but HER2 staining in benign breast epithelium is occasionally encountered. The authors aimed to assess the correlation between HER2 IHC 3+ cases of breast cancer with normal epithelium staining (NES) and their corresponding fluorescence in situ hybridization (FISH) results, and to suggest recommendations for interpretation. They reviewed 154 cases of breast cancer with HER2 IHC 3+. NES was scored as present or absent. All study cases were sent for FISH testing. All cases, and particularly those that showed false positivity for IHC (positive IHC, negative FISH), were examined for NES. They reported that of the 154 cases, 146 cases were FISH-positive (94.8%) and 2 failed FISH testing (1.3%). Conversely, 22% (34/154) of the cases showed NES for HER2. Of these 34 cases, 23 (67%) were FISH-amplified, 9 (26%) were FISH not amplified, and 2 failed FISH testing. Notably, all of the false-positive (FISH-negative) cases of breast cancer showed some degree of positivity in normal breast epithelium.
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