Strong HER-2/neu protein overexpression by immunohistochemistry often does not predict oncogene amplification by fluorescence in situ hybridization.
Breast cancer patients with HER-2/neu oncogene amplification by fluorescence in situ hybridization (FISH) have been shown to have a better response to trastuzumab (Herceptin) therapy than those showing HER-2/neu protein overexpression only. Many centers currently perform FISH only on tumors showing 2+ HER-2/neu positivity by immunohistochemistry (IHC), with the assumption that 3+ positivity virtually equates with amplification. Results of FISH performed on 102 breast cancer cases over a 12-month period were correlated with HER-2/neu IHC results. FISH was performed using a ratio of HER-2/neu and chromosome 17 centromere signal counts (PathVysion; Vysis, Downers Grove, IL). Immunohistochemical expression of HER-2/neu was evaluated according to the published scoring guidelines of the HercepTest (Dako, Carpinteria, CA). Only 22 of 45 tumors with 3+ positivity (49%) showed amplification by FISH. Only 2 of 25 cases with 2+ staining by IHC (6%) showed gene amplification, and 1 of 25 cases with negative IHC staining (4%) showed weak amplification. Of the 25 cases showing oncogene amplification, 22 (88%) showed 3+ IHC positivity, 2 (8%) showed 2+ positivity, and 1 (4%) was negative by IHC. More than 50% of breast tumors showing strong 3+ HER-2/neu staining do not show oncogene amplification by FISH. Most tumors with 2+ and negative IHC also fail to amplify. In our experience, FISH studies should be performed on all 3+ and 2+ staining tumors to avoid inappropriate and toxic treatment. The decision to perform FISH on IHC-negative tumors should be guided by additional parameters, including tumor grade and estrogen receptor status.
Hammock
Lauren
L
Department of Pathology and Laboratory Medicine, Emory University Hospital, Atlanta, GA, USA.
Lewis
Melinda
M
Phillips
Carol
C
Cohen
Cynthia
C
D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism* / Q000556:secondary; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D005260:Female; D005784:Gene Amplification; D018734:Genes, erbB-2; D006801:Humans; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence; D011933:Reagent Kits, Diagnostic; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*
D011933:Reagent Kits, Diagnostic; D018719:Erb-b2 Receptor Tyrosine Kinases