HER2 testing in patients with breast cancer: poor correlation between weak positivity by immunohistochemistry and gene amplification by fluorescence in situ hybridization.
OBJECTIVE
To evaluate amplification of the HER-2/neu gene by fluorescence ir situ hybridization (FISH) in tumors with weakly positive (2+) immunohistochemical staining.


METHODS
A total of 1556 breast tumor biopsy specimens were referred to Mayo Medical Laboratories, Rochester, Minn, for HER2 testing between August and December 2000. Immunohistochemical (IHC) analysis was performed with use of a diagnostic test for the assessment of HER2 overexpression, the HercepTest. The IHC-stained slides were interpreted and scored on a scale ranging from 0 to 3+ according to Food and Drug Administration-approved guidelines. All specimens scored as 2+ were also routinely evaluated by FISH with use of a HER-2/neu DNA probe kit (PathVysion). Specimens were determined to be amplified if the ratio of HER-2/neu signals to chromosome 17 centromere (CEP17) signals was higher than 2.0.


RESULTS
Thirty-eight percent of the specimens evaluated with the HercepTest were scored 0, 35% were 1+, 14% were 2+, and 13% were 3+. Of the 216 tumor specimens scored as 2+, 26 (12%) had a high level of HER-2/neu gene amplification, 54 (25%) demonstrated duplication of HER2, 4 (2%) deleted HER-2/neu and/or CEP17, and 123 (57%) had no apparent HER-2/neu anomaly, no apparent CEP17 anomaly, nor apparent single gain (aneusomy) of CEP17.


CONCLUSIONS
We recommend that all specimens with a 2+ HercepTest result be evaluated by FISH for HER-2/neu gene amplification. The results of both assays should be considered before making a decision to recommend anti-HER2 therapy.
Perez
Edith A
EA
Division of Hematology/Oncology, Mayo Clinic, Jacksonville, FL 32224, USA.
Roche
Patrick C
PC
Jenkins
Robert B
RB
Reynolds
Carol A
CA
Halling
Kevin C
KC
Ingle
James N
JN
Wold
Lester E
LE
D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D061067:Antibodies, Monoclonal, Humanized; D001706:Biopsy; D001943:Breast Neoplasms / Q000145:classification / Q000235:genetics* / Q000473:pathology / Q000628:therapy; D002503:Centromere / Q000235:genetics; D002869:Chromosome Aberrations / Q000145:classification; D002872:Chromosome Deletion; D002886:Chromosomes, Human, Pair 17 / Q000235:genetics; D003362:Cost-Benefit Analysis; D005260:Female; D005784:Gene Amplification; D020440:Gene Duplication; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D018734:Genes, erbB-2 / Q000235:genetics*; D006801:Humans; D007120:Immunochemistry / Q000191:economics / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D017404:In Situ Hybridization, Fluorescence / Q000191:economics / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D009367:Neoplasm Staging / Q000379:methods / Q000592:standards; D021141:Nucleic Acid Amplification Techniques; D018579:Patient Selection; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D000068878:Trastuzumab; D016896:Treatment Outcome
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000068878:Trastuzumab