Determining sensitivity and specificity of HER2 testing in breast cancer using a tissue micro-array approach.
BACKGROUND
Overexpression of the human epidermal growth factor receptor 2 (HER2) as a result of HER2 gene amplification is associated with a relatively poor prognosis in breast cancer and is predictive of HER2-targeting therapy response. False-positive rates of up to 20% for HER2 testing have been described. HER2-testing laboratories are therefore encouraged to participate in external quality control schemes in order to improve HER2-testing standardization.


METHODS
This study investigated the feasibility of retesting large numbers of invasive breast cancers for HER2 status on tissue micro-array (TMA) as part of a quality control scheme. For this assessment different HER2 testing methods were used including HER2 detecting antibodies SP3, 4B5, Herceptest and mono color silver in situ hybridization (SISH) and dual color SISH. Final HER2 status for each tumor on the TMA was compared to the local testing result for the same tumor. Discordances between these two results were investigated further by staining whole tumor sections.


RESULTS
For this study, 1,210 invasive breast carcinomas of patients treated in six hospitals between 2006 and 2008 were evaluated. Results from the three immunohistochemistry (IHC) and two in situ hybridization (ISH) assays performed on the TMAs were compared. The final HER2 status on TMA was determined with SP3, 4B5 and mono color SISH. Concordance between local HER2 test results and TMA retesting was 98.0%. Discordant results between local and TMA retesting were found in 20 tumors (2.0%). False positive HER2 IHC results were identified in 13 (1.3%) tumors; false negative IHC results in seven (0.7%) tumors.


CONCLUSIONS
Retesting large volumes of HER2 classified breast carcinomas was found to be feasible and can be reliably performed by staining TMAs with SP3, 4B5 and mono color SISH in combination with full-sized slides for discordant cases. The frequency of false-positive results was lower than previously reported in the literature. This method is now offered to other HER2-testing laboratories.
Department of Pathology, Academic Medical Center, Meibergdreef 9, Amsterdam, 1100 DD, The Netherlands.
Tim J A
TJ
Dekker
Susan Ter
ST
Borg
Gerrit K J
GK
Hooijer
Sybren L
SL
Meijer
Jelle
J
Wesseling
James E
JE
Boers
Ed
E
Schuuring
Jos
J
Bart
Joost
J
van Gorp
Wilma E
WE
Mesker
Judith R
JR
Kroep
Vincent T H B M
VT
Smit
Marc J
MJ
van de Vijver
D000951:Antigens, Neoplasm / Q000032:analysis / Q000276:immunology; D014408:Biomarkers, Tumor / Q000032:analysis; D001943:Breast Neoplasms / Q000175:diagnosis*; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D011786:Quality Control; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis* / Q000276:immunology; D012680:Sensitivity and Specificity; D046888:Tissue Array Analysis
D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor; D018719:Erb-b2 Receptor Tyrosine Kinases; C076519:4B5 antigen; C508053:ERBB2 protein, human