Testing for HER-2 oncogene in breast cancer has increased because of
its role as a prognostic and predictive factor. Some advocate gene testing
by fluorescence in situ hybridization (FISH) vs protein testing by immunohistochemistry
as the method which most accurately evaluates and predicts response to the
anti–HER-2 antibody, trastuzumab. However, critical examination of FISH
on a screening basis has yet to be performed.
To determine the correlation between FISH and immunohistochemistry results
by determining HER-2/neu gene status on tumor sections
with indeterminate immunohistochemistry results (2+ score), confirm gene amplification
on tumor sections with positive results (3+ score), and verify gene status
on tumor sections with negative results (0 or 1+ score).
Design, Setting, and Patients
A quality control and quality assurance program for HER-2 testing by
FISH, which used tumor specimens from 2963 patients (median age, 56 years)
with breast cancer received from 135 hospitals and cancer centers in 29 states,
was performed at a reference laboratory from January 1, 1999, to May 15, 2003.
Every specimen evaluated by FISH was parallel tested with immunohistochemistry
Main Outcome Measures
With FISH as the presumed standard testing method, the positive and
negative predictive values and sensitivity and specificity of immunohistochemistry
A total of 3260 clinical HER-2 tests by FISH were performed on 2963
serially referred breast cancer specimens. Of these, 2933 tests were successful
and 2913 breast cancer specimens had both FISH and immunohistochemistry results
available. With FISH as the standard testing method, the positive predictive
value of positive immunohistochemistry score (3+) was 91.6%, and the negative
predictive value of negative immunohistochemistry score (0 or 1+) was 97.2%.
The sensitivity of immunohistochemistry tests, including tumor sections with
scores of 2+ or 3+, was 92.6% and the specificity of immunohistochemistry
tests with scores of 3+ was 98.8%. The FISH test had a significantly higher
failure rate (5% vs 0.08%) and reagent cost ($140 vs $10), and longer testing
(36 hours vs 4 hours) and interpretation times (7 minutes vs 45 seconds) vs
A testing algorithm for HER-2 determination is most efficient by using
immunohistochemistry as the method of choice, with FISH performed for cancers
with indeterminate results (2+ score). Successful quality control and quality
assurance programs are a prerequisite for such approaches.