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There are two kinds of HER-2 test available to the laboratory, but one is
significantly more accurate than the other. One test is known as IHC (ImmunoHistoChemistry),
which measures the HER-2 protein present on the surface of the tumor cells.
There are two issues regarding the accuracy of this method:
* This protein can be damaged during certain preparation of the tissue sample
(the fixation and embedding in paraffin), causing variability in test outcome.
* Measurement is subjective (that is, a judgment call is required that is not
always accurate) and requires the greatest level of skill and expertise in its
interpretation by subjectively judging the degree of color against a
non-standardized chart.
PathVysion HER-2 uses Fluorescence in situ Hybridization, which measures the
HER-2 abnormality at the stable DNA level. The stability of DNA is well known.
The HER-2 DNA withstands the rigorous tissue processing that most breast cancer
tissue specimens must endure - a process which usually alters or destroys the
protein. Using the PathVysion HER-2 DNA FISH test the clinician counts the
actual number of HER-2 genes present in the cell nucleus, using a fluorescence
microscope. The count is objective (that is, no judgment is required - the
results are very clear) and tissue preparation has little effect on test
outcome.
In the opinion of breast cancer research pioneer and HER-2 specialist, Dr.
Dennis Slamon confirms the PathVysion HER-2 test outperformed other available
tests for HER-2 assessment. Dr. Slamon states, "In a head-to-head comparison
with other FDA-approved tests in our laboratory, the Vysis test was found to be
superior. In my opinion, it is the most reliable and accurate method of
assessing HER-2 status in breast cancer tissue specimens". According to Dr.
Slamon and other HER-2 researchers and clinicians, the best test for measuring
HER-2 status is one that directly quantifies the HER-2 gene, rather than
measuring the HER-2 protein that is over-expressed (overproduced).
"HER-2 protein over-expression in the absence of amplification rarely happens.
If you look at antibody-based tests that measure over-expression of the (HER-2)
protein in formalin-fixed, paraffin-embedded material, which is how the vast
majority of material comes to you (in the laboratory), the false negative rates
range from 15 to 20 percent - and that's with a good antibody reagent," explains
Dr. Slamon.
All in all, IHC has been shown, IHC has been shown, IHC has been shown to miss
15-20% of positive specimens, compared with less than about 5% with FISH
testing. PathVysion is the only HER-2 testing product to have three claims:
prognosis, type of chemotherapy selection and Herceptin® therapy selection. As
has already been stated, the key concept is: the most accurate HER-2 assessment
means the most accurate therapy decisions. PathVysion provides the most
accurate, reliable and objective means of assessing HER-2 status in breast
cancer.
Source :
http://www.pathvysion.com/BreastCancertests_272.asp