[Histonet] Re: Histonet Digest, Vol 25, Issue 9
John PJ Coleman
jcolclefa <@t> aol.com
Wed Dec 7 21:10:54 CST 2005
Her2 by fish and her 2 by IHC like in Dako Herceptest are not testing
for the same item. Fish lights up the genes, IHC labels the cell
surface proteins. Herceptin is a drug based on surface expression of
protein, not presence of multiple gene copies. The assumption by Vysis
( the FISH pushers) is that multiple gene copies = protein presence at
cell surface and that IHC labs are not competent. What if the fish is
called negative because of a 1:1 ratio but that multiple copies of gene
and centromere are present within a set of cells that are 3+ according
to IHC because of accelerated protein production? Deny therapy in a
potentially responsive patient? But I digress. Herceptest is not
recommended for core biopsies- i run i high volume IHC lab (518 slides
yesterday) and we found that core bxs score higher by IHC than average.
We also do FISH weekly, and we have found that 1+ ihc= always neg fish,
2+ ihc = 96% or so Neg fish, and 3+ = 85 or so pos fish. What
specifically are your issues with the cores?
like I said - we get potentially higher IHC +, fish neg on cores.
Also- in IHC negative controls are used to tell if the secondary
reagents are causing a chromogenic reaction on the slides independent
of the primary antibody. Really has nothing to do with the varying
intensity of the reaction in the test slides. It's just to avoid
reporting out a false positive result.
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