[Histonet] Re: Histonet Digest, Vol 25, Issue 9

From:John PJ Coleman

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.

JPJC-757 335-2159

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