[Histonet] Underfixation of breast tissue may lead to false results?

Bryan Llewellyn llewllew <@t> shaw.ca
Wed Mar 23 12:28:08 CDT 2011

This has been commented on several times by old fogey histotechs in the 

Any formalin variant takes some time to actually chemically alter (fix) 
the tissue.  Usually this is a minimum of 24 hours for a 3-4 mm thick 
piece.  In modern labs there is a focus on 24 hour or less turnaround 
time, so formalin fixation is usually minimalist and may be inadequate, 
as in this case.  After all, the universe will not change itself for our 
benefit just because we want fast results.

This means that underfixed tissues with just a few hours in formalin are 
processed.  The unfixed components are exposed to ethanol during this 
process.  Remember that ethanol is also a (very poor) fixing agent, so 
the inadequatly fixed tissue is fixed by it, with all the 
characteristics ethanol fixation gives, shattering, hardening, 
distortion, etc. This is frequently referred to as "overprocessing", but 
it is just poor fixation from ethanol. For most tissues, wetting the 
block surface allows reasonable sections to be cut, but that is only a 
quick fix.

Procedures which require tissues to be properly fixed may not be 
successful as a consequence.

Bryan Llewellyn

Goodwin, Diana wrote:
> Dear Histonetters:
> I recently read the following in an article on Medscape:
> "Underfixation of breast tissue may lead to false negative ER results and false-positive HER2 results.  In these situations, the tissue is actually fixed in 100% ethanol, which is used to dehydrate the specimens after fixation."
> Can anyone explain?
> Diana Goodwin
> Supervisor, Histology Laboratory
> xt. 6996
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