Not if you set the instrument to start EXACTLY when you want. You will have the tissues in melted paraffin more time, or you can extend the dehydration times. You can do a lot of things all preventing longer fixation in NBF. Modern TP are very flexible instruments and I have no data that reflects any deleterious effects for the tissues' reactive qualities or sectioning characteristics after being in melted paraffin for long periods of time.
I agree with Rich, and it's good to hear that some colleagues have
started their own mode of cross-validation.
If you choose to deviate from the upper fixation limit of 48 hours,
you will ONLY be at default if you do not have evidence (with
documentation) that raising the upper fixation limits to 72 or 96
hours has no detrimental effects on the results. The CAP will
eventually increase the upper limit to 72 (or hopefully 96) hours once
there is solid evidence that is ok to do so.
Rene's suggestion to put the instrument on delay is not a valid
solution. As long as the tissue is sitting in formalin in the
instrument while it's on delay, it's still being fixed. This issue was
discussed at the ASCO/CAP meeting.
Hadi Yaziji, M.D., Medical Director
Vitro Molecular Laboratories,
President, Ancillary Pathways
7000 SW 62nd Avenue, Suite Penthouse-C
Miami, FL 33143
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Date: Thu, 24 Jan 2008 09:57:05 -0500
From: "Richard Cartun"
Subject: Re: [Histonet] HER2neu Fixation times
To: "Ramona Turner" ,
Content-Type: text/plain; charset=US-ASCII
Personally, I would not initiate any drastic changes at this point.
Keep in mind that these are guidelines; however, you must validate
your testing if you are going to follow other fixation guidelines. I
think everyone knowledgeable with this issue knows that the problem is
with underfixation, not overfixation. I recently pulled tumor out of
formalin after 8 months of fixation and the IHC was still "3+" and the
FISH showed beautiful amplification (ratio of 10.0). I hope that once
the scientific evidence is evaluated, these guidelines will be
changed. Major expense is being incurred here unnecessarily. How is
your concordance between IHC and FISH for the detection of HER2? If
it's not broken, don't try to fix it. Our "ad-hoc" committee on IHC
standardization is meeting in Santa Barbara on Sunday and I hope this
issue will be discussed.
Richard W. Cartun, Ph.D.
Director, Immunopathology & Histology
Assistant Director, Anatomic Pathology
80 Seymour Street
Hartford, CT 06102
(860) 545-0174 Fax
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