Tissue microarrays (TMA) are a
proven method, whereby tissue samples from multiple
patients can be arrayed onto a single paraffin block.
Using a small needle to biopsy standard histologic
blocks, cores from multiple conventional blocks are
transferred to a single block in array format. By
arraying the diverse samples in this manner, a high
throughput approach can be applied to the analysis
of tissue samples.
The manifold success of molecular
biology techniques enabled the indentification of
numerous novel biomarkers. These proteins hold great
promise as therapeutically useful determinants in
the process of diagnosis and prognosis. However, traditional
histopathological techniques have proven far too costly
and labor-intensive for their use as a timely approach
to the analysis of multiple samples. However, with
the application of TMA, a high throughput approach
is now possible. Fast and efficient analysis of over
1000 tissue samples can performed simultaneously,
and the approach to this procedure is inexpensive
and reliable. Furthermore, this approach facilitates
the use modern methods of image aquisition such as
processing and database integration. In addition the
technique translates well to computer image scoring
and tele-pathological consultancy.
One simple procedure
As in conventional formalin fixed or paraffin embedded
materials, a wide variety of techniques can be used
to analyze TMA. Researchers can perform histochemical
stains, immunohistological stains, in situ hybridization,
and tissue microsections. However, TMA allow multiple
samples to be analyzed all at once and on one slide.
Reagent concentrations, incubation times, temperatures,
washing conditions, etc., do not need to be optimized
individually. Furthermore, all the traditional methods
of antigen retrieval can be performed, such as steaming
or pressure cooking the slides.
Do many assays with only
a small amount of tissue
An entire cohort can be analyzed
in a single experiment, and only a very small amount
of reagent is necessary. Screening procedures which
were quite costly in the past can now be replaced
with TMA, allowing you even to do procedures which
would have been impracticable in the past.
The original block does not
need to be destroyed
Sometimes itxs necessary to the
return a conventional tissue block to the donor institution.
Yet, this doesn't present a difficulty when using
a TMA. The researcher need only core the block a few
times, enabling analysis of the sample. From here,
the original block can be returned to it's source.
Scarcity does not have to
be a limitation
In the hands
of an experienced and skilled technician, a standard
histological block can be cored as much as 100 times.
Therefore, up to 100 assays could be prepared from
a single archived block. Using a 0.6mm needle, itxs
possible to biopsy a sample 100 times or more. The
only limitation is the size of the original tissue
sample. Assuming the maximum optimization of a standard
tissue block, up to 10,000 tissue samples (100 cores
x 100 sections per block) could be taken from one
block. This translates to up to 10000 assays from
one tissue sample! I think youxll agree that TMAxs
are a powerful technique.
What procedure is used to process the donor
blocks?
For 18-24 hours, the tissues are fixed in 4% buffered
formalin, dehydrated with gradient ethanol and xylene
and then embedded in paraffin.
What storage conditions are recommended for
TMA, and can they be stored too long?
Regular buffered formalin will not prevent oxidation
after sectioning, and efficient production necessitates
the manufacture of large batches of tissue microarray
sections. This can result in antigenic loss due to
tissue oxidation. Coating the slides with an additional
thin layer of paraffin and storage at -80o C can prevent
this problem. When stored in this manner, the slides
can last up to 2 years.
Can the small cores really be representative
of the entire sample?
A suggested drawback of this technique has been that
the analyzed material is too small to represent the
entire sample. However, it has been demonstrated in
numerous studies that this is not the case. In fact,
some studies have shown quite clearly that between
two to four 0.6mm unique cores from the same sample
is all this is necessary to represent an entire section.
Using our TMA, this consistency is enhanced by RayBio®'s
1 mm, which is about 2.8 fold larger than that of
the 0.6 mm cores commonly used. Thus, our TMA present
an excellent representation of whole tissue sections
and have been demonstrated to be useful for histochemical,
immunohistochemical, and other in situ studies. Use
of multiple samples can eliminate variability by rapidly
increasing the data points available. Additionally,
you can multiply on the available data points available
by using custom TMA with duplicate, triplicate, and
quadruplicate cores.
Is it possible to analyze the protein expression
profile with TMA?
TMA are very effective for this purpose. There are
many options, you can either purchase TMA or request
immunohistochemistry service and analysis, and our
technicians can also do the immunohistochemical stain
for you. The protein expression profile will be examined
by our experienced pathologists. In four to six weeks,
you will receive an Expression Profile Analysis Sheet
complete with summary statement, stained tissue array
slides and microphotographs.
