Sabato 27 ottobre 2012 - Pacini Editore

COmuNiCaziONi ORali
7 Ellis I. Quality Assurance Guidelines for Breast Pathology Services
(second edition). Sheffield NHS Breast Cancer Screening Programme
July 2011. ISBN 978-1-84463-072-1 (NHSBSP publication n° 02).
Quality control by tissue microarray
in immunohistochemistry
S.A. Tripodi, B.J. Rocca, L. Hako, I. Monciatti, A. Carducci,
R.M. Ambrosio
Department of Human Pathology and Oncology, Pathological Anatomy
Section, University of Siena, Italy
Background. A growing number of immunohistochemical exams
is routinely required in histopathology, especially in the field
of hematopathology. In addition, there is a challenge to introduce
better quality assurance in immunohistochemistry. An external
positive control section is included in each immunohistochemical
analysis as a well-recognized and validated technique for standardizing
results. Unfortunately, this method is time-consuming
and expensive, significantly contributing to laboratory costs. On
the contrary, internal controls are warranted and inexpensive,
however their use is only feasible in selected diagnoses (i.e. basal
cells of normal prostatic glands as an internal control in high
molecular weight cytokeratin expression analyses for prostatic
cancer). Tissue microarray is a recent technique for the simultaneous
analysis of hundreds of tissues for protein, DNA and
RNA content. Recently, the tissue microarray technique has been
proposed as a tool for internal quality controls in immunohistochemistry.
This study presents a different strategy for introducing
an “internal” control in immunohistochemical analyses.
Materials and methods. A paraffin-embedded tonsil tissue
cylinder was sampled from a donor block using an automated
sampler and included as an ‘internal control’ together with a bone
marrow biopsy in a recipient block, avoiding the use of external
tonsil tissue control. To validate this technique, the authors compared
the quality of immunohistochemistry, the workload and
costs with routine external control in 50 consecutive bone marrow
biopsies over a 10-day period.
Results. In our method, only 8 seconds (7-minutes/50 biopsies)
were spent by technicians for picking-up a tissue core from the
donor tonsil block and adding it to the receiver block. In contrast,
in the routine method, technicians spent 3 minutes sectioning an
additional slide from the tonsil block with a total time of 180 minutes
for 60 external positive controls that were spared. Then, 200
additional minutes were needed to perform the immunoassay of
60 external positive controls. Thus, our method allows us to spare
a total of 373 minutes as well as all the reagents needed. In terms
of costs, since 15 Euros are needed to produce an additional slide
of tonsil tissue and 20 Euros are required for each immunohistochemical
test, 2100 Euros were spared during the 10-day test. The
volume of antibodies used for the analysis of each sample was
301
not increased and no other work was required. The workload of
the pathologist who had to interpret the slides was also decreased
because the control and the sample can be evaluated on the same
slide (at one glance). In fact there was always a clear separation
between the control tissue and the sample and the internal control
tissue core did not affect the immunostaining of the bone marrow
tissue. The quality of immunostain was good.
Conclusions. Commercial microarrayers, which can make thinner
tissue cores (from 0.6 to 2 mm) are increasingly common
in many university and research facilities, although inexpensive
disposable punch biopsies could also be employed. Thanks to our
method the consumption of “donor” tissue was low and dozens of
tissue cores were obtained from a single tonsillectomy specimen.
All the control tissues had a valid number of lymphoid follicles.
In future, the development of cell line tissue microarrays will
provide standard and widely available control samples for immunohistochemical
studies in many fields of pathology. In fact,
although the tonsil tissue displays a large number of antigens, in
specific cases it is essential to choose a more appropriate tissue
as positive control. Using this method, control and sample tissues
were processed at the same time, thus avoiding potential biases
during the different steps of the analysis. Most of all, the need for
an external positive control was avoided, reducing the costs and
laboratory workload. Furthermore, having both the control and
the sample on the same slide allowed immediate evaluation of the
immunostain, thus reducing the time required by the pathologist.
We successfully used this method of quality control in immunohistochemistry
from 2003 to the present for 2750 bone marrow
specimens, saving much money and improving quality.
In conclusion, the method of including tonsillar core tissue as an
“internal control” in bone marrow biopsies, improves quality control
in immunohistochemical analysis and achieves the important
aim of cutting laboratory costs. The method is applicable to many
fields other than haematopathology.
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