Dr. NIMRAH AMJAD

 Tissue microarray (TMA) is a method used to
evaluate numerous samples of tissue in a
short time.
 First introduced { Battifora (1986) }
 Multiple tissue samples arranged in a single
paraffin block

 Microarray contains many small
representative tissue samples from hundreds
of different cases assembled on a single
histologic slide
 Allows high throughput analysis of multiple
specimens at same time

 In the tissue microarray technique, a hollow
needle is used to remove tissue cores as
small as 0.6 mm in diameter from regions of
interest in paraffin-embedded tissues such as
clinical biopsies or tumor samples. These
tissue cores are then inserted in a recipient
paraffin block in a precisely spaced, array
pattern.

 Tissue microarrays are paraffin blocks
produced by extracting cylindrical tissue
cores from different paraffin donor blocks
and re-embedding these into a single
recipient (microarray) block at defined array
coordinates.

 Experimental applications
 Clinical applications

 Array comparative genomic hybridization
(aCGH)
 Genotyping
 Sequencing
 Genome tiling
 Gene expression

 Gene expression profiling as an ancillary
diagnostic tool for the pathologist
 Predicting disease behavior
 Predicting survival
 Predicting therapeutic response
 Nontumor pathology

 Genotyping
 Genome copy number
 Methylation
 DNA sequencing

 Amplification of a scarce resource
 Simultaneous analysis of very large numbers of
specimens
 Experimental uniformity
 Decreased assay volume, time and cost effective
 Does not destroy original block for diagnosis and
conserves valuable tissue

 Used as quality control in H&E and IHC
 Used for wide range of staining procedures,
IHC, ISH, FISH, Special stains and H&E
 Enable study and evaluation of many
diseases(diagnostic tool)
 In Clinical pathology as quality control for
new antibodies

 Tissue heterogenity
 One of the most common criticisms of tissue
microarray is that the small cores sampled
may not be representative of the whole
tumor, particularly in heterogenous cancers
such as prostate adenocarcinoma and
Hodgkin lymphoma

 Determine which blocks will be arrayed
 Mark the area of interest either on the slide or
block
 Both should be marked in same area
 At least 1mm thick
 If marked area< 1mm thick , two cores are
stacked on top of each other

 Color indicators:
RED------------CANCER
GREEN----------NORMAL
BLACK----------PRE-INVASIVE

 Four sizes:
 0.6 , 1.0 , 1.5 , and 2.0mm
General use
Ideal spacing-----------0.1mm

 Blank paraffin wax block
 There should be no holes in the block caused
by air bubbles
 1.0mm needle preferred: gives a desireable
core and leaves little distortion in donor block
 Ensure the alignment of punches

 Smoothing and Sectioning
 Microtomy
 Troubleshooting and tips:
 Core doesn’t come out easily, punch tip is
bent, change it
 Tissue core pushed too deep

 Insufficient spacing of core
 Thinning of cores in the block, uneven cores
 Loss of tissue on water bath
 Refacing block
 Refacing angle