Optimization of the capture of â€œdifficult targetsâ€ in tissue microarrays

Optimization of the capture of “difficult targets” in tissue microarrays Chris Moskaluk University of Virginia

The “perfect” tissue target approximates a cylinder with sides parallel to the direction of the TMA sampling needle, and that extends to the full thickness of the paraffin block.

Some target tissues are thin, requiring double sampling with the TMA needles, with subsequent stacking of the tissue cores in the TMA block.

“Double stacked” TMA cores

Some target tissues veer off at acute angles from the surface of the donor paraffin block. The course of the target tissue cannot be predicted from examination of the guide H&E histologic section.

Target tissue is often a complex 3 dimensional structure within the donor paraffin block. Larger cores or multiple sampling may be required to effect capture of target tissue in serial sections of a TMA block.

Optimization study • Hypothesis: larger core sizes will capture more tissue • Core sizes: 0.6, 1, 1.5, 2 mm • Area increases as a square of the radius • What number of what size cores are needed to capture “difficult” targets for at least 100 histologic sections?

TMA spot sizes 20 X original magnification

Optimization study • Target tissues • Brunner glands of duodenum • Breast lobules and ducts • Bile ducts in liver portal tracts • Pancreatic islets • 5 different donor blocks per target tissue • 2 duplicate microarrays • 0.6 mm cores: 10 x 2 = 20 • 1 mm cores: 10 x 2 = 20 • 1.5 mm cores: 4 x 2 = 8 • 2 mm cores: 4 x 2 = 8

TMA block with 0.6, 1, 1.5 and 2 mm tissue cores

% capture (per core) Tissue spot diameter Histologic level

Conclusions • The number and the size of TMA cores needed to efficiently capture target tissue will depend on the specific tissue target • For the most difficult targets, at least two “large cores” (1.5 or 2 mm) may be required

Optimization of the capture of â€œdifficult targetsâ€ in tissue microarrays