College of American Pathologists
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  What are tissue arrays?




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April 2005
Feature Story

William Check, PhD

Though both "tissue array" and "microarray" include the word "array," they are radically different animals with radically different applications.

Tissue arrays are "a terrific way of confirming, validating, and extending findings from gene expression microarrays," says Matt van de Rijn, MD, PhD, associate professor of pathology at Stanford University School of Medicine. Tissue arrays may also find a place in routine clinical work.

A tissue array is basically a paraffin block containing tissue from hundreds of samples. "Let’s say 500 patients had a tumor removed from their lungs," Dr. van de Rijn says. "Those samples are languishing in paraffin blocks in the surgical pathology files. Now you have a new marker you want to look at." Rather than cut new sections from each of the 500 cases, which would be time-consuming and expensive, you make a tissue array by taking small cores from each existing paraffin block and arranging them on a new paraffin block. Next you cut a cross-section from that new block, which has each of these cores represented, and make a new slide. "You can take 100 or more sections from that array block, so you can do 100 stains and get 500 answers for each stain," Dr. van de Rijn says. "That makes it possible to do high-volume studies that would otherwise not be possible."

High-throughput tissue arrays were invented by a group at the Institute for Pathology of the University of Basel (Moch H, et al. Adv Anat Pathol. 2001;8:14-20). Dr. van de Rijn and colleagues have used them as a quality assurance tool for diagnostic immunohistochemistry (Hsu FD, et al. Mod Pathol. 2002;15:1374-1380) and to verify a subset of prognostic genes found on expression array profiling (Makretsov NA, et al. Clin Cancer Res. 2004;10:6143-6151).

William Check is a medical writer in Wilmette, Ill. The Roche/Affymetrix Amplichip will be covered more fully in the June issue in an article on clinical pharmacogenetics and laboratory medicine practice guidelines.