Tissue microarrays for high-throughput molecular pathology

Abstract

Modern research technologies, including DNA, protein, and antibody microarrays identify a steadily growing number of clues that are useful in molecular disease classification, drug development, and the prediction of response to treatment. Subsequent validation of the clinical importance of such candidate genes or proteins requires large-scale analysis of human tissues. To date, this analysis constitutes an important bottleneck in the process of discovery because tissue analysis by the conventional slide-by-slide strategy is slow and expensive. To overcome these limitations, tissue microarray (TMA) technology has been developed. TMA allows for the simultaneous analysis of up to 1,000 tissue samples in a single experiment, using all types of in-situ analyses including immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and RNA in situ hybridization (RNA-ISH). TMA technology has the potential to greatly facilitate the translation of basic research into clinical practice. Potential applications include the establishment of associations between molecular changes and clinical endpoints, testing of potential therapeutic targets using tissue samples from specific cancer patients, standardization of molecular detection of targets, and rapid translation of results from cell lines and animal models to human cancer. Because of its beneficial economic aspects and ability to differentiate ethnic differences in tumor biology, TMA applications may become particularly important in developing countries.

Figure 1

Tissue microarray (TMA) manufacturing. A) Donor block from which several 0.6 mm tissue cores have been removed. Note that the original tissue block remains fully interpretable. B) Recipient block with the completed TMA. C) Hematoxylin & eosin stained tissue section of the TMA. D) Magnification of a tissue spot.

Figure 2

Tissue microarray applications. Overview of TMA sections investigated by A) immunohistochemistry and B) RNA-ISH. C) Tissue spot showing focal expression (black granular staining) of BTG2 mRNA as investigated by RNA-ISH. The TMA section was coated with a photographic emulsion for detection of a radioactively labeled antisense-RNA probe. D) Tissue spot from a breast cancer array showing strong (3+) membranous staining of the HER2 protein by immunohistochemistry. E) Sector from the same tissue spot as in D) analyzed by FISH, using probes detecting HER2 gene amplification (clusters of red signals) and centromere 17 copy numbers (green signals).

Figure 3

Tissue microarrays from paraffin (A) and frozen tissues (B). TMAs from frozen tissues become more irregular and distorted than TMAs from formalin fixed material because the commercially available arrayers have not been designed for frozen array making. Therefore a larger space between samples is recommended (e.g., 1 mm).