Introduction
Since the first appearance of tissue microarrays (TMA) more than 18 years ago, usage of TMAs by researchers from a wide range of disciplines has grown tremendously. By arraying different tumor types from multiple tissues on a single slide—oreven arraying with normal tissues, one can analyze a molecular target under highly controlled conditions. Because tissue samples are arrayed on the same slide, tissue morphology can be evaluated using H&E and stained with multiple antibodies specific to different molecular targets. Because of the format, TMAs are amenable to evaluation and analysis by way of either high-throughput automation or manual analysis using standard bright-field microscopy techniques.

Advantages
First described in published research by J. Kononen et al. (Nature Medicine Vol 4. No. 7, 1998 pp. 844-847), TMAs represent a significant advancement in molecular pathology over traditional methods, as they provide the ability to rapidly identify and characterize molecular targets in hundreds or thousands of tissue samples. TMAs are not constrained by technique or application, as slides can be probed using any assay protocol developed for whole tissue sections in a non-destructive manner. Thus, slides can be used for histology, immunochemistry, and FISH. Moreover, because of its miniaturization, an experiment using TMAs can be used to provide information on molecular and protein characteristics such as the incidence of molecular variations in tumor cells, cellular localization, or the detection and development of new prognostic or predictive indicators.

Given the high costs and extended time frames associated with bringing new drugs to market, these benefits make TMAs an ideal tool for primary evaluation of drug targets, as correlating gene and protein expression data in normal and diseased tissue samples can be obtained in a high-throughput manner. Additionally, the data can provide information crucial for rating and prioritizing molecular targets associated with particular clinical outcomes, thus helping to focus