Tissue Microarray (TMA) Laboratory

Traditional screening for a new marker involves using multiple slides from many different patients. With this approach, the intensity and pattern of expression of the marker of interest must be evaluated in hundreds and sometimes thousands of slides. Over the past few years, a new methodology has become popular for performing these localization studies. This technique is called "tissue microarrays" (TMA) and is a mechanism that provides relatively high-throughput screening as well as significant reductions in time spent and tissue and reagent waste.

The TARPS TMA lab provides a state-of-the-art resource for tissue localization and target validation studies. In addition to routine processing and immunohistochemistry, this resource also provides quantitative imaging analysis and morphometry and digital imaging and photography facilities for use by researchers. A TMA consists of a paraffin block with an array of tissue cores from control and diseased tissues. Multiple cores from each patient specimen are included in a TMA block design to improve sampling accuracy and screening reliability. Incorporation of multiple cores helps eliminate errors related to tumor/disease sample heterogeneity. A minimum of two to six replicate tissue samples from the same morphologic area are inserted in the array to compensate for losses during processing, as well as to provide multiple samples for assay validation. Sections are cut from the TMA block for new assay development or reagent validation. Every fiftieth section is stained with H&E to confirm histology and provide a visual quality assurance mechanism.

There are three types of TMAs: (1) Multi-tumor Arrays are a TMA block with multiple samples from multiple patients, representing multiple tumor types (e.g., colon cancers, lung cancers, and prostate cancers), all in one block; (2) Progression Arrays contain multiple samples from a disease at various stages of disease progression (e.g., different grades and stages of prostate adenocarcinoma); and (3) Outcome Arrays may contain samples from similar histologic types of a disease, but from patients who have had different clinical outcomes (e.g., responders vs. non-responders to a particular therapy).

Tissue microarrays are ideal for efficient screening of putative biomarkers using a variety of techniques including immunohistochemistry, fluorescence in situ hybridization of nucleic acids (FISH), and RNA in situ hybridization. These techniques are used in tumor profiling, rapid screening of gene amplifications and translocations in cancer, for verification in tissue of differentially expressed genes that have been identified by cDNA arrays, and for screening potential prognostic and diagnostic markers.

TARPS provides research histologic support in the form of conventional tissue processing and histology as well as immunohistochemical localization support. The technical personnel have extensive experience in developing protocols for antibodies directed against novel markers. As part of this initiative, TARPS has dedicated considerable technical time to paraffin TMA development. TMAs allow novel marker assessment in a high throughput manner while very significantly conserving tissue and antibody usage. However, the generation of a TMA is very time and labor intensive. TARPS has developed TMAs for most common tumors. The TMAs are annotated with de-identified clinical and pathologic information and provided to the investigators. In addition, our software tools provide data storage and retrieval, thus allowing interesting data mining studies to evaluate utility of the markers under study through univariate and multi-variate analyses.