Gene Expression Detection Assay for Cancer Clinical Use

Narrandes, Shavira; Xu, Wayne

Principle Developed in 1998 by Kononen and associates, tissue microarrays (TMAs) require combining small tissue samples into "sausage blocks" to study the connection between the tissue samples on the slide with the clinical data. 67 By using in situ analyses, such as fluorescent in situ hybridization (FISH), RNA in situ hybridization (ISH), or immunohistochemistry techniques, TMAs can detect protein staining and cellular locations, offering its application in molecular diagnostic studies. However, the number of proteins to be detected is limited by the antibodies. 68 , 69 TMAs are expanded from gene expression serial analysis and cDNA microarrays so that they only require a single experiment to study the gene expression from many genes in a single tumor sample, allowing multiple patient samples representing various stages of a disease to be simultaneously investigated. 70 With the use of a TMA slide, probes for hybridization, and a signal detection instrument or scanner for data, followed by data analysis, TMAs offer the advantage of permitting a single set of tissues with associated clinical data to be used in various and unlimited studies. The steps generally required to prepare a TMA are as follows: preparation of a high-adhesive glass slide; acquisition of donor tissues; tissue core mapping and arrangement; sampling, sectioning, and transferring of the tissue donor cores; and tissue staining and molecular analysis. First, samples are taken from FFPE tissues. After mapping a tissue section stained with hematoxylin and eosin (H and E), a tissue arrayer removes cores from the donor block and places them in the recipient block.