Source: emedicine.medscape.com Authors: Perminder S Parmar, MD et al. Introduction Since the draft sequence of the human genome was published in 2001 (Lander, 2001), the Cancer Genome Anatomy Project index of tumor genes has classified more than 40,000 genes directly or indirectly involved in one or more cancers (Strausberg, 2001; Strausberg, 2000). Conventional techniques of gene investigation in cancer rely on the identification of single genetic alterations associated with disease. This has proven to be both time consuming and cost ineffective. The introduction of complementary DNA (cDNA) microarray technology in 1995 (Schena, 1995) has helped to facilitate the identification and classification of DNA sequence information and the assignment of functions to these new genes by allowing investigators to analyze expression of thousands of genes simultaneously in a single experiment. Microarrays are a significant advance because they contain a very large number of genes and because of their small size. Therefore, microarrays are useful when one wants to survey a large number of genes quickly or when the study sample is small. Microarrays may be used to assay gene expression within a single sample or to compare gene expression in 2 different cell types or tissue samples, such as in healthy and diseased tissue. Because a microarray can be used to examine the expression of hundreds or thousands of genes at once, it promises to revolutionize the way gene expression is examined. Methods DNA microarrays are small solid supports onto which the sequences from thousands of different genes are attached at [...]