The technology of tissue microarrays (TMAs) was developed against the background of decoding the human genome and the widespread application of high-density cDNA microarrays. TMAs facilitate comprehensive molecular profiling of cancer specimens with minimal tissue requirements. A TMA is a paraffin block composed of multiple tissue specimens. TMA sections provide targets for parallel in situ detection of DNA, RNA, and protein targets, allowing the rapid analysis of hundreds of molecular markers in the same set of specimens. Multiple specimens can be simultaneously investigated with different in situ techniques under identical laboratory conditions.