What are Tissue Microarrays?

Tissue microarrays, also referred to as TMAs, are selections of tissue cores prepared in a paraffin block and arranged in a precise array fashion. Histological sections of the array can be cut from the paraffin block, resulting in thin slices of the paraffin-prepared tissue array that can be placed on a regular microscope slide. Tissue microarrays are used to conduct a wide variety of tests on numerous tissue samples contained on a single microscope slide, allowing for great speed and precision in experimentation. Scientists, for example, often use tissue microarrays to determine gene expression in normal and in pathological tissues in order to use genetics to diagnose various diseases.

Many different labs, mostly in biological and health research, use tissue microarrays to improve the efficiency and precision with which they can run various experiments on tissue samples. Immunohistochemistry, for example, is a process in which fluorescent agents are attached to antibodies which are exposed to tissue samples on a microarray. The antibodies bind to specific antigens on the tissue samples and researchers can identify this binding because of the fluorescent agents. Certain specific antibodies bind to specific antigens, so binding levels can provide a great deal of information about the antigens contained in a given tissue sample. Different antigens may be present on normal or pathological cells; understanding the difference can allow for accurate disease diagnosis and may even provide information that can be used to find cures for various illnesses.

A similar technique that is commonly applied to tissue microarrays is called Fluorescent in situ hybridization, or FISH. In FISH, fluorescent probes bind to particular parts of chromosomes and can be used to find information about an individual's genetic makeup. This method can, for instance, be used to identify genetic markers for various diseases. Both FISH and immunohistochemistry methods are commonly used to diagnose and to identify treatments for cancer.

Tissue samples can be difficult to obtain in significant quantities, and tissue microarrays tend to take quite some time to prepare, so researchers must ensure their samples remain intact and that the array is prepared correctly. Tissue, for example, must be quickly processed in paraffin to prevent decay. Some researchers choose to purchase pre-made tissue microarrays instead of producing their own to avoid errors while preparing their own tissue microarrays. Another consideration is the number of samples to be placed on a single slide. Several hundred tissue cores can be placed on a single slide, but it may be difficult to keep track of and to precisely experiment on that many small samples.