“What is a Tissue Microarray?”
Tissue microarray is a recently-implemented pathological tool that provides high-throughput, multiplex analysis of different tissues and cells at the same time on a single histological slide. A single microarray actually consists of tissue samples that have been extracted from different paraffin donor blocks and re-introduced into a single paraffin block, at different array points.
This way, over a thousand tissue core samples can be analyzed simultaneously and cellular components such as DNA, RNA and proteins can be analyzed under similar standardized conditions, using the same diagnostic reagents on a single histological slide.
This technology facilitates the study of large sets of formalin-fixed, paraffin-embedded tissues both in prospective and retrospective sense.
What is so great about this technique is that it allows for maximal preservation and use of limited tissue resources. It provides a way to work around the rigid guidelines that back up the obtaining of human tissue. This way, scarce resources are used effectively.
Tissue microarray is commonly employed in immunohistochemistry, oncology analysis, and fluorescent in-situ hybridization.
One of the previous forms of tissue microarray was the multi-tumor “sausage” tissue block developed by Dr. Hector Battifora in 1986. The block consisted of a number of tissue samples thrown for the analysis of a single protein. Wan et al made an improvement to this technique in 1990: they used a 16-gauge needle to manually remove cores from tissues blocks and arranged them in a multi-tissue straw in a way they could identify the organ origin of the blocks. This was named accordingly as the “checkerboard tissue block”.
The final changes that made tissue microarray what it is today were made by J. Kononen and his collaborators in 1998.They developed a regular sample size by using a 4mm skin biopsy punch to remove a core from its donor block and recognize its position before transferring to the recipient block. This was how the more precise sampling technique of tissue microarray was born.
The sampling technique in tissue microarray usually involves a hollow needle used to remove tissue cores as small as 0.6 mm in diameter from different organ regions of
interest. These tissue cores are then inserted into a recipient paraffin block in a precisely spaced, array pattern. This recipient block can then be cut into 5μm sections using a microtome. These sections are then mounted independently on microscopic slides and are subjected to histological analysis. A single microarray block can be cut up into sections ranging from 100-500 in number, depending on the thickness of the block.
A variation in this procedure is seen in frozen tissue array in which up to 50 different sample cores, 2mm in diameter, of fresh frozen tissue are arrayed in a recipient block. The block is cut up in sections by a cryostat and then it follows the normal procedure of being mounted on a microscopic block and subjected to standard tissue analysis.
Tissue Microarray and Cancer
Tissue microarray has been recently implemented in the analysis of molecular markers in oncology research. It has been instrumental in tumor staging and in identifying new diagnostic and prognostic markers and targets in various human
cancers. It has a range of potential applications in basic research, prognostic oncology, and drug discovery. This technology has the potential to significantly accelerate cancer research.