I currently work in a veterinary research core lab at a cancer research institute and we have used both the manual and automated process to create TMAs. In the past, we manually created TMAs by utilizing a punch biopsy tool. The recipient block would be created by using a special silicone TMA mold. The mold would be placed in the embedding unit to bring it up to temperature and then the liquid paraffin would be dispensed on top of the mold to fully submerge the core rods. Next, the cassette would be placed on top of the mold and the top of the cassette would be filled with more paraffin. The mold would cool to solidify the wax and then the mold is separated from the embedding cassette. Then a punch biopsy tool would be used to punch the areas of interest from donor blocks. A tissue punch plunger is then used to gently push the tissue core out of the punch biopsy and into one of the cores of the recipient block. Lastly, the recipient block is placed on a glass slide faced down and incubated in the oven to allow the cores to adhere to the recipient block. The temperature of the oven is dependent on the type of paraffin wax and the time to leave the block in the oven is dependent on temperature. The main pro to this manual method is cost. The silicone molds that can be reused hundreds of times and the biopsy punches are cheaper than a fully automated machine.
The main con is time and quality. Since a human is punching all the cores from the donor blocks and manually placing the cores into the recipient block, more time is needed and human error is possible. Sometimes if we were not gentle enough while inserting the recipient core into the donor block, the tissue core would break or the wax of the donor block would crack. There were also a few times during the oven incubation step that we forgot about the block in the oven and because the temperature was too high, it melted the block! (Always use a timer!!) Our lab also noticed the cores were not perfectly on the same plane (even after the oven incubation step) which resulted in microtomy issues of having full sections of some cores but not others.
TMAs that are made manually or from an automated tissue microarrayer are valuable tools. Researchers can perform immunohistochemistry or in situ hybridization to study the expression of specific proteins or genes across multiple samples on one slide. The data obtained from TMA studies can be used to identify potential biomarkers for diagnoses, prognosis, and treatment of diseases such as cancer, as well as to better understand the biology of diseases and how they develop. There can be challenges when creating TMAs but they can be incredibly useful.
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Written By: Sara Sheppard McCracken, BS, HTL(ASCP)QIHC
Sara would like to give credit to Arizona Ngyuen, HT (ASCP) for creating the TMAs that are shown in the images