Can customized tissue microarrays mix tumors from different organs and normal tissues on a single slide?

The key is to confirm whether the other party has experience handling mixed organs and cryopreserved tissues. You can request a few test spots first to see whether liver, stomach, and breast tissue sections remain intact after being placed in the same recipient wax block and whether the edges detach. The quality of cryopreserved tissues varies; before library construction, it is best to perform HE morphological assessment or RNA quality spot checks to avoid discovering after all the money has been spent that the spots have no diagnostic value. The contract should specify that if cryopreserved samples cannot form spots or fail morphological qualification, samples can be replaced or the number of spots reduced. For mixed chips, it is also necessary to confirm how the final array map, spot coordinates, and pathology numbers are matched.

Tumors and normal tissues from different organs can be placed on the same chip, but they should not be randomly distributed. It is best to divide them by cancer type, with each of liver cancer, gastric cancer, and breast cancer having its own normal controls and blank positions. This avoids mutual interference of antigen retrieval conditions among different tissues and facilitates archiving after staining. Tissue blocks from different organs vary greatly in hardness, which may result in inconsistent depths during spotting, and fragile liver and breast tissues are prone to fragmentation. Before designing, have the supplier evaluate the thickness of each wax block. If necessary, concentrate the same cancer type in one region and add orientation markers; otherwise, it is easy to misalign the spots after scanning.

Frozen tissue cannot be directly used for microarray punching; it must first be fixed, dehydrated, and embedded into donor paraffin blocks. Because tissue microarrays involve taking cores from donor paraffin blocks and then arranging them into recipient paraffin blocks, direct sampling from frozen tissue cannot ensure morphology, and sections will fragment or fail to form intact sections, as well as contaminate the needle. It is recommended to first process frozen samples into paraffin blocks according to standard procedures and perform HE evaluation before proceeding to arraying. If the frozen tissue has been embedded in OCT, do not directly punch from the OCT block; it must also be re-embedded. This step will add at least 2–4 days, depending on tissue size and the dehydration protocol.

The cycle should account for the time required to re-embed the cryopreserved samples. For the paraffin block portion, if the quality is good, 80 spots with 2 spots per case, routine production generally takes several working days, but fixation and dehydration of cryopreserved tissue will add several extra days, so it is recommended to allow more than 10 working days for the entire project. Finished tissue microarray paraffin blocks are recommended to be stored at 4°C to avoid repeated freeze-thaw cycles; white slides are best used short-term at room temperature or 4°C after sectioning, and for long-term storage, low-temperature drying is recommended to avoid moisture and oxidation. If the cryopreserved tissue will subsequently be used for RNA or protein analysis, it is best to save a separate portion of unembedded cryopreserved sample rather than processing all of it.