From biopsies, surgical specimens or autopsies These are surplus specimens from the diagnostic process and can be preserved in various formats:

• Paraffin-embedded tissue: this is the standard diagnostic format as it is easy to process and can be stored at room temperature. The tissue structure remains intact, so it is useful for histochemical and immunohistochemical staining. Currently, by optimising commercial DNA and RNA extraction kits, it is also used for molecular biology techniques, although it is important to note the possibility of nucleic acid degradation.

• Frozen tissue (OCT or flash frozen): this format is used for research as it preserves biomolecules like DNA, RNA and proteins, allowing for genomic, transcriptomic and proteomic analyses. The tissue is submerged in Optimal Cutting Temperature (OCT) compound or liquid nitrogen (flash frozen).

• Fresh tissue: collection protocols vary and adapt to the needs of each project. With this format, there is no fixation of the tissue, allowing for cell cultures or isolations.