FFPE (Formalin-Fixed Paraffin-Embedded) tissue specimens have played an integral role in research and therapeutic applications for decades. FFPE is the way biopsy specimens are preserved and prepared. The process ensures the specimens are suitable for examination, diagnostic/drug development, and experimental research. Once a tissue sample has been obtained, it is preserved. This process includes fixing it in formaldehyde, or formalin. It ensures the proteins and vital structures in the sample are preserved. After the tissue is preserved intact, it is embedded in a paraffin block. This process makes it easier to slice off the right size, so it fits on a microscopic slide for examining.
Methods of Tissue Collection
There are a variety of methods used for collecting tissue specimens. They can be obtained from both normal and diseased individual donors. Another method is to match a pair of samples from one person. This involves taking a sample of healthy tissue and one of diseased tissue from the same individual. Oncologists often use these types of samples for comparison. They can observe a primary tumor with a more distant metastatic tumor in one patient.
Tissue Sample Sources
Tissue is often excised for patients or donors. But it can also be obtained from other animals including mice or snakes. The block only has to measure a few centimeters, but the actual size may be determined by the tissue source and the nature of extraction. Immediately after excision, the tissue is immersed in a solution of 10% neutral-buggered formalin where it remains for 18 to 24 hours. This helps to harden the tissue so can endure the next steps.
FFPE Tissue Sample Preparation
The tissue must be dehydrated and cleared before being infiltrated with wax. This is often done using concentrates of ethanol. After it is dehydrated, it is embedded into IHC-grade wax or paraffin. Timing of fixation is vitally important to FFPE. If it is fixed too soon it can be useless for molecular biology studies. But they do need to be fixed long enough to preserve them. Mishandling samples can result in misleading deductions.
The method of FFPE tissue preparation depends on requirements as they are outlined by physicians or researchers who are requesting the tissues. They may have specifications about the size, purpose, or how it is cut. One example is muscle tissue which may be cut along the grain of the muscle fibers, or across the fibers. Certified medical pathologists are often involved in preparing samples to ensure the procedure is accurate, and to assess quality.
Storage of Prepared Tissue Samples
Once tissue samples have been completed, they are stored in a tissue bank, research center, or biorepository. Records are kept meticulously as to when tissue was collected and preserved. Other information such as the age, ethnicity, and gender of the donor as well as the origin, duration and the stage of diseased tissue are recorded. There are guidelines that must be followed such as obtaining signed consent forms and other legal documents. These can impact whether FFPE tissue can be used in clinical trials or in research. Once FFPE tissue slides are prepared properly, they are durable and can be stored at room temperature for years.
Applications of FFPE Tissue
FFPE tissue is often used in immunohistochemistry or IHC. This technique involves mounting the tissue sections on a slide, then they are covered with a solution that contains antibodies. The antibodies bind to specific structures or proteins. Then, stains are used to make the antibodies visible. This shows the types of structures or proteins are in the tissue sample and where they are located. Information like this is critically important in the medical field when doctors are looking for signs of diseases. IHC information is vital to many cancer research. Other applications include:
· Oncology – FFPE tissues are essential to the study of oncology or cancer.
· Hematology – FFPE tissue is vital in the study of blood and related disorders. Hematology has been key to discovering many cures for diseases caused by anomalies in the blood and its components.
· Immunology – Tissue samples from individuals who have an autoimmune disease help determine a cause and develop medication for treatment.
· Comparative – Tissue samples from healthy donors is beneficial for comparing with diseased tissue samples. This is imperative for research and development.
In Conclusion
It is certain that there is future work to be done using FFPE tissue samples. They provide a source of RNA, DNA, and proteins beneficial to medical research. The process must be protected to ensure high-quality standards are observed to ensure research and results are untainted.
Resources:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4077003/
https://pubmed.ncbi.nlm.nih.gov/18711211/
https://www.nature.com/articles/448959a
https://audubonbio.com/tissues/ffpe-tissue/
https://austinpublishinggroup.com/proteomics/fulltext/ap-v1-id1002.php
https://www.future-science.com/doi/10.2144/000114414
https://www.tandfonline.com/doi/full/10.1080/10520295.2018.1446101
