Introduction to Tissue Blocks
Formalin Fixed Paraffin Embedded (FFPE) tissue specimens are used mostly by the medical community and researchers to preserve biopsy samples in formaldehyde and is then embedded into a paraffin wax block. This process preserves the proteins and structures of the tissue. After it is preserved into blocks, thin slices of the FFPE block can be made and is then mounted on a microscope slide to enable examination. The preparation and storage of FFPE tissue is not confined to human tissue but includes specimens from mice, rats, primates, and any other living creature. Specific requirements of buffer concentration and process are required. Tissue blocks and slides that are prepared properly can be stored for a long duration, archived, and used retrospectively for research and clinical studies.
Uses of FFPE Tissue Blocks
The immunohistochemistry technique is often used in FFPE tissue blocks. The slides are mounted on a slide and bathed in solutions that contain antibodies that specifically bind particular proteins and structures. To visualize the antibodies, stains are used to show if proteins or structures are present in the sample. Clinically and research wise, this can be crucial as it can help in the identification of signs of cancer, Alzheimer’s disease, and more. The information gathered is vital in clinical studies that are being conducted today. The only disadvantage to this procedure is that the formaldehyde fixation process may denature certain proteins and hence, may be invisible to the antibodies that are detected to detect them. FFPE tissue blocks can also be used to recover DNA, RNA, and proteins via newly developed techniques. This is a huge opportunity as it opens up the opportunity of having a vast source of preserved and annotated material that can be utilized in molecular biology and biochemistry studies.
Therapeutic areas where FFPE Specimens Can Be Used
Quality FFPE specimens are critical in clinical studies and research. Since FFPE specimens are a relatively inexpensive and easy way to store, more future work can and will be done using FFPE blocks if DNA, RNA, and proteins are needed.
- Oncology – Preserved tumor tissues have characteristic morphologies that can be used in clinical or diagnostic purposes. Immunohistochemistry can be used to detect specific proteins. The identification of these antibodies can be helpful in diagnostics and determine if treatment could be successful.
- Hematology – Preserved bone marrow has shown that it is involved in toxicology, tissue regeneration, genetics and thus, helped in the discovery of cures to diseases and anomalies of the blood.
- Immunology – Preserved tissue from an individual with autoimmune disease has helped to determine response of the immune system in a diseased state, cause, and possible medication that may aid in the condition of the defect.
- Normal – Preserved tissue from normal individuals devoid of diseases or any conditions can be used for comparative studies in all studies.
FFPE blocks are also commonly used in Tissue Microarrays (TMAs). TMAs are constructed by transferring cores from FFPE blocks to spatially fixed locations in a recipient block. From the FFPE block, a small 0.6-3mm punch is taken and is then seated into the recipient block. Cores or punches can be done using a manual or automatic tissue array. Once constructed, it can then be sectioned and mounted on a microscopic slide. TMAs is a technique that can be highly effective when there is shortage of tissue specimens. Some of the advantages include:
- Efficient – In conventional slides, only one case can be studied per slide. Using TMA, every slide can be used in 50-500+ cases. Besides that, compared to conventional slides where 150 sections of one case yields 150 assays, in TMAs, 150 sections with 500 cases can yield up to 75,000 assays.
- Time – In a single experiment alone, the entire cohort of study can be done if FFPE blocks are utilized. Results are also rapid in large cohorts.
- Cost – The TMA technique requires very little (less than 1ml) total reagent volume for the whole cohort.
- Simple – TMA is not subject to differential antigen retrieval.
- Staining – Just like Conventional FFPE, TMAs are also agreeable to variable methods of staining such as chromogenic or fluorescent visualization, in situ hybridization, tissue microdissection, and more.
- Tissue retention – Since FFPE can be used in TAs, FFPE blocks can be cored several times without destroying the block.
- Longevity – Studies have found and demonstrated that FFPE blocks for more than 60 years, making it valid in the study of archival tissues.
FFPE is a great commodity to the research and medical field as it is an inexpensive and easy way to store and archive tissue specimens. It also preserves the integrity of the specimen for a long time and can therefore be used retrospectively in many studies which reduces the time needed to track down specific tissues that fit the criteria of the study. It is like a “bank” that can be accessed by professionals to conduct research on in order to ensure progress of the medical and scientific industry.