What is Formalin Fixed Paraffin Embedded (FFPE)?
Formalin Fixed Paraffin Embedded (FFPE) is a method widely used in
histology for the preservation and preparation of tissue samples. This technique involves fixing the tissue in
formalin to preserve its structure and then embedding it in paraffin wax to create a solid block that can be easily sectioned for microscopic examination.
Why is Formalin Used for Fixation?
Formalin, a solution of
formaldehyde in water, is used for fixation because it effectively preserves tissue morphology and cellular details. Formalin cross-links proteins, which helps to maintain the integrity of cell structures and prevents enzymatic degradation and bacterial growth.
Fixation: The tissue sample is immersed in formalin for a specific period, which can range from a few hours to several days, depending on the size and type of tissue.
Dehydration: The fixed tissue is then dehydrated through a series of graded alcohol baths to remove water.
Clearing: The dehydrated tissue is treated with a clearing agent, such as
xylene, to remove alcohol and make the tissue transparent.
Embedding: The cleared tissue is infiltrated with molten paraffin wax and then allowed to solidify, forming a paraffin block.
Sectioning: The paraffin block is cut into thin sections using a
microtome, and the sections are placed on glass slides for staining and microscopic analysis.
Long-term preservation: FFPE blocks can be stored for many years, making them suitable for retrospective studies.
Structural preservation: The fixation process maintains cellular architecture and tissue morphology, allowing for detailed histological analysis.
Compatibility with staining: FFPE sections can be stained with a wide range of
histological stains to highlight different tissue components and pathologies.
Molecular studies: FFPE samples can be used for
molecular techniques such as immunohistochemistry and DNA/RNA extraction, although with some limitations.
Degradation of nucleic acids: The fixation process can cause fragmentation and chemical modification of DNA and RNA, which may affect molecular analyses.
Antigen retrieval: Formalin fixation can mask
antigenic sites, necessitating antigen retrieval steps before immunohistochemical staining.
Artifacts: The processing steps can introduce artifacts, such as shrinkage, which may complicate the interpretation of histological findings.
Applications of FFPE in Histology
FFPE is extensively used in various fields of histology and pathology: Diagnostic pathology: FFPE sections are essential for diagnosing diseases, including cancers, inflammatory conditions, and infectious diseases.
Research: FFPE samples are used in research studies to understand disease mechanisms, identify biomarkers, and develop new therapies.
Tumor profiling: FFPE tissues are analyzed for
tumor biomarkers to guide personalized treatment strategies.
Biobanking: FFPE blocks are stored in biobanks for future research and clinical applications.
Conclusion
Formalin Fixed Paraffin Embedded (FFPE) remains a cornerstone in the field of histology due to its ability to preserve tissue morphology and facilitate a wide range of diagnostic and research applications. Despite some limitations, ongoing advancements in molecular techniques and antigen retrieval methods continue to enhance the utility of FFPE samples in modern histopathology.
