Formalin-Fixed Paraffin-Embedded, or FFPE, describes a widely used method for preserving biological tissue samples. This technique allows for the long-term storage and subsequent examination of tissues, acting as a foundational approach in both modern medical practice and scientific investigation. Its widespread adoption stems from its ability to maintain tissue architecture and cellular components for extended periods, enabling detailed analysis. This preservation method plays an important role in understanding diseases and advancing biological knowledge.
The FFPE Preservation Process
Fixation begins the FFPE preservation process, where the tissue is immersed in a chemical solution, most commonly a 10% neutral buffered formalin. Formalin cross-links proteins within cells and tissues, effectively locking all cellular components in place. This halts decomposition and prevents degradation of cellular structures, preserving tissue integrity for future study.
Following fixation, the tissue undergoes dehydration, where water is gradually removed from the sample. This is achieved by passing the tissue through increasing concentrations of alcohol, typically ethanol. Once dehydrated, a clearing agent, often xylene, removes the alcohol and prepares the tissue for the next phase.
The cleared tissue is then infiltrated with molten paraffin wax, where the wax permeates the tissue, replacing the clearing agent. This step provides structural support to the tissue. Finally, the wax-infiltrated tissue is placed into a mold filled with molten paraffin, cooled to solidify, forming a stable, solid block. This block protects the tissue indefinitely, ready for precise slicing.
Application in Medical Diagnosis
FFPE tissue blocks are important in medical diagnosis, particularly for identifying diseases like cancer. When a patient undergoes a biopsy, a small tissue sample is taken and immediately processed into an FFPE block. This block allows pathologists to obtain thin slices, typically 3 to 5 micrometers thick, using a microtome.
These sections are then mounted on glass slides and stained to highlight cellular structures. Pathologists examine these stained sections under a microscope, looking for abnormal cell shapes, tissue organization, and indicators of disease. This examination enables accurate diagnoses, guiding treatment decisions. The FFPE block also serves as a permanent record of the patient’s tissue, stored for decades and re-examined if questions arise or new diagnostic techniques become available.
Significance in Scientific Research
Beyond individual patient diagnosis, FFPE tissues hold significance for scientific research. Many institutions maintain vast collections of FFPE blocks, often called biobanks or tissue archives, containing samples from thousands of patients spanning decades. These libraries provide a resource for researchers studying diseases.
Scientists access these collections to investigate disease progression, identify biomarkers, or explore the effects of conditions on human tissue. Researchers might use these archived samples to compare tissue from patients with a specific disease to healthy controls, searching for patterns or molecular changes. This allows for retrospective studies that can uncover new insights into disease mechanisms and therapeutic targets without the need for immediate clinical trials.
Methods for Analyzing FFPE Tissue
Once an FFPE block is prepared, several laboratory techniques can be applied to its thin sections. Histology is the fundamental method, involving the microscopic study of tissue structures. The most common histological stain is Hematoxylin and Eosin (H&E), which colors cell nuclei blue and the cytoplasm and extracellular matrix pink, providing an overview of tissue morphology.
Immunohistochemistry (IHC) is an advanced staining technique that uses antibodies to detect specific proteins. These antibodies bind to their target proteins, and a chemical reaction makes these proteins visible, often as a distinct color or fluorescent signal. IHC is used to identify specific types of cancer cells or to determine the presence of protein markers that might indicate how a tumor will respond to therapies.
Molecular analysis, including DNA and RNA extraction, can also be performed on FFPE tissue. While formalin fixation can sometimes cause minor damage or fragmentation to nucleic acids, advancements in molecular biology techniques make it possible to reliably extract and analyze genetic information from these samples. This allows researchers to study gene mutations, gene expression patterns, or viral sequences within the preserved tissue, providing insights into disease mechanisms at the molecular level.