Paraffin-embedded tissue is a fundamental tool in medicine and scientific research. This technique involves preserving biological samples within a block of paraffin wax, which stabilizes the tissue and maintains its structural integrity, allowing for detailed examination and long-term storage of tissue specimens.
What is Paraffin-Embedded Tissue and Why it is Used?
Paraffin-embedded tissue refers to biological samples, such as biopsies or surgical resections, that have been encased in paraffin wax. This method is widely used in histopathology to prepare tissues for microscopic examination. The primary purpose of embedding tissue in paraffin is to provide structural support, which allows for the cutting of extremely thin sections.
Embedding in paraffin stabilizes the tissue, preventing degradation and preserving cellular structures. This long-term preservation is important for diagnostic purposes, enabling pathologists to accurately identify diseases like cancer. This ensures tissue samples remain viable for future studies and retrospective analyses.
The Journey of a Tissue Sample
The transformation of a biological tissue sample into a paraffin-embedded block involves a series of steps. The initial step is fixation, where the tissue is immersed in a chemical solution, commonly formalin. This process prevents the tissue from decaying and helps to maintain the original cellular and tissue structures.
Following fixation, the tissue undergoes dehydration, a process where water is systematically removed from the sample. This is achieved by passing the tissue through increasing concentrations of alcohol. After dehydration, the tissue is subjected to clearing, where an agent like xylene is used to remove the alcohol. This step also makes the tissue transparent and prepares it to accept the paraffin wax.
Next, the cleared tissue is infiltrated with molten paraffin wax, which replaces the clearing agent. The tissue is then placed into a mold, where the molten wax solidifies around it, forming a stable block. This final paraffin block, known as a formalin-fixed paraffin-embedded (FFPE) block, provides the necessary rigidity for sectioning.
Unlocking Medical Insights from Tissue Blocks
Once a tissue sample is embedded in a paraffin block, it becomes a valuable resource for both disease diagnosis and medical research. For disease diagnosis, thin sections, typically ranging from 4 to 10 micrometers thick, are cut from the paraffin block using a specialized instrument. These delicate sections are then carefully placed onto glass slides.
The sections on the slides are then stained with various dyes to highlight cellular components, making them visible under a microscope. Pathologists examine these stained slides to identify abnormal cells, tissue architecture changes, and other indicators of disease, such as the presence and characteristics of cancerous tumors. This microscopic examination is a standard procedure in surgical pathology, allowing for precise diagnoses and guiding patient treatment plans.
Beyond immediate diagnosis, these paraffin blocks serve as an enduring archive for medical research. Stored indefinitely, they allow scientists to conduct retrospective studies, tracking disease progression over time or investigating the efficacy of past treatments. Researchers can extract various molecules from these archived tissues, including DNA, RNA, and proteins, to identify biomarkers, understand disease mechanisms, and develop new therapeutic strategies. This historical collection of preserved tissues is a unique and irreplaceable resource for advancing our understanding of human health and disease.