Surgical pathology is a specialized field of medicine focused on diagnosing disease through the gross and microscopic examination of tissues removed from living patients. Pathologists analyze these specimens to determine the presence, nature, and extent of a disease, most frequently focusing on whether a growth is benign or malignant. The findings from this analysis directly inform the treatment plan, guiding physicians toward the most appropriate next steps for patient care.
What Types of Samples Are Examined
The tissue specimens analyzed in surgical pathology vary widely in size and purpose. The smallest samples are typically biopsies, which are pieces of tissue removed primarily to establish a diagnosis. Core needle biopsies, for instance, use a large-bore needle to extract a small cylinder of tissue while preserving the cellular architecture, allowing for initial characterization of a lesion.
Incisional biopsies remove only a portion of a suspicious mass, while an excisional biopsy removes the entire lesion, acting as both a diagnostic and potentially therapeutic procedure. Contrastingly, surgical resections involve the removal of entire organs or large tumor masses. The pathological analysis of these larger specimens is performed to confirm the diagnosis, stage the disease, and ensure complete removal.
A particularly time-sensitive sample is the frozen section, which is an intraoperative consultation performed while the patient remains under anesthesia. The pathologist rapidly freezes the fresh tissue, slices it, and stains it to provide a preliminary diagnosis, often in under 20 minutes. This rapid feedback allows the surgeon to make immediate decisions, such as whether to remove more tissue, assess a surgical margin, or determine if a lymph node contains cancer cells.
The Journey of the Tissue Sample
Once a specimen is removed from the patient, it begins a meticulous, multi-step process to transform it from raw tissue into a stained slide suitable for microscopic review. The initial step is Gross Examination, where a pathologist or pathologist’s assistant visually inspects the specimen, measuring its dimensions, weight, and describing its color and texture. The grossing step is where a tumor’s size and relationship to its surgical margins are first documented, and it is here that small, representative pieces of tissue are selected and placed into small plastic cassettes.
Following grossing, the tissue pieces must be preserved through fixation, typically by immersion in a 10% neutral buffered formalin solution. This chemical process stabilizes the tissue’s proteins, preventing degradation and decay that would compromise cellular detail. This preservation usually takes between 6 and 48 hours, depending on the size of the tissue fragment.
The next major phase is tissue processing, which prepares the fixed tissue for slicing by embedding it in a solid support medium. Because paraffin wax is used for support and is immiscible with water, the water in the tissue must first be removed through dehydration using increasing concentrations of alcohol. After the alcohol is removed, a clearing agent like xylene is used to make the tissue receptive to the final embedding medium.
The tissue is then placed into a mold and infiltrated with molten paraffin wax, which solidifies to form a durable tissue block. This solid block is mounted in an instrument called a microtome, which is used to cut the tissue into ultra-thin sections, usually only 3 to 5 micrometers thick. These fragile sections are floated onto a warm water bath and then carefully mounted onto glass slides.
The mounted sections are then subjected to staining to make the cellular structures visible under the microscope. The standard procedure is the Hematoxylin and Eosin (H&E) stain, which uses two dyes to provide contrast. Hematoxylin, which is a basic dye, stains the acidic components of the cell, such as the DNA in the nucleus, a purplish-blue color. Eosin, an acidic dye, stains the basic components, primarily the proteins in the cell’s cytoplasm and the extracellular matrix, shades of pink. Finally, the pathologist examines this colored slide to render the definitive diagnosis.
How the Surgical Pathology Report Guides Treatment
The resulting surgical pathology report serves as the foundation for all subsequent patient management decisions. Beyond confirming the diagnosis, the report provides several pieces of data that dictate whether further surgery or different therapy is required. One of the most important factors is the margins status, which refers to the edges of the surgically removed tissue.
A negative or “clear” margin means the pathologist found no cancer cells at the very edge of the resected tissue, suggesting the entire tumor was removed. Conversely, a positive or “involved” margin indicates that cancer cells extend to the edge, signaling that some disease may remain in the patient and often necessitating a second surgery, known as a re-excision. Pathologists use special ink to mark these margins while the specimen is still intact, ensuring precise communication with the surgeon about the exact location of any remaining disease.
The report also includes tumor grading and staging, which are measures of the tumor’s aggressiveness and extent of spread. Grading is a microscopic assessment where tumors are classified based on how closely the cancer cells resemble normal cells, typically on a scale like G1 (well-differentiated and less aggressive) to G4 (undifferentiated and highly aggressive). Staging, often using the TNM system (Tumor size, lymph Node involvement, Metastasis), is a far-reaching measure of the disease’s physical extent, determining prognosis and the need for systemic therapy.
In the era of personalized medicine, the report often includes results from ancillary testing, such as immunohistochemistry (IHC) and molecular diagnostics. IHC uses antibodies to identify specific proteins on the cancer cells, such as hormone receptors or the HER2 protein in breast cancer. Identifying these molecular targets allows oncologists to select targeted therapies, transforming the pathologist’s role into a direct guide for precision treatment.