The removal of a tumor during surgery is the initial step in a complex process of diagnosis and treatment planning. The specimen transitions from the operating room to the pathology laboratory, where its analysis dictates the patient’s official diagnosis, determines subsequent therapy, and affects the prognosis. Strict protocols govern this process to ensure the integrity of the tissue for accurate scientific analysis.
From Operating Room to Laboratory
Immediate handling of the surgical specimen is paramount to preserving its cellular structure for later microscopic examination. To halt tissue decay and maintain the integrity of proteins and DNA, the specimen must be promptly stabilized through fixation. This period before stabilization is known as “cold ischemic time.” Fixation is typically achieved by immersing the tissue in 10% neutral buffered formalin.
The specimen must also be meticulously labeled and documented to maintain the chain of custody, ensuring the tissue is correctly paired with the patient’s medical chart. The container is then sealed and transported immediately to the pathology department.
The Diagnostic Journey: Gross and Histological Examination
Upon arrival, the specimen is logged into the system, and the gross examination begins. A pathologist or trained assistant visually inspects the mass, measuring its dimensions, weight, color, and texture. For larger specimens, the tumor may be sliced to allow the fixative to fully penetrate the center.
A primary step is the assessment of surgical margins, checking whether the tumor extends to the edges of the removed tissue. If cancer cells are found at the margin, it suggests the entire tumor may not have been removed, potentially requiring further treatment. Representative sections of the tumor and margins are then selected and placed into labeled plastic containers called cassettes, which proceed to the tissue processor.
The tissue processor takes the fixed samples through a series of chemical steps designed to replace the water in the cells with a solid embedding medium. This process begins with dehydration, where the tissue is immersed in increasing concentrations of alcohol to remove all water. Following this, the tissue is infiltrated with and then embedded in molten paraffin wax, which solidifies into a rectangular “tissue block.” This hard wax block provides the necessary support for extremely thin slicing.
A specialized instrument called a microtome cuts sections of the tissue block, typically only 4 to 5 micrometers thick, which are floated onto glass slides. The final step is staining the slides to make cellular structures visible under a microscope. The standard method is the Hematoxylin and Eosin (H&E) stain. This staining allows the pathologist to examine the morphology, determine if the tumor is benign or malignant, and assign a preliminary grade based on cellular appearance.
Molecular Analysis and Precision Classification
For many malignant tumors, the initial morphological assessment is insufficient to guide modern treatment, necessitating specialized molecular testing. This analysis uses unstained tissue sections cut from the original paraffin block. One common technique is Immunohistochemistry (IHC), which uses targeted antibodies to detect specific proteins or receptors on the cancer cells.
IHC determines the expression status of predictive markers, such as the estrogen receptor (ER), progesterone receptor (PR), or HER2 protein in breast cancers. The presence or absence of these proteins informs the use of targeted therapies. Other IHC markers help categorize the tumor subtype and predict responsiveness to treatments like immunotherapy.
Beyond protein expression, modern oncology often requires deep genetic and molecular analysis to pinpoint specific mutations. Techniques like Next-Generation Sequencing (NGS) and Polymerase Chain Reaction (PCR) are used to analyze the tumor’s DNA and RNA. These tests can identify actionable mutations in genes like BRAF or KRAS that might predict a response to certain chemotherapy agents or a lack of response to others.
The comprehensive findings from the morphological and molecular analyses contribute to the formal clinical staging of the cancer, often using the TNM (Tumor, Node, Metastasis) classification system. The final pathology report integrates the tumor size, cell grade, margin status, and molecular profile to provide the treating physician with the complete picture necessary to determine prognosis and plan precise treatment.
Archiving and Final Disposition of the Specimen
After the diagnostic process is complete and the final pathology report is issued, the physical materials are prepared for long-term storage. The paraffin blocks and corresponding glass slides are considered irreplaceable archives of the patient’s disease. These materials are stored in highly organized pathology archives, often for 10 to 25 years, depending on local regulations.
Archiving is essential because the blocks and slides may be needed years later for a second opinion, new molecular testing, or research. Patients retain the right to request access to their archived materials for consultation. The bulk of the tumor tissue that was fixed but not sampled for the paraffin blocks is treated as biohazardous waste. This residual tissue is disposed of according to strict health and safety regulations, typically through incineration.