Cancer pathology is the medical field that diagnoses disease by examining tissue and cells under a microscope, serving as the definitive method for confirming cancer. A pathologist analyzes tissue samples to identify a disease’s characteristics, providing foundational information for treatment decisions. These findings are compiled into a detailed report confirming the cancer’s presence and type.
From Biopsy to Slide
The diagnostic journey begins with a biopsy, where a small piece of tissue is removed for testing. Common types include needle biopsies, which extract a core of tissue, and excisional biopsies, which remove an entire lump. The sample is placed in a formalin solution, a chemical fixative that preserves the tissue and prevents decay, maintaining its cellular structure for examination.
After fixation, the tissue is processed in a laboratory. It is dehydrated and embedded in a paraffin wax block to create a stable sample. This block is mounted on a microtome, an instrument that slices it into extremely thin sections. These translucent ribbons of tissue are then placed on glass microscope slides.
Before examination, the tissue must be stained to make its components visible. The standard method is Hematoxylin and Eosin (H&E) staining. Hematoxylin stains cell nuclei purplish-blue, while eosin stains the cytoplasm and connective tissue in shades of pink. This contrast reveals the tissue’s architecture and the morphology of individual cells.
Deciphering the Pathology Report
The pathology report is a medical document summarizing the pathologist’s findings and providing a definitive diagnosis. The first determination is whether the tissue is benign (non-cancerous) or malignant (cancerous). Malignant cells can invade nearby structures and metastasize, while benign tumors do not.
Tumor Grade
Tumor grade describes how much cancer cells resemble healthy cells. Well-differentiated cancers have cells that look more like normal cells and tend to grow slowly. In contrast, poorly-differentiated or high-grade cancers have highly abnormal-looking cells, indicating a faster-growing and more aggressive cancer.
Surgical Margins
For cancers removed surgically, the report describes the surgical margins. A “negative” or “clean” margin means no cancer cells were seen at the outer edge of the removed tissue, suggesting a complete removal. A “positive” margin indicates cancer cells were found at the edge, raising the possibility that some cancer was left behind.
Lymph Node Status
The report also includes the lymph node status. The pathologist examines lymph nodes removed from near the tumor to see if cancer has spread into them. The presence of cancer in lymph nodes is a sign that the disease has begun to move beyond its original site.
Molecular and Genetic Analysis
Modern pathology often extends beyond visual inspection to include molecular and genetic testing of the cancer cells. This analysis identifies specific biomarkers—proteins or gene mutations—that can drive a cancer’s growth. This information is used to create personalized treatment plans.
One common technique is Immunohistochemistry (IHC), which uses antibodies to detect specific proteins in a tissue sample. For example, in breast cancer, IHC tests determine if cells have receptors for estrogen (ER) and progesterone (PR), or if they overproduce a protein called HER2. These results guide the use of hormone therapies or drugs that target the HER2 protein.
In addition to protein analysis, pathologists test for specific genetic mutations within the cancer cells. Certain cancers are known to be driven by mutations in genes like EGFR in some lung cancers. Identifying these genetic alterations allows doctors to prescribe targeted therapy drugs that are designed to block the pathways these mutations activate.
This level of detailed analysis is a cornerstone of precision medicine, which aims to tailor treatment to the individual patient. By understanding the molecular drivers of a specific cancer, clinicians can select therapies that are most likely to be effective. It also opens the door for immunotherapies, which are treatments that harness the patient’s own immune system to fight the cancer.
Determining Cancer Staging
Cancer staging is the process of synthesizing all available diagnostic information to describe the extent of the cancer within the body. It provides a comprehensive picture of the tumor’s size and how far it has spread from its original location. This summary is fundamental for determining the most appropriate treatment strategy and for understanding a patient’s prognosis.
The most widely used staging system is the TNM system. Each letter represents a different aspect of the cancer’s progression. “T” stands for the primary tumor and describes its size and whether it has grown into nearby tissues. The pathology report provides the definitive “T” value based on the microscopic examination of the surgically removed tissue.
“N” refers to the spread of cancer to nearby lymph nodes. The pathologist’s analysis of removed lymph nodes determines the “N” value, indicating if cancer is present in the nodes and how many are affected. The “M” component stands for metastasis, signifying whether the cancer has spread to distant organs. While pathology can sometimes identify metastasis if a sample from a distant site is biopsied, the “M” status is often determined through imaging tests like CT, PET, or MRI scans.
The combination of the T, N, and M values results in an overall stage, typically expressed in Roman numerals from I to IV. Stage I cancers are generally small and localized, while Stage IV indicates that the cancer has metastasized to other parts of the body. Some cancers may also be classified as Stage 0, which describes an early, non-invasive condition. This final stage provides a universal language for doctors to understand the scope of the cancer and plan the best course of action.