Understanding Cancer Diagnosis through Tissue Sample Examinations by Pathologists

Introduction to Cancer Diagnosis

Diagnosing cancer often involves examining tissue samples under a microscope, a process overseen by skilled pathologists. This method, known as histopathology, plays a crucial role in determining the presence, type, and stage of cancer. Doctors do not typically examine samples directly for diagnostic purposes; rather, they assess the prepared slides to identify characteristic structures and features that indicate the presence of cancerous changes.

The Biopsy Process and Pathological Analysis

The most common scenario in a cancer diagnosis begins with the discovery of a mass, which can be detected via physical examination, radiologic imaging, or other diagnostic methods. A healthcare provider, often a surgeon, radiologist, or health care professional, will remove a portion, or even the entirety, of the mass through surgical excision or biopsy. The removed tissue is then fixed in a preservative like formalin and sent to a pathology lab for further analysis.

Gross Examination and Tissue Embedding

In the lab, a gross description of the tissue is dictated. Then, portions of the tissue selected by the pathologist or his/her assistant undergo an overnight process to completely remove all water and embed it into small paraffin blocks. This process allows for the creation of extremely thin slices (4-8 microns) that are placed on a glass slide. These slices are then stained with hematoxylin and eosin (HE), which reveal cellular structures more clearly under the microscope.

Microscopic Analysis by Pathologists

The pathologist examines the stained slides under a microscope, focusing on the characteristics of the cells. This includes the arrangement of cells to form tissue structures, the size and shape of individual tumor cells, and the appearance, size, shape, and density of the cell nuclei. Additional features noted include the number of mitoses (a measure of the growth rate of the tumor), the degree of necrosis (dead cells), and the connections between individual cells.

Immunohistochemical Stains and Differentiation

When the tumor cells do not resemble the tissue from which they originated, immunohistochemical stains are utilized. These stains help determine the type of tumor, especially for poorly differentiated tumors, where the tumor cells do not closely resemble the normal tissue. For example, a well-differentiated squamous cell carcinoma may have cells resembling the squamous cells of the bronchial lining, while a poorly differentiated large cell tumor may not. A positive immunohistochemical stain for keratin indicates a squamous cell origin.

Importance of Classification and Staging

Classifying the type of tumor and staging the tumor (determining how advanced it is and how large it has grown, as well as if and where it has metastasized) are crucial for determining the appropriate treatment. Different tumor types respond differently to chemotherapy or radiation. Well-differentiated tumors, which resemble the host tissue more closely, are usually lower grades and grow more slowly. Poorly differentiated tumors, which do not resemble the host tissue, are higher grades and are generally more aggressive.

Pathologic Prompting

During surgery, a rapid "frozen section" pathologic diagnosis may be made. This involves sending the tissue sample immediately to the pathology lab without preservative treatment. The pathologist quickly dictates a gross description, freezes a selected sample, and runs a similar but more rapid process of fixation and staining. Immediate microscopic examination and diagnosis can help determine the extent of the surgery or whether the tumor has been adequately sampled or removed, potentially saving the patient from a second surgery.

Conclusion

Understanding the sophisticated process of examining tissue samples under a microscope is essential for accurate cancer diagnosis and treatment. By analyzing the characteristics of cells and tissues, pathologists can provide critical information for determining the type and stage of cancer, guiding treatments and prognosis.