Histology of Mesothelioma

Histology is the study of tissues and cells under a microscope. Histological analysis of malignant tissue is an invaluable tool in diagnosing a patient's mesothelioma, as well as monitoring the progress of various types of treatment. A subsection of histology that more accurately defines examination of cancer cells is histopathology, which is defined as the study of diseased tissue under a microscope.

The Role of Histology in Cancer Diagnosis

While outwardly visible symptoms may indicate cancer, a histology report is necessary to verify every mesothelioma diagnosis. Histologists use tissue samples collected from a patient to identify the presence of cancerous cells; the collection is a process known as biopsy. For some types of cancer, biopsy tissue can be obtained through surgery, endoscopy, or skin sample collection, but mesothelioma (and some other cancers) are almost always diagnosed with a needle biopsy in which a syringe is used to collect cells from the mesothelium.

The presence of a tumor does not necessarily indicate cancer. In fact, most tumors in the body are not cancerous. Although rare, there is such a thing as benign mesothelioma. To determine the cellular basis of these tumors and whether or not they are cancerous, a histological report must be performed.

Once the biopsy is acquired, the tissue sample is placed in a preservation liquid called formalin. The specimen is sealed, labeled, and then transferred to a pathology lab. At the lab, the sample is reviewed without the help of a microscope. Basic features of the sample, including size and color may be recorded. Some of these outwardly visible features may hint at a specific type of cancer and help the histologist narrow down possible cancer types.

After visual inspection, the biopsy is processed and inserted into a mold with hot paraffin wax. When this wax cools, the specimen is locked in place and protected from contamination. Thin slices of this wax are then cut and placed under a microscope for inspection. To improve visibility of the cell tissue, various types of dye may be applied.

After this preparation process is completed, the histologist views the specimen with the help of a microscope. The histologist will be looking for unique characteristics of cancer cells in order to verify a cancer diagnosis. Different types of cancer exhibit unique cellular characteristics that usually allow for diagnosis of an exact cancer type.

Specialized Histology Stains

Specialized histology stains can further aid the histologist in diagnosis. Histochemical stains are designed to attract and bind to specific substances that are over-exhibited in unique types of cancer cells. For example, adenocarcinomas produce mucus. To more easily identify this bi-product, a stain that is attracted to mucus (mucicarmine stain) is used.

Immunihistochemical stains take advantage of antibody/antigen binding properties to only alter the color of those cells in which binding occurs. Since certain antibodies are only present in cancer cells, this can help distinguish between healthy and unhealthy cells. Immunihistochemical stains are used to distinguish between sarcomatoid and epithial mesothelioma cell types. This information is important to the oncologist planning a treatment regimen.

Histology Characteristics of Cancer Cells

Pathologists can look for several broad features that are indicative of cancer cells. These include:

  • Abnormal size: cancer cells are usually either larger or smaller than healthy cells
  • Abnormal nucleus: The nuclei of cancer cells are often larger and darker than healthy cells (this is due to an overproduction of DNA)
  • Disorderly arrangement: cancer cells may order themselves in a more disorderly fashion than healthy cells

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