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Mesothelioma Pathology

Pathology is the study of how a disease progresses and how it manifests in the body. A pathologist studies diseases, but can also be a useful diagnostician because of his or her knowledge of a disease. This medical professional can look at scanned images, biopsies, cells, and blood of a person who might have mesothelioma and give an informed opinion or contribute to a diagnosis.

Different diseases, and even different types of cancer, leave telltale signs in a person’s body, in the symptoms that person experiences, an even in the blood and cells of that patient. The pathology of mesothelioma and is a crucial part of an accurate diagnosis.

The Pathology of Tumor Growth

Looking at the anatomy of the cancer, or how the tumors grow and develop in the body, is one way of diagnosing mesothelioma. The most obvious anatomical sign of mesothelioma is the thickening of the pleural space, the lining of the lungs. Additionally the tumor may develop small nodules over the surface of the pleura and in other similar areas. This may include on the diaphragm.

Pathologists have described rare cases of localized malignant mesothelioma. This presents as a single mass instead of the characteristic pleural thickening plus nodules.

The more common nodules characteristic of mesothelioma usually range in size from as small as one millimeter to as large as one centimeter. As the cancer advances the nodules and tumors form plaques. These develop into thick tissue that encases and interferes with organs, usually the lungs.

Metastasis or the spread of cancer cells from the primary location, is another sign of advanced mesothelioma. With pleural mesothelioma the cancer often spreads to skeletal muscle in the chest cavity, deep layers of the skin, the diaphragm, organs of the abdominal cavity, and finally the lymph nodes. In peritoneal mesothelioma, the tumor often spreads to the liver, spleen, intestines, and other abdominal organs.

Histology: Pathology of Cells

Pathologists look at macrostructures like organs, but also at microscopic structures like cells to investigate how mesothelioma develops. Histology is the study of the pathology of cells. Mesothelioma is a difficult cancer to diagnose just by the macrostructure of the tumor. Looking at the cells is also important, but even then it is not easy to determine if the cancerous cells are from mesothelioma or another cancer, like lung cancer.

A biopsy must be done to extract cells from a tumor; those cells will then be examined under a microscope to look for characteristic signs of mesothelioma. Pathologists use certain stains to identify chemicals and structures within and on the surfaces of cancer cells from a biopsy sample. There are four distinctive types of cells that can be seen in a sample from a mesothelioma tumor:

  • Cells that may be cube, oval, or polygonal in shape and mimic non-cancerous cells of the mesothelium. This accounts for most cases of mesothelioma, another reason it is hard to diagnose.
  • Cells shaped like spindles that mimic the cells found in lung cancer. This is yet another reason mesothelioma is difficult to diagnose.
  • In biphasic mesothelioma tumors there are cells both of the epithelioid and sarcomatoid types.
  • Cells that resemble those found in a condition called fibrous pleuritic. Distinguishing between the two is very difficult.

Cytology, another type of histology, can be used on the cells found in fluids. This requires a less invasive biopsy. Usually a simple needle biopsy to extract fluid from the area around the tumor or around the pleura is adequate. Cells from the fluid can then be quickly examined to determine if malignant cells are present. The technique is quick and inexpensive, but it cannot tell if a malignancy is the original tumor or one that spread from the original location. Confirmation of cancer with cytology is usually then backed up with a more extensive histology study.

Some of the characteristics that cytology tests look for in mesothelioma cells include large balls of cells, resembling the structure of a berry. The cells in these bundles are usually larger than those in healthy mesothelium. Atypical features in the nucleus of a cell are also characteristic of mesothelioma, as is the presence of structures called macronulcleoli.


Pathologists can also use immunohistochemistry to identify cancer cells of the mesothelium. This is one of the most accurate, although not foolproof, ways to distinguish between mesothelium cancer cells and other types of cancer cells. Immunohistochemistry uses antibodies, proteins of the immune system that detect pathogens, to detect the proteins, called antigens, that are characteristic of a particular type of cancer cell.

To see the antibodies and to detect the antigens, they are typically stained or attached to fluorescent dye. As the antibodies attach to antigens specific to mesothelioma, they become visible. If they do not attach, the stain or dye is not activated and the presence of mesothelioma is not confirmed. An immunohistochemistry test is often required in legal cases of asbestos-caused mesothelioma to confirm the diagnosis.

Pathology is important to the study of all diseases. It helps with diagnoses, but also in understanding how a disease like mesothelioma progresses. Knowing more about a disease and how it affects the body helps to inform better treatments. For someone that may have mesothelioma, using pathology techniques to make a better diagnosis is crucial. This cancer is already difficult to pinpoint, so using advanced and detailed pathology helps make a more accurate diagnosis sooner.

Page Edited by Dave Foster

Dave has been a mesothelioma Patient Advocate for over 10 years. He consistently attends all major national and international mesothelioma meetings. In doing so, he is able to stay on top of the latest treatments, clinical trials, and research results. He also personally meets with mesothelioma patients and their families and connects them with the best medical specialists and legal representatives available. Connect with Patient Advocate Dave Foster

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