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Mesothelioma Pathology

Mesothelioma pathology is part of the process used to issue a mesothelioma diagnosis. It is the next step following a biopsy and is used to examine tissue or fluid samples.


Written by Jenna Campagna, RN


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What Is Mesothelioma Pathology?

Mesothelioma pathology is the study of tissue or fluid samples to determine if mesothelioma is present, along with specific characteristics of the disease. Pathologists conduct the mesothelioma pathology process.

The process of receiving a mesothelioma diagnosis begins with imaging tests. Doctors look for abnormalities in scans, which can indicate the presence of this cancer. However, the only definitive way to diagnose mesothelioma is through a biopsy.

A mesothelioma biopsy is a medical procedure that involves extracting tissue or fluid from the area where doctors believe the disease exists. Following the biopsy, the surgeon sends the tissue or fluid samples to a pathologist, who examines it and creates a pathology report.

Immunohistochemical Staining in Mesothelioma Pathology

Part of mesothelioma pathology is immunohistochemical staining, which helps pathologists determine if mesothelioma is present. This scientific practice also reveals which cell types are present in the tissue or fluid samples.

Staining reveals antibodies or proteins, also called “immunohistochemical markers.” The immunohistochemical markers for pleural mesothelioma include:


Demonstrated in nearly all epithelioid mesothelioma cases

Cytokeratin 5 or 5/6

Expressed in between 75% and 100% of cases

Wilms’ tumor-I antigen (WT1)

Shown in between 70% and 95% of diagnoses

Podoplanin (D2-40)

Demonstrated in between 90% and 100% of cases

What Is on a Mesothelioma Pathology Report?

There are multiple sections to a mesothelioma pathology report, which can be long and complex. The most essential parts of the report are the descriptions of the tissue or fluid samples, and then the diagnosis section.

The sections of a mesothelioma pathology report include:

  • Identifying information — The patient’s name, date of the biopsy, lab number of the specimen sent for testing and more
  • Clinical information — Medical history of the patient or special notes related to testing
  • Gross description — The pathologist’s findings from looking at, measuring or feeling the sample without the aid of a microscope (usually related to size, shape, color and consistency)
  • Microscopic description — The pathologist’s findings after looking at the sample through a microscope (usually related to appearance of cells, extent of tumor invasion and histochemical staining results)
  • Diagnosis — The pathologist’s answer to whether or not the patient has cancer, including which type


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Types of Mesothelioma Pathology

This report is based on data compiled from either a histology test or a cytology test (or both). Histology and cytology are separate medical terms that make up pathology testing and reports. Which one your pathologist performs depends on whether you undergo a tissue biopsy or get fluid samples removed.

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Cytology is the study of cell structure and cells’ functions. This term can be interchangeable with cytopathology, which refers to the examination of diseases at the cellular level.

In the case of studying mesothelioma, pathologists analyze fluid samples to learn more about the potential presence of malignant cells. Doctors use a needle to extract a sample of the fluid that has built up in either the pleura or the peritoneum. Pathologists then stain it to see if there are malignant cells that react to the stain.

Mesothelioma cytology involves a less-invasive diagnostic procedure than a tissue biopsy. Doctors will not need to make a large incision or use a thick needle to remove fluid.

However, making a definitive diagnosis with fluid samples is challenging. There are often not enough malignant cells in the sample to determine if a patient has mesothelioma. Pathologists also have difficulty analyzing the cells that are provided in the sample.

“It’s harder to examine the architecture of the individual cells suspended in the fluid,” said Dr. Elliot Wakeam, a thoracic oncologist at Michigan Medicine.

For these reasons, many mesothelioma doctors and pathologists prefer tissue samples and histology for the mesothelioma pathology process.

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Histology is the study of tissue under a microscope. The term can be interchangeable with histopathology, which is the study of diseases present in tissue.

For mesothelioma, pathologists conduct histology testing by examining tissue extracted from someone who may have malignant cells. Doctors retrieve this tissue one of two ways: from a surgical biopsy, which involves a large incision; or from a needle biopsy, which requires a small incision.

Histology can be done in unison with cytology testing to study both tissue and fluid samples. However, tissue samples provide more conclusive evidence of whether or not mesothelioma is present. The tissue usually provides more cells to study, and the cells are easier to examine without fluid present.

Pathologists stain these cells to uncover the presence of cancer. This staining also allows the doctors to determine which mesothelioma cell type is primary. This knowledge can affect the patient’s treatment options and mesothelioma prognosis.

Determining the Mesothelioma Cell Types

One of the main reasons to get a mesothelioma pathology report is to determine the exact cell type of a cancer. Mesothelioma tumors can be made up of three cell type variations, each with their own unique qualities and effects on the patient’s prognosis.

Epithelioid Cell Icon


Epithelioid mesothelioma is the most common cell type of this cancer. The characteristics of these cells include a clearly defined egg shape with a visible nucleus and pink cytoplasm.

Sarcomatoid Cell Icon


Sarcomatoid mesothelioma is the least common cell type of this cancer. Sarcomatoid mesothelioma cells are spindle-shaped, often overlap one another and show multiple elongated nuclei. Sarcomatoid cells spread quickly throughout the body since they do not stay clumped together.

Biphasic Cell Icon


Biphasic mesothelioma is a combination of epithelioid cells and sarcomatoid cells. It is the second most common mesothelioma cell type. The cancer must include at least 10% of each cell to be classified as biphasic mesothelioma. Treatment and prognosis depends on which cell type is more prevalent. Patients with more epithelioid cells than sarcomatoid cells typically have longer life expectancy.

Common Questions About Mesothelioma Pathology

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What is the job of a mesothelioma pathologist?

Pathologists analyze tissue and fluid samples extracted from biopsies. Mesothelioma pathology explicitly tests these samples for diseased mesothelial cells, which can form clumps called tumors. Pathologists examine cells under a microscope and use a staining process to detect cancerous proteins specific to mesothelioma.

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What information is included in a mesothelioma pathology report?

The pathology report includes the patient’s name and other identifiable information, medical history, the pathologist’s description of the biopsy sample without using a microscope, the microscopic characteristics and the diagnosis.

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Why is pathology important for mesothelioma?

Pathology is the scientific process to determine if the sample removed from a biopsy includes mesothelioma. Pathologists are integral to properly diagnosing this disease. Pathology also can determine the cell type and stage of the cancer.

Last Edited: October 28, 2020.

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