Mesothelioma Pathology

Mesothelioma pathology is part of the process for a mesothelioma diagnosis. It is the next step following a biopsy and examines tissue or fluid samples.

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Written by Jenna Campagna, RN

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Important Facts About Mesothelioma Pathology

  • Mesothelioma pathology is the study of tissue or fluid samples for the presence of mesothelioma. Doctors look for mesothelioma biomarkers or diseased mesothelial cells.
  • Pathologists perform tests, either histology or cytology, on samples. Histology tests tissue and cytology tests fluid.
  • Pathology reports include pertinent information about the samples, diagnosis, cell type and more.
  • Mesothelioma pathology helps doctors determine the cell type. This reveals more about the prognosis.

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 mesothelioma diagnostic process begins with imaging tests. Doctors look for abnormalities in scans, which 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 to extract tissue or fluid from wherever doctors believe the disease exists. Following the biopsy, the surgeon sends the tissue or fluid samples to a pathologist, who examines it. They’ll create a pathology report about the findings.

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 samples.

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

Calretinin

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 are the descriptions of the tissue or fluid samples and 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 within pathology testing and reports. Which one your pathologist performs depends on whether you undergo a tissue biopsy or have fluid removed.

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Cytology

Cytology is the study of cell structure and cells’ functions. This term can be interchangeable with cytopathology, which is 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 fluid buildup in either the pleura or the peritoneum. Pathologists then stain the fluid to see if malignant cells react to the stain.

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

However, a definitive diagnosis using 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 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 mesothelioma pathology.

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Histology

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

For mesothelioma, pathologists conduct histology testing by examining extracted tissue for malignancies. 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 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 doctors to determine the mesothelioma cell type. This can affect the patient’s treatment options and mesothelioma prognosis.

Determining the Mesothelioma Cell Types

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

Epithelioid Cell Icon

Epithelioid

Epithelioid mesothelioma is the most common cell type of this cancer. The characteristics include a clearly defined egg shape with a visible nucleus and pink cytoplasm. Epithelioid mesothelioma is the most treatable cell type because they tend to stick together and are easier to remove surgically.

Sarcomatoid Cell Icon

Sarcomatoid

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

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Biphasic

Biphasic mesothelioma is a combination of epithelioid cells and sarcomatoid cells. It is the second most common mesothelioma cell type. The cancer must have at least 10% of each cell to be biphasic mesothelioma. Treatment and prognosis depends on which cell type is more prevalent. Patients with more epithelioid cells than sarcomatoid cells 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: March 22, 2021.

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