Mesothelioma histology is a pathology process used to diagnose this rare and aggressive cancer. Doctors look at tissue samples under a microscope to determine if cells have mutated and formed into mesothelioma.
Written by Jenna Campagna, RN
What Is Mesothelioma Histology?
Mesothelioma histology, or mesothelioma histopathology, is the study of tissue for the presence of mesothelioma. This process is part of mesothelioma pathology, which involves examining either tissue or fluid to determine if this cancer exists in the body.
The medical term “histology” refers to the microscopic study of tissue. “Histopathology” is the inspection of tissue for diseased cells. These two terms are interchangeable when referring to the process used for diagnosing mesothelioma.
The most notable characteristics of mesothelioma histology are:
- Most definitive method to diagnose mesothelioma
- More reliable than studying fluid samples (mesothelioma cytology)
- Can be accomplished with a large or small incision
- More invasive process needed to extract tissue than to remove fluid
- Larger number of cells to analyze in tissue samples compared to fluid
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How Is Mesothelioma Histology Performed?
Mesothelioma histology is one of the final steps in the diagnostic process for this cancer. Histology starts with extracting tissue from the body during a mesothelioma biopsy.
Doctors remove tissue samples from patients due to:
- The patient experiencing mesothelioma symptoms
- Imaging tests showing visual signs of the cancer
- Blood tests suspecting the presence of mesothelioma
How Are Tissue Samples Collected?
Doctors collect tissue samples for mesothelioma histology through biopsy procedures. One option is a surgical biopsy, which involves a large incision and possibly anesthesia. However, due to improvements in medical technology and practices, most doctors use a camera-assisted needle biopsy to extract tissue. This method makes a small incision.
There are multiple types of mesothelioma biopsy procedures, and each applies to diagnosing different types of mesothelioma. The tissue biopsy you’ll undergo depends on where doctors believe your mesothelioma originated — or where it has spread to. The mesothelioma biopsies used to remove tissue are:
Thoracotomy — Involves opening the chest cavity and removing tissue from the thorax, specifically the pleura, to diagnose pleural mesothelioma
Laparotomy — Involves opening the abdominal cavity and removing tissue from the abdomen, specifically the peritoneum, to diagnose peritoneal mesothelioma
Thoracoscopy — A camera-assisted needle biopsy used to remove tissue from the pleura and diagnose pleural mesothelioma in a less-invasive manner than a thoracotomy
Laparoscopy — A camera-assisted needle biopsy used to remove tissue from the peritoneum and diagnose peritoneal mesothelioma in a less-invasive manner than a laparotomy
Mediastinoscopy — Involves opening the chest to remove lymph-node tissue from the mediastinum, which is the small space between your lungs, if doctors believe tumors have spread to the area and affected lymph nodes
After your doctor takes a tissue biopsy, they’ll request a pathology report to declare a definitive mesothelioma diagnosis.
Pathology reports are the results of mesothelioma histology tests, which involve microscopic observation of the tissue samples. These tests are the most important and conclusive factor in determining a patient’s diagnosis — and classifying their cell type and stage.
How Do Doctors Test Tissue Samples?
After collecting the samples, pathologists study the tissue under a microscope to determine if mesothelioma is present. They’ll also examine the tissue for specific characteristics that reveal the mesothelioma cell type, among other traits.
In determining cell type, pathologists look for:
- Cellular behavior
- Cell size and shape
- Cell nuclei
- Cell pattern of the sample
Each cell type — epithelioid and sarcomatoid — has unique characteristics. Epithelioid mesothelioma cells are well-defined, with a visible nuclei, and clump together. They also grow quickly but metastasize slower than sarcomatoid cells do.
Sarcomatoid mesothelioma cells are less defined and tougher to identify. They have an irregular shape and elongated structure. Sarcomatoid cells also spread faster and don’t appear as clumped together.
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Immunohistochemistry in Mesothelioma Histology
Doctors test tissue samples to detect mesothelioma through the process of immunohistochemistry, which is an integral part of mesothelioma histology. This method can provide evidence of mesothelioma tumors that supplements with the pathologist’s microscopic examination of the cells.
Immunohistochemistry requires immunohistochemical staining, which involves introducing a foreign substance to the tissue samples. The foreign substance is an antibody that reacts with mesothelioma cells and reveals their presence.
There isn’t one particular antibody that presents a positive immunohistochemical stain for mesothelioma. Therefore, pathologists must conduct multiple tests with various antibodies.
Staining can also help pathologists determine which cell type comprises the patient’s disease. Some mesothelioma cell types respond to specific antibodies used in staining. The most common positive stains for pleural mesothelioma are:
Calretinin — Indicated in close to all cases of epithelioid mesothelioma
Cytokeratin 5 or 5/6 — Shown in between 75% and 100% of diagnoses
Wilms’ tumor-I antigen (WT1) — Expressed in between 70% and 95% of cases
Podoplanin (D2-40) — Exhibited in between 90% and 100% of diagnoses
Other positive stains used to detect sarcomatoid mesothelioma cells include AE1/AE3 and CAM5.2.
Mesothelioma Histology Accuracy and Seeking the Help of a Specialist
Mesothelioma histology is more trusted than cytology for pathologically diagnosing this disease. This fact is due to tissue samples being more reliable than fluid samples.
One study published on UpToDate compared the accuracy of tissue biopsies and fluid samples:
- Camera-assisted tissue biopsies were 98% accurate in diagnosing mesothelioma in cases when this method was used.
- Fluid biopsies were only 26% accurate in diagnosing mesothelioma when this method was used.
Mesothelioma misdiagnosis is common due to this cancer being so aggressive and expressing symptoms common with many other illnesses. Mesothelioma is also rare, and many pathologists do not have experience studying and identifying mesothelioma cells under a microscope.
If you believe you may have mesothelioma, you should get input from a specialist. They will utilize pathologists who have experience detecting this cancer and performing mesothelioma histology. We can help you connect with some of the top mesothelioma specialists across the country to begin the diagnostic process.
Last Edited: July 10, 2020.