Mesothelioma Histology
Cancer specialists can uncover important microscopic
features of your disease with the science of histology. These features
play an important role in diagnosis, treatment and your life expectancy.
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Histology is a branch of biology and medicine that involves the study
of the cells and tissues of animals and plants. Samples of tissue are
stained on a slide and observed under a microscope to study the
structure and composition of each cell. Because mesothelioma histology
involves the study of cancerous mesothelial cells, it is considered a
branch of histopathology, which is the study of diseased cells. Trained
medical doctors, usually board-certified pathologists, examine the tumor
tissue under a microscope and classify cells by type.
Histopathology is within the larger field of pathology,
which studies the nature, cause and effect of diseases. Pathologists
are highly trained medical professionals who examine tissue samples to
get an accurate diagnosis, and they’re assisted by histotechnicians and
histopathologists, who help with tissue staining to identify diseased
cells.
There are several types of mesothelioma cancer cells. Each cellular
type responds to different treatments and affects the individual
patient's prognosis, so an accurate diagnosis
of cancer cell type is essential to develop an effective treatment
plan. After treatment is administered, studying tissue samples can also
provide insight on the effectiveness of chemotherapy drugs and other
treatments.
Histology also helps prevent mesothelioma misdiagnosis.
For example, peritoneal cancer in women and ovarian cancer can be
difficult to differentiate without analyzing the cell type through
histopathology. If patients are pursuing legal action against an
asbestos-producing company that may have caused their cancer, a
misdiagnosis can also negatively affect their chances of obtaining
compensation.
Cell Types
When specifically examining a tumor sample for the presence of mesothelioma, a histopathologist will carefully inspect the sample for three types of cells:
These spindle-shaped sarcomatoid
cells typically lack strong characteristics and occur in approximately
10 to 20 percent of reported cases. While they are the most aggressive
cell type, they are also the least common.
Malignant mesothelioma is considered biphasic
when both epithelial and sarcomatoid cells are present and each type
accounts for at least 10 percent of the tumor's mass. Biphasic (mixed)
cells are present in 20 to 35 percent of all mesothelioma cases.
Dr. Fontaine explains how does mesothelioma cell types affect a patients treatment options.
Cell Types
Of all subtypes, tumors involving epithelial cells are typically most responsive to treatment, which often leads to a better prognosis. Because sarcomatoid cells are the most resistant to treatment, some surgeons do not consider sarcomatoid tumors eligible for surgery. The biphasic cell type is also considered less responsive to treatment than epithelial.
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Characteristics of Malignant Mesothelioma Cells
Each specific cell type has different visible characteristics. For example, sarcomatoid cells have elongated nuclei, while epithelial cells are most commonly distinguished by the identification of microvilli (microscopic protrusions of a cell) or cell organelle.The characteristics noted in the different cell types are very subtle. Unfortunately, this can make the diagnosis process quite challenging. Specifically, distinguishing mesothelioma cells from adenocarcinoma cells, a cancer that affects glandular tissue, can be a serious challenge because the cells can appear similar.
Fast Fact: Frozen section
fixation is a histology process where a surgically removed tumor is
quickly frozen. A slice of the frozen tissue is stained and placed on a
slide to determine if a tumor is malignant, usually while the patient is
still in surgery.
Rare Variances in Histological Mesothelioma Types
- Deciduoid
- Desmoplastic
- Lymphohistiocytoid
- Small Cell
Next Type
The Histology Process
Before a diagnosis of cell type is made, tissue samples are
obtained and prepared for study. Teams made up of surgeons,
histotechnicians, histopathologists and other professionals work
together to provide a patient's doctor with information.
When testing for mesothelioma, a medical test involving the removal and examination of cells,
tissue or fluids from the body, known as a biopsy, is often performed.
After the biopsy, the tissue is prepared by specialists called
histotechnicians. These scientists process the tissue by preserving it
and staining it with a number of special chemicals that will reveal the
minute structures of the cells. They also observe the size, shape and
anatomical structure of cells, which helps identify the cell type.
How Histotechnicians Prepare a Tissue Sample for Staining
Fixing
Makes the tissue more rigid and allows for easier slicing. The tissue is placed in a chemical like formaldehyde.Sectioning
Takes place in a machine called a microtome. The microtome can slice extremely thin pieces of the sample.Embedding
The tissue is embedded in a block of paraffin or plastic resin to make the material easy to cut.Mounting
After the slices of embedded tissue are smoothed out in a water bath, they are placed on slides and baked to set the paraffin.
After the cancerous tissue is mounted
and stained on a slide, the specimen is now ready for study. Then,
histopathologists take the slide and view it under a microscope. They
can determine what type of cancer may be present by viewing the
structure of cells in the tissue.
In addition to staining, histotechnicians may choose to use
different techniques for highlighting the details in cells that may be
of interest, such as in situ hybridization and immunohistochemistry. In
situ hybridization uses the application of fluorescent or radioactive
probes to bind DNA and RNA and analyze the genes of a cell. Using this
method, scientists can detect genetic abnormalities present in the
cells.
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Immunohistochemistry
Immunohistochemistry is based on the principle that antibodies
bind to specific antigens and proteins called oncoproteins in human
tissue. Different antibodies are applied to tissues on a microscope
slide. The tissue samples are then analyzed for specific visual patterns
created by the interaction of antibodies and proteins.
Immunohistochemical staining is widely used in the diagnosis
of mesothelioma cells and other abnormal cells. However, many medical
experts say that immunohistochemistry should be used in context with
other diagnostic data. In other words, the results of an
immunohistochemistry analysis should not be considered the primary
indicator for a mesothelioma diagnosis.
However, other studies have found that immunohistochemical
stains improve the accuracy of diagnosis. In one Japanese study, it was
estimated that 10 to 15 percent of patients received an inadequate
diagnosis. Since many patients require this diagnosis for legal action,
the study recommended improving current diagnostic techniques by
improving the quality of immunohistochemistry stains.
Two antibodies often used to aid in diagnosis are BerEP4 and
vimentin. BerEP4 is helpful in the diagnosis of epithelial
mesotheliomas. However, immunohistochemists are still researching the
efficacy of BerEP4 as a diagnostic indicator, because this antibody has
appeared both in mesotheliomas and other similar tumors.
Like the antibody BerEP4, vimentin helps diagnose mesothelioma,
but the protein also appears in other tumors. Because vimentin appears
in other malignant tumors, it is not considered a discriminatory marker
for mesothelioma, but rather a piece of the diagnostic puzzle.