Receiving a mesothelioma diagnosis, or any cancer diagnosis for that matter, is more complex than simply knowing the basic type you have. In addition to determining where the cancer originated (pleural, peritoneal or pericardial mesothelioma), the oncologist will also determine the cell type and learn more about how your particular case is expected to develop.
To do so, doctors rely on two very closely related fields: mesothelioma histology and cytology.
What’s the Difference Between Histology and Cytology?
Determining the mesothelioma cytology and histology for an individual go hand-in-hand, as the two fields overlap and complement one another.
Histology is the study of the function and structure of anatomy. This includes observing the tissues, cells, organs and organ systems of the body. When thinking of mesothelioma histology or histology of any cancer, researchers typically refer to the type of tissue in which the cancer originates.
There are hundreds of histological types for cancer, which are divided into a few categories based on the tissue where the cancer originated and the cell type observed in the tissue sample. For instance, one category looks at the epithelial tissue, meaning cancer in the internal or external lining of the body. Mesothelioma could fall under this category as each type originates in the lining of different organs, like the lungs or the abdominal cavity.
Cytology, on the other hand, relates to the study of the cells, including their structure, function and chemistry. Whereas histology samples will generally be tissue biopsies, cytology samples may also be taken from fluids in the body, like pleural fluid or peritoneal fluid buildup that can occur with mesothelioma and other conditions. Some better known examples of cytology are screenings for other cancers and health concerns, like the Pap test. Analyzing with cytology will also focus on how the malignant mesothelial cells are grouping together or isolated in the body.
Overall, both of these fields are an important aspect of diagnosing mesothelioma, as well as determining next steps like treatment.
How Mesothelioma Cytology and Histology Work Together
Mesothelioma histology and cytology are both important, and laboratory technicians use both techniques to determine a patient’s cell type and how the cancer cells are grouping in the body. Together, malignant mesothelioma cytology and histology are important for understanding how an individual’s case can be expected to react to treatment, how the cancer may spread and develop, and determine a patient’s prognosis.
Mesothelioma histology describes the cell type found in the patient’s tumors and the tissue where the cancer originated. For mesothelioma patients, there are three basic cell types expected: epithelioid, sarcomatoid and biphasic. The cell types differ in shape of the cell itself and its nuclei, behavior and growth patterns. Epithelial cells, for instance, are elongated with visible nuclei. These cells are more likely to form in clusters and stay together, which means a slower metastasis in the body. However, the cells do divide and grow quickly. The epithelial type is most common in pleural or peritoneal mesothelioma.
Sarcomatoid cells can be more difficult to differentiate. They have a spindle-shape with an elongated nucleus, and sometimes even have multiple nuclei in one cell. Unlike epithelioid cells, these do not often form in clusters or stick together, making for faster, dangerous spreading. Sarcomatoid cells, though rare, are considered to have the worst prognosis because of the rapid spreading and growth. The last cell type, biphasic, is a mixture of epithelial and sarcomatoid cells, so can have varied survival depending on which cell type is dominant.
When further exploring the malignant mesothelioma cytology, researchers will more closely examine the cell’s shapes and nuclei, the sizes of the cancerous cells and how the cells are grouping together. The cytologic analysis also explores the patterning of the tumor cells. This data can help differentiate a mesothelioma cells from adenocarcinoma cells, as mesothelioma can often be confused for this and other types of cancer.
The cytologic diagnosis will also determine if the patient has malignant cells or benign mesothelial cells. Though benign mesothelioma is extremely rare, only having been reported in about 200 cases, it is possible some patients may begin with benign tumors. Since these can become malignant, treatment is still important to remove the tumors as early as possible. Malignant, or cancerous, cells are more common with mesothelioma, and determining the exact cell type and the complexities of how the tumor cells are forming and reacting in the body is essential for extending survival.
Some of the cytologic features doctors will observe include:
- Cell blocks (how the cancerous cells cluster together in sections)
- Large clusters of single cells and the shape of such formations
- Cytomegaly (the enlargement of cells)
- Nuclear pleomorphism (variability in the size, shape and staining of cells or nuclei)
- N/C ratio, the ratio of nucleus to cytoplasm, is normal (a high ratio shows malignancy)
- Any nuclear atypia (abnormalities in the cell nuclei, which also indicates malignancy)
All of this specific information on the cell type and how they have manifested in the body creates a clear picture of a patient’s individual disease, prognosis and how treatment should be approached.
The Importance of Cell Typing
Together, histology and cytological diagnosis can help mesothelioma doctors in a number of ways. These medical fields can help overcome the diagnostic challenge of properly detecting mesothelioma. Analyzing the disease on a cellular level can help differentiate mesothelioma from other types of cancer and diseases, as well as fully classify the type of mesothelioma the patient is facing.
By fully understanding how the tumor cells are growing and reacting, doctors will have a better chance of formulating an effective, personalized treatment plan. Many even refer to cell typing and truly analyzing the characteristics of the malignant cells as the best way to predict survival.
Image Credit: Ed Uthman, Small cell lung carcinoma vs. benign mesothelial cells