Histology refers to the scientific study of the minute structure of plant or animal tissues. Therefore, mesothelioma histology is the study of the anatomy of the disease at the cellular and molecular levels to better understand exactly how it forms and what cell interactions lead to the consequences of the disease including effusion and tumor growth. Mesothelioma is most commonly referred to by its location – pleural, peritoneal or testicular. However, mesothelioma can also be identified by its histology – the anatomy of the types of diseased cells. Histology involves a very precise and in-depth study of the cells which analyzes various characteristics such as size, shape, nuclei, and protrusions.
Histology is very important to a mesothelioma diagnosis for a couple of reasons. First, by correctly diagnosing the type of mesothelioma cells, doctors are better able to determine the best treatment option. Second, researchers are better able to use case studies to determine the most beneficial direction to take in their efforts to improve diagnosis and treatments.
Currently, there are three main types of mesothelioma cells: epithelial, sarcomatoid, and biphasic.
Epithelial mesothelioma is the most common mesothelioma cell type. Though the estimated numbers of incidences can vary depending what reference is used, the epithelioid mesothelioma variant represents between 50 to 75 percent of all diagnosed mesothelioma cases. Epithelial cells are the cells that compose the membrane covering internal organs and lining the chest and abdomen cavities.
Epithelial cells are characterized by a square cell shape of even size and an elongated pattern in a tubular configuration.
Epithelial mesothelioma begins in the membrane or lining cells that are found in the peritoneal (abdomen) or pleural (chest) cavities or in the pericardium (heart) or tunica vaginalis (testes). The most common occurrence of epithelial mesothelioma is the pleural malignant mesothelioma. Pleural mesothelioma refers to cancer that begins in the lining of the chest cavity.
Because epithelial mesothelioma is the most common cell type, there has been more research on treating epithelial mesothelioma than other types of mesothelioma cells. The prognosis for treating epithelial mesothelioma is slightly better than other mesothelioma cell types as a result.
Sarcomatoid mesothelioma refers to cancer cells that are structurally similar to sarcoma cells. Sarcoma cells originate in connective tissue cells like those found in bones and muscle. It is the least common form of mesothelioma and only accounts for approximately 10 to 20 percent of mesothelioma occurrences. The cells are more oval shaped, they also form in a haphazard manner. Because of their resemblance to connective tissue cancer cells, sarcomatoid mesothelioma is difficult to diagnosis. The only way is can be definitively identified is through a biopsy and pathology analysis. Even then there can be difficulties differentiating the sarcomatoid mesothelioma from other cell tumors that are pleural based and spindly.1
Unfortunately, this particular type of mesothelioma is sometimes misdiagnosed as lung cancer. It is also difficult to treat as the cancer cells are very resistant to current treatments options including radiation therapy and chemotherapy. Even surgery is less successful than it is when used as a treatment option in epithelial mesothelioma. If the cancer is advanced, treatment is often foregone.
Biphasic mesothelioma cells account for 20-35% of mesothelioma cases. Also known as mixed mesothelioma, biphasic mesothelioma includes a mix of both epithelial and sarcomatoid mesothelioma cells. These different cells may coexist in a tumor or, more commonly, present themselves separately as different areas of the same tumor. The biphasic mesothelioma cells are oval shaped and grow in a very irregular pattern.
It is often difficult to correctly diagnosis biphasic mesothelioma because the cells may be located apart from each other and a biopsy may not obtain tissue containing both cell types unless the sample is large enough.
Why Cell Type Matters with Mesothelioma
Foremost, correctly identifying cell type is important for an accurate diagnosis of mesothelioma. The cell histology will also factor in while determining the treatment for a patient. Some cells types will respond better to one form of treatment while another cell type could require a different approach. Further, new research is showing that mesothelioma cell type has a direct link to prognosis.
In the past, the prognosis of mesothelioma cancer almost solely depended on its stage. Now there is exciting research concerning the identification of markers for more accurate and earlier diagnosis and hopefully one day the development of a targeted treatment option.2 A study conducted by research teams from Memorial Sloan-Kettering Cancer Center in the United States and Kagawa University in Japan are showing that the nucleus of a cancer cell is more effective in determining prognosis than cancer stage.
During the study, the researchers examined the cancer cells of over 20 patients with epithelial pleural mesothelioma. Numerous aspects of the cells’ nuclei were analyzed including the appearance, the patterns of the DNA and proteins, additional proteins, and abnormal divisions of chromosomes. The study concluded that two aspects of the epithelial nuclei – nuclear atypia and mitotic count – were linked to the patients’ prognoses. Further, these features could also help predict when mesothelioma recurrence would happen after surgery of resectable mesothelioma. While more research is needed, this study shows that the cell types have an important role in patient prognosis and also route of treatment.
As a mesothelioma patient, it is important to be aware of your cell histology. There may be clinical trials going on which study specific mesothelioma cells. You will only be eligible for these trials if you have the mesothelioma cell type being studied in the trial. You will also only be eligible for compensation if you obtain an accurate pathological diagnosis.3
1 Lucas, D. R., Pass, H. I., Madan, S. K., Adsay, N. V., Wali, A., Tabaczka, P. and Lonardo, F. (2003), Sarcomatoid mesothelioma and its histological mimics: a comparative immunohistochemical study. Histopathology, 42: 270–279.
2 Facchetti, F., Lonardi, S, Gentili, F, Bercich, L et.al. (2007) Claudin 4 identifies a wide spectrum of epithelial neoplasms and represents a very useful marker for carcinoma versus mesothelioma diagnosis in pleural and peritoneal biopsies and effusions. Virchows Arc. v451:669-680. DOI 10.1007/s00428-007-0448-x.
3 Inai, Kouki. (2008) Pathology of mesothelioma. Environmental Health and Preventive Medicine. V13:2, 60-64.