Physicians and researchers specializing in malignant mesothelioma have long recognized three different subtypes of pleural mesothelioma: epithelioid, sarcomatoid, and biphasic. In recent years scientists have identified a fourth, pre-invasive subtype, and in 2021 the World Health Organization (WHO) recognized “mesothelioma in situ” as an official histological subtype of the rare, asbestos-related disease.
Distinguishing Subtypes of Mesothelioma
The distinguishing features of the three previously-identified subtypes of malignant pleural mesothelioma can only be seen under a microscope, but each represents a starkly different prognosis. The majority of those diagnosed with pleural mesothelioma have the epithelioid subtype, and generally respond better to treatment and live longer than those with sarcomatoid or biphasic cell types.
The fourth, newly recognized subtype is known as mesothelioma in situ. The term describes patients who have not yet developed pleural tumors or symptoms of the rare, asbestos-related disease. They only have a thin layer of mesothelioma cells, referred to by the WHO as ‘… a pre-invasive single layer surface proliferation of neoplastic mesothelial cells’ that are usually detected when patients are being biopsied for other conditions.
New Diagnostic Category of Mesothelioma
The first identification of mesothelioma in situ came in 2019, when it appeared in a report published by Canadian researchers. Not all patients who had the cell type ended up developing mesothelioma tumors, and among those who did the process took an average of five years. That extended period of time provides physicians a significant window in which to treat patients using immunotherapy and other promising protocols.
In a report published in a recent issue of the journal Pathology, researcher Sonja Klebe of the Department of Anatomical Pathology, Flinders University and SA Pathology, Adelaide, SA, Australia discussed the newest subtype, saying, “It suggests that pre-invasive disease precedes the invasive (and essentially treatment resistant) manifestation of MM. Such a diagnosis may provide opportunities for earlier diagnosis and treatment, and ultimately, better clinical outcomes.”
If you or someone you love is at risk for or has been diagnosed with malignant pleural mesothelioma, developments in our understanding of the disease will significantly improve treatment. For more information, contact the Patient Advocates at Mesothelioma.net at 1-800-692-8608.
