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New Mesothelioma Grading System: A Better Path to Prognosis?

mesothelioma grading systemA team of Australian researchers have developed a new mesothelioma grading system they believe is a more accurate method for predicting outcomes.

The system assigns weighted scores based on things like mesothelioma subtype, the shape of the nuclei, BAP1 loss and other parameters. A higher score suggests the patient’s mesothelioma case may be more challenging to treat. Tests of the system in more than 350 patients show that it is highly accurate. 

The team lays out their new mesothelioma grading system in a recent issue of the American Journal of Surgical Pathology. In the article, they make the case for why this new prognostic tool could be a helpful supplement to the current, more widely-used WHO system. 

The Importance of Categorizing Mesothelioma

Malignant mesothelioma is a virulent cancer that affects the membranes around internal organs. Most people who get this cancer have a history of exposure to asbestos. Pleural mesothelioma, which is a form of lung cancer, is the most common type. 

Every year, more than 2,500 Americans and tens of thousands around the world contract this deadly cancer. While treatments are improving, there is still no cure. 

A mesothelioma grading system is not just a way to predict treatment outcomes. Prognostic tools also help doctors and patients plan treatment and make decisions. 

Pleural mesothelioma grows and spreads quickly. But there are many factors that impact that growth. In addition, certain mesothelioma subtypes are more responsive to standard treatments than others. A mesothelioma grading system gives doctors a straightforward way to understand what they are dealing with so they can choose the best approach. 

Understanding the Mesothelioma Weighted Grading Scheme

Mesothelioma is a worldwide problem. Even though the numbers of mesothelioma cases have started to dwindle in the US in recent years, tens of thousands of people are still impacted in many other countries. 

The new mesothelioma grading system could impact how these patients are treated. It assigns more “weight” to factors that negatively impact survival. The system assigns a score of 1 to 10 based on

  • Age (under 74 versus over 74)
  • Histologic type (epithelioid, biphasic, sarcomatoid)
  • Necrosis (cell death – absent or present)
  • Mitotic count (how many cells are undergoing mitosis/cell division)
  • How many of the cells’ nuclei are atypical (mild, moderate, or severe)
  • BAP1 protein status (lost or retained)

A score of 0 to 3 is low grade, 4 to 6 is intermediate grade, and 7 to 10 is high grade mesothelioma. 

“In 369 consecutive [pleural mesothelioma cases], median survival was 17.1, 10.1, and 4.1 months for low, intermediate, and high grades,” say the creators of the Mesothelioma Weighted Grading Scheme (MWGS). “A progressive increase in score correlated with worsening overall survival.”

How the New Mesothelioma Grading System Compares

The MWGS is not the only system for assessing the severity of mesothelioma tumors. The World Health Organization has a two-tiered mesothelioma grading system, now in its fifth edition. But the Australian researchers who developed the proposed new system say the WHO approach is not as effective at accurately predicting mesothelioma survival.

“The WHO system predicted median survival in epithelioid and biphasic but not sarcomatoid DPM (diffuse pleural mesothelioma),” states the report. “Interestingly, the WHO grading system was prognostic in cases with BAP1 loss, but not retained BAP1 expression.”

The team concludes that, while the WHO mesothelioma grading system has merit for some patients, the MWGS can be used to assess mesothelioma risk for all mesothelioma cases, regardless of histologic subtype or BAP1 status. 


Fuchs, T, et al, “A Critical Assessment of Current Grading Schemes for Diffuse Pleural Mesothelioma With a Proposal for a Novel Mesothelioma Weighted Grading Scheme (MWGS)”, December 15, 2021, American Journal of Surgical Pathology, Online ahead of print, https://journals.lww.com/ajsp/Abstract/9000/A_Critical_Assessment_of_Current_Grading_Schemes.97085.aspx

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