Mesothelioma Subtypes Often Misclassified by Biopsy

Pleural biopsy is not perfect when it comes to telling the difference between the three mesothelioma subtypes. But misclassification could lead to shorter survival. 

That is the conclusion reached by top mesothelioma researchers in Brescia, Italy. 

They compared autopsy records from 134 Italian mesothelioma patients. The patients were either shipyard workers or their spouses. The researchers found that the mesothelioma subtypes identified from biopsy tissue were incorrect a large percent of the time.

Misclassification matters because it impacts which mesothelioma treatments doctors choose. 

The Three Mesothelioma Subtypes

Pleural mesothelioma is an aggressive malignancy on the lung lining. It is caused by exposure to asbestos. Mesothelioma cells fall into three mesothelioma subtypes based on certain cellular characteristics. Pleural mesothelioma is notoriously difficult to treat with standard therapies. Getting the subtype right is critical for choosing the most effective treatment.

Epithelioid mesothelioma is the most common of the three mesothelioma subtypes. About half of pleural mesothelioma patients have this type. This subtype has the best response to surgery. People with epithelioid mesothelioma tend to have the best prognosis.  

About 20 percent of mesothelioma patients have sarcomatoid mesothelioma. Sarcomatoid cells are more spindle-shaped than epithelioid cells. Sarcomatoid mesothelioma is the hardest of the three mesothelioma subtypes to treat. 

Thirty percent of mesothelioma patients have both epithelioid and sarcomatoid cells in their tumors. This is biphasic mesothelioma. Like sarcomatoid, it is very hard to treat. People with sarcomatoid or biphasic mesothelioma are not good candidates for surgery. 

Pleural Biopsies Do Not Tell The Whole Story

The goal of the new Italian study was to test the accuracy of diagnoses made from pleural biopsy. Surgeons collected cells using either video-assisted thoracoscopic surgery (VATS) or surgery. They made a diagnosis and planned treatment based on their conclusions.

Those conclusions were checked against necropsy data collected after each patient died. 

Necrosy showed a breakdown of the three mesothelioma subtypes as follows: 62 epithelioid, 51 biphasic, and 21 sarcomatoid. Three quarters of the biphasic cases  had been classified as epithelioid when the patients were alive. 

The researchers found that cells obtained during either VATS or open surgery were good for correctly identifying epithelioid mesothelioma. But they were not as good at diagnosing the other two mesothelioma subtypes. 

“We observed a substantial degree of misclassification between epithelioid and biphasic MPM for pleural biopsies performed during VATS,” writes researcher Pietro Gino Barbieri in the Italian journal Tumori. “We also observed substantial misclassification of biospecimens collected during MPM surgery.”

Previous studies show that surgery can be a good treatment for epithelioid mesothelioma. But surgery is not recommended for patients with other mesothelioma subtypes.

The research team concludes that “caution should be taken” in using VATS-obtained data to choose patients for mesothelioma surgery.

Source:

Barbieri, PG, et al, “Accuracy of pleural biopsy for the diagnosis of histologic subtype of malignant pleural mesothelioma: Necropsy-based study of 134 cases”, March 15, 2021, Tumori, Online ahead of print, https://journals.sagepub.com/doi/10.1177/0300891620988354