Open Biopsy Better for Diagnosing Mesothelioma Subtype

Open surgical biopsy – called thoracotomy – appears to be the best way to get an accurate diagnosis of mesothelioma subtype.

Mesothelioma is a fast-growing malignancy caused by asbestos exposure.  Epithelial mesothelioma is the most common subtype, followed by sarcomatoid and biphasic.  Determining which subtype a patient has is an important prognostic indicator and can help guide doctors in making treatment decisions. But mesothelioma itself is notoriously difficult to diagnose, and determining subtype can be equally tricky.

To help determine the most accurate diagnostic method, a group of Australian scientists evaluated the records of 83 patients who underwent a surgical procedure called extrapleural pneumonectomy (EPP) for mesothelioma between 1994 and 2009. A panel of pathologists reviewed the specimens collected during EPP and compared their subtypes with each patient’s initial subtype diagnosis.

Prior to their surgeries, the patients had undergone different methods to try to determine which mesothelioma subtype they had:  81% of patients underwent thoracoscopy, a minimally invasive procedure that uses a special type of endoscope for visualization; 11% had biopsies done with the guidance of computed tomography (CT); 7% had the open thoracotomy procedure and 1% had another type of diagnostic procedure.

The researchers found that, overall, one in five patients were given an inaccurate diagnosis of their mesothelioma subtype.  Of the different methods used, biopsy by thoracotomy achieved accurate diagnoses in 83% of cases, compared with thoracoscopy (74%) and computed tomography-guided procedure (44%).

The epithelial subtype was diagnosed correctly in 82% of cases, but the 19 patients with the biphasic type were only diagnosed correctly 26% of the time. There were no sarcomatoid subtypes found in the study.

Because it is an open procedure, thoracotomy makes it easier for surgeons to collect a larger sample of malignant mesothelioma cells for testing. However, because it involves a large incision into the chest, it also carries a greater risk of potential complications than other diagnostic methods.

Summarizing their findings in the latest issue of the Journal of Thoracic Oncology, the research team writes, “The determination of histological subtype from a diagnostic biopsy is difficult due to sampling error, but an adequate specimen obtained from surgical biopsy increases the accuracy of subtype classification compared with radiological-guided biopsies.”

Sources:

Kao, SC et al, “Accuracy of Diagnostic Biopsy for the Histological Subtype of Malignant Pleural Mesothelioma”, January 24, 2011, Journal of Thoracic Oncology (Epub ahead of print).