Mesothelioma Differential Diagnoses, Mesothelial hyperplasia

Hollevoet et al found that megakaryocyte potentiating factor (MPF) can be used as a serum biomarker of malignant mesothelioma. MPF originates from the same precursor protein as soluble mesothelin (SM), which is currently the reference serum biomarker for malignant mesothelioma. At 95% specificity, SM had a sensitivity of 64% (cutoff = 2.00 nmol/L) and MPF had a sensitivity of 68% (cutoff = 12.38 ng/mL). Combining both markers did not improve the diagnostic performance.5

Pleural fluid findings in patients with mesothelioma are typically not diagnostic. The specific gravity of the pleural fluid is nondiagnostic.

Typically, the pleural fluid has less than 1000 leukocytes per microliter, few erythrocytes, elevated protein levels, and normal lactate dehydrogenase levels.

Results of cytologic examination are occasionally positive for malignant mesothelial cells; however, most often the pleural fluid cytology results are not diagnostic.6

Diagnosis is made based on the following:

More than 90% of patients present with pleural effusion that decreases after thoracentesis. Cytologic examination findings are diagnostic in only 32% of patients and are suggestive in 56% of patients. Thoracoscopically guided biopsy should be performed if mesothelioma is suggested, and results are diagnostic in 98% of cases.

Careful scrutiny of routinely stained biopsy preparations is the most valuable diagnostic tool for making a diagnosis. A battery of commercial immunohistochemistry stains (eg, for cytokeratins, vimentin, human milk fat globulin 2, anti-Leu M1, BerEP4, and carcinoembryonic antigen) can be used

Diagnostic features distinguishing malignant mesothelioma from carcinogenic include negative test results for periodic acid-Schiff stain, mucicarmine stain, carcinoembryonic antigen, and Leu M1 and positive test results for calretinin, vimentin, and cytokeratin. Electron microscopy reveals that cells have long microvilli, in contrast to adenocarcinomas, which have short microvilli.

One of the new most intriguing markers is serum mesothelin-related protein (SMRP) measured in fluid or serum. The circulating SMRP level was reported to be elevated in 84% of patients with malignant mesothelioma and in 2% of patients with lung cancer.