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How does a pathologist diagnose mesothelioma?

The most critical issue when dealing with a patient with a pleural or peritoneal tumor is to perform all the necessary tests to reach a reliable diagnosis.  Often the first suspicion comes from cytology as patients with MM may require drainage of the fluid that accumulates in the pleura or in the peritoneum.  Although cytology is useful to suggest the diagnosis of MM, it is insufficient to confirm the diagnosis as other malignancies can show identical morphology. Therefore, the current standard of treatment requires that the diagnosis is confirmed by a tissue biopsy followed by immunohistochemistry of the tumor specimen using a large panel of markers to distinguish MM from other tumors. If the resources are available, and always when immunohistochemistry is not clear-cut, EM studies should be conducted to verify the diagnosis. Too many times these procedures are by-passed and the diagnosis is rendered on insufficient information increasing the chance of errors. For example Iwatsubo et al (2001) reported that 10% of the previously diagnosed MM they studied, had in fact carcinomas and other malignancies and they suggested that the risk of misdiagnosis was higher when a patient had a documented history of asbestos exposure (Iwatsubo et al., 2001). In a large follow-up study that covered 25% of the French population, Goldberg et al (2006) reported that the initial diagnosis of MM was confirmed only in 67% of the cases, was ruled out in 13% of the cases previously diagnosed as MM, and left uncertain in the remaining cases. I have had over the years the same experience, and I found that the opposite mistake, incorrect diagnosis of a carcinoma or a sarcoma in a patient with MM, is also relatively common. Thus, too many patients continue to be misdiagnosed and consequently do not receive proper treatment for their pleural or peritoneal tumors. My strong advice to patients is to always ask for a second opinion: this is a major diagnosis, too many times is wrong, once is wrong it is very unlikely that will be changed because physicians will be biased by the previous diagnosis and will not know that probably was made on insufficient material or information.  The results can be devastating, I have seen horrible stories, for example US patients who had no cancer at all, who had a chronic benign pleuritis who were sent to hospice care and who eventually contacted me years later because they wanted to know why they were not dying: well they had no cancer in the first place!  Patients can contact MARF that can certainly provide them with a list of the centers that have experience with MM and that should have pathologist that can critically review the diagnosis. 

--Michele Carbone, MD, PhD, University of Hawaii

Goldberg M, Imbernon E, Rolland P, Ilg AGS, de Quillacq A, Frenay C, Chamming’s S, Arveux P, Boutin C, Pairon JC, Astoul P, Galateau-Salle` F, Brochard P.  2006.  The French National Mesothelioma Surveillance Program.  Occup Env Med 63:390-395.

lwatsubo Y, Pairon JC, Boutin C, Menard 0,Massin N, Caillaud D, Orlowski E, GalateauSalle F, Bignon J, Brochard P. Pleural mesothelioma: dose-response relation at low levels of asbestos exposure in a French populationbased case-control study. Am J Epidemiol 148:133-142 (1998).


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