Introduction to Malignant Pleural Mesothelioma

H. Jack West, MD, Founder, President and CEO

We haven't covered this on OncTalk yet, but it's a real shortcoming that I haven't discussed malignant pleural mesothelioma (MPM). Although it's not exactly lung cancer, it's another chest cancer that is often managed by thoracic oncology specialists like myself, and the only reason I haven't introduced it until now is that it's such an unusual cancer, accounting for just 2000-3000 cases each year in the US. But it's infrequency means that it doesn't get studied or discussed, so the people with MPM have far less information and support available for them (the one clear exception, aside from lawyers who are avidly interested in working with MPM patients, is MARF, the Mesothelioma Applied Research Foundation, which is a phenomenal central resource for the small but mightly mesothelioma community). By contrast, lung cancer is unfortunately a very common cancer, but at least being common means that your get a reasonable amount of attention and research dedicated to the problem.

MPM is a cancer of the pleural lining around the lung, not the cells of the lung itself. Normally a thin onion-skin-like layer, this layer thickens to something more like an orange rind but often thicker and tougher often adhering to nearby structures like the chest wall, heart, and major blood vessels. It looks like this on CT, with the thick MPM tumor on the left side of the chest, which is the right side of the CT images here:

MPM on CT (Click to enlarge)

People with MPM have been known for the association of this disease with asbestos exposure, which has led to the companies involved with products that entailed asbestos exposure being sued on behalf of attorneys seeking expenses and damages on behalf of the patients and their families. A majority, but certainly not all, of the patients with MPM have identified exposure to asbestos, including working as a pipefitter, naval yard worker, railroad brake man, certain aspects of construction, and others. This is typically a disease of men, about 4-5 times as many men as women, believed to be because of the occupational exposure of men to asbestos. Some of the women who have developed MPM have been the wives or daughters of men who had significant asbestos exposure, as these women were indirectly exposed by tending to the laundry or caring for the man who had the direct exposure.

There are certainly other potential contributing factors, including an ongoing debate about whether simian virus-40 (SV40) is a key component in MPM (one reference here). Tobacco use is also felt to potentially have a synergistic role with asbestos in developing mesothelioma.

The most common symptoms of MPM are non-exertional chest pain and shortness of breath, and presenting with a large pleural effusion is particularly common. This effusion is typically drained, and the fluid is often sent for cytology, the microscopic evaluation of cells in the fluid. It is debated whether a pathologist can really make a conclusive diagnosis from cells in fluid; some pathologists say that the diagnosis can really only be made from a biopsy of pleural tumor tissue, which is often obtained by a thoracoscopy. This is a minimally invasive chest surgery that involves making a very small invision to put a "thoracoscope", another basic tube with a light source, camera, and biopsy tools, inside the long, narrow tube that is so similar to the EGD scope used to diagnose gastric or esophageal problems, or a bronchoscopr looking at the bronchial tree, or a colonoscope. Sometimes surgeons will do a thoracoscopy to perform a pleurodesis to control recurrent effusions and at the same time have a good opportunity to look inside the chest to obtain tissue samples as needed to make a definitive diagnosis.

MPM is typically a disease of advanced age, as there is usually a 20-30 year interval between asbestos exposure and development of the disease. Because of this, the disease is typically seen in men in their late 60s or well into their 70s, and this factor has limited the ability to pursue some very aggressive treatment approaches like surgery, which has often involved a very challenging approach called an extrapleural pneumonectomy -- taking out the entire lung along with the pleural lining/tumor around it. It makes the more typical lung surgery of a lobectomy seem like a cakewalk. These procedures, and indeed much of the specialized aggressive treatment for MPM, has been concentrated at just a handful of specialty centers in the US and somewhat outside of the US.

But since most patients with MPM present with more advanced disease than even very well trained thoracic surgeons can manage, and also because many patients are older and/or sicker from unrelated medical problems than a good candidate for such aggressive treatment would be, the main treatment for MPM has been chemotherapy. Until about 2002, the more optimistic of us tried chemo options that had no really established role, and many other physicians felt that there was nothing to offer but comfort care. Fortunately, the last five years have brought renewed study and interest, and most importantly new and somewhat effective treatment options, so I'll cover the highlights of that work very soon.


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