Mesothelioma Science

Malignant mesothelioma typically presents as a diffuse disorder, with a large number of tumors spread throughout an entire tissue area. Localized presentations, where histological analysis clearly establishes a diagnosis of malignant mesothelioma but whose behavior is characterized by a single mass without evidence of diffuse spread or distant metastases, are exceedingly rare tumors. In fact, the literature only describes forty-five such cases. Due to its rarity, little is known about this form of mesothelioma.

The first descriptions of localized mesothelioma appeared in the early 1990s and described a cohort of six patients. After this initial report, additional studies and anecdotal reports began to appear, but these were few and relatively far between. In 2005, researchers presented the largest current analysis of localized mesothelioma, which described twenty-three new cases and summarized the literature on the previously reported cases. Of the forty-five known cases, thirty-nine presented with a localized pleural tumor. Two presented with a localized peritoneal tumor and two others presented with a localized pericardial tumor.

With so few cases to study, the Japanese researchers were not able to make definitive conclusions on the etiology and underlying development of the disease, but they were able to use their case report to make some general statements on localized mesothelioma.
Case Study

The researchers describe a 54 year-old man suffering from chest discomfort and heart palpitations. An x-ray revealed an abnormal shadow in the area of his chest associated with the discomfort and CT showed pleural thickening. He was given a diagnosis of a benign pleural tumor and then told to return in a few months for a follow-up. After six months the tumor had grown only slightly, but a CT taken fourteen months later showed significant increase in tumor size and some evidence of chest-wall invasion. A needle biopsy returned results positive for malignant mesothelioma, but physical examination revealed a localized neoplasm without tissue diffusion or distant metastases.

Surgery was then scheduled to remove the growing mass. Doctors identified and removed a single tumor approximately 5cm in size. The tumor had invaded the middle lobe of the lung, but no farther. Histopathology of the tumor itself confirmed malignant mesothelioma, biphasic type. There was neither diffuse spread of the tumor throughout the pleura, nor were any pleural effusions discovered—a clear indication of the behavioral differences between localized and diffuse mesothelioma.

The surgery was declared a complete success when all surgical margins were negative for malignant tissue. The doctors report the man’s prognosis as excellent. Two years after his surgery he is free of the cancer and it shows no signs of returning.
Conclusion

Localized malignant mesothelioma is a very rare subclass of mesothelioma. Normally characterized by gross tissue involvement and general resistance to treatment, malignant mesothelioma remains among the most difficult of all cancers to manage effectively. Prognosis is generally poor and life expectancy is often reduced.

The localized variant of the disease shows none of these characteristics. Histologically the disease is mesothelioma, but its behavior is quite different. Instead of diffuse spread, this version of the disease presents as a single mass with clear boundaries and a seemingly non-aggressive development pattern. As in the case of the man covered here, the tumor appears to be rather slow-growing (there was a period of 16 months between initial x-ray and surgery) and quite amenable to treatment. While a few of the cases in the literature report a metastatic potential and some recurrence after surgery, most do not, so the prognosis for a person with localized mesothelioma seems to much better than a person with the more commonly-seen diffuse disease.