Benign Mesothelioma is a form of mesothelioma which is not harmful. It is also known as Non-cancerous mesothelioma. Here is some more info about benign mesothelioma.

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Mesothelioma is a rare form of lung cancer usually associated with asbestos inhalation but not always caused this way. It is possible you are experiencing Benign Mesothelioma. Obviuosly benign means harmless but I dont know if mesothelioma is ever harmless.