Mesothelioma | Mesothelioma Law Firm | mesothelioma survival rates | mesothelioma suit br what is mesothelioma br Mesothelioma is a type of cancer that develops from the thin layer of tissue that covers many of the internal organs (known as the mesothelioma). The most common area affected is the lining of the lungs and chest wall.Less commonly the lining of the abdomen and rarely the sac surrounding the heart, or the sac surrounding the testis may be affected.