Mesothelioma is a rare and aggressive form of cancer that affects the lining of your lungs, heart, chest wall or abdomen. The symptoms may vary depending on where it forms in your body. Some common mesothelial cells tumors are found in the air sacs called pleura which line the inside of both lungs, pericardium (a layer surrounding your heart), diaphragm and beside major blood vessels near organs such as lungs and kidneys.