Is Mesothelioma Always Malignant?

Malignant mesothelioma is a form of cancer that affects the mesothelium, which is the lining of tissue that surrounds several vital organs. The organ tissues most likely to be affected by mesothelioma generally surround the lungs, heart, and abdomen. Very rarely, the tunica vaginalis or lining surrounding the testicles can also be affected.