The thymus gland is needed as a child,& is located over the heart, as you mature your body doesn't need it anymore. But grows & spreads. People with MG are predisposed to cancer in this gland, & they don't really understand medically, but when removed, MG symptoms improve at different levels, for different people. So it is used for a treatment for MG, & gets rid of cancer, or takes that possiblity away ! There is more detail about this on the web, this is just my understanding, when I had it done.
Also welcome, I hope I have helped you, there is a lot of people on this forum that have had this done.
Mary