See below. Generally a slow growing tumor and are locally invasive. Most low grade tumors are benign and often cured with surgery alone.
Generally slow. This link may provide more information. If you have a thymoma, i encourage referral to qualified minimally invasive thoracic surgeon. Thymoma can often be removed minimally invasively with robotic or vats approach. The following links may provide more information: http://goo.Gl/mqtn1 and this one: http://goo.Gl/oetwz and this one: http://goo.Gl/yjnh5.
Slow. Slow - slow.