- Tumors of the thymus are rare and can be treated with surgery, but it is often difficult to determine whether a thymic tumor is malignant based on biopsy alone and the long-term survival rate is less than 50 percent. Because thymic tumors are so rare, most treatment knowledge comes from a relatively small series of cases, and the choice of treatment usually depends on the hospital or clinic staff's experience and familiarity with a given chemotherapy and surgery regimen.