* Thymomas represent 20 percent of all mediastinal neoplasms in adults; they are most common anterior mediastinal primary neoplasm in adults but are rarely seen in children. Thymomas are slow growing, but are still considered malignant neoplasms because of their invasive potential.
* Epidemiology: Commonly presents between the ages of 30 and 50.
* Clinical findings - Approximately 50 percent of patients with thymoma are asymptomatic at the time of diagnosis and are discovered incidentally, usually because a chest film or transthoracic echocardiogram obtained for an unrelated purpose is suggestive of an anterior mediastinal mass. 35% of patients present with myasthenia gravis or other tumor related syndromes (see below). 15% with substernal pain, dyspnea, or cough.
* Paraneoplastic syndromes - Myasthnia Gravis, pure red cell aplasia, and hypogammaglbulinemia are the three most common paraneoplastic syndromes associated with thymomas. 30-50% of patients with thymomas have MG. Patients with MG and thymomas usually present with less advanced thymomas than those without MG, as the presence of neuromuscular symptoms favors earlier tumor detection. Pure red cell aplasia occurs in 5-15% of thymoma patients. Red cell aplasia in thymoma patients is thought to be caused by antibodies to erythroid progenitors. Both MG and pure red cell aplasia can sometimes be treated with a thymectomy. This is not the case with an associated hypogammaglobulinemia, which is a rare thymoma paraneoplastic syndromes. There are also multiple case reports of patients who present with lichen planus and thymomas.
* Differential diagnosis - Thymoma, lymphoma, germ cell tumor (teratoma, seminomas), mediastinal cysts (pericardial cysts, enterogenous cysts, thymic cysts), thyroid tissue, parathyroid tissue.
* Diagnosis - CT scan or MRI can demonstrate a mass in the anterior mediastinum. The presence of myasthemia gravis or other parathymic syndromes is highly suggestive of thymoma. Tissue biopsies stain positive for cytokeratin, a protein commonly found in the epithelial cell thymomas. Immunostaining of the epithelial cells helps distinguish thymomas from lymphomas or sarcomas. The definitive diagnosis can be made only after surgical excision.
* Staging - Staging is done at the time of surgery. Stage I means a fully encapsulated mass without local invasion into the pericardium or pleura. Stage II disease has local invasion that is fully removed by surgery. Stage III disease is sub-total resection of locally invasive disease. Stage IV represents metastatic disease.
* Treatment - Surgical removal is the standard treatment. Radiation is added for Stage III disease and radation and a cisplatin-based chemotherapy is used for stage IV disease. In addition, clinicians must be aware that patients with thymoma are at increased risk of developing B-cell non-Hodgkin's lymphoma, colon cancer, and soft tissue sarcomas.
* Prognosis. The most important prognositic indicator is the presence of invasion. The 5-year survival rate with invasion is 50% versus a five year survival of rate 75% without invasion.