Incidence and risk factors
Thymoma and thymic carcinomas are very rare in children.[66,67,68] In the Tumori Rari in Età Pediatrica registry, only eight cases were identified over a 9-year period. A review of 73 cases of anterior mediastinal tumors using the SEER Registry of the National Cancer Institute identified thymic epithelial tumors as having the worst survival rate at 10 years from diagnosis; better survival rates occurred in patients with lymphomas and germ cell tumors.
Various diseases and syndromes are associated with thymoma, including myasthenia gravis, polymyositis, systemic lupus erythematosus, rheumatoid arthritis, thyroiditis, Isaacs syndrome or neuromyotonia (continuous muscle stiffness resulting from persistent muscle activity as a consequence of antibodies against voltage-gated potassium channels), and pure red-cell aplasia.[71,72] Endocrine (hormonal) disorders including hyperthyroidism, Addison disease, and panhypopituitarism can also be associated with a diagnosis of thymoma.
These neoplasms are usually located in the anterior mediastinum and are usually discovered during a routine chest x-ray. Symptoms can include cough, difficulty with swallowing, tightness of the chest, chest pain, and shortness of breath, although nonspecific symptoms may occur. These tumors generally are slow growing but are potentially invasive, with metastases to distant organs or lymph nodes. Staging is related to invasiveness.
Surgery is performed with the goal of a complete resection and is the mainstay of therapy.
Radiation therapy is used in patients with invasive thymoma or thymic carcinoma.
Chemotherapy is usually reserved for patients with advanced-stage disease who have not responded to radiation therapy or corticosteroids. Agents that have been effective include doxorubicin, cyclophosphamide, etoposide, cisplatin, ifosfamide, and vincristine.[65,69,73,75,76,77] Responses to regimens containing combinations of some of these agents have ranged from 26% to 100% and survival rates have been as high as 50%.[77,78] Response rates are lower for patients with thymic carcinoma, but 2-year survival rates have been reported to be as high as 50%.
Sunitinib has yielded clinical responses in four adult patients with thymic carcinoma.