Thymomas
Thymomas are rare tumors that form on the thymus, a small organ located in the upper chest, and are classified as epithelial tumors. They are most commonly associated with myasthenia gravis, with a significant proportion of thymoma patients (30% to 80%) also suffering from this autoimmune disorder. Thymomas are categorized by the World Health Organization into various types based on their microscopic appearance, ranging from Type A with spindle-shaped cells to Type C, which involves invasive thymic carcinomas.
Although thymomas generally do not present symptoms, they can lead to respiratory issues, chest pain, and other complications when they compress nearby structures. Diagnosis often occurs incidentally during examinations for other conditions, with definitive diagnosis typically achieved through surgical intervention. Treatment primarily involves surgical removal of the thymus, known as thymectomy, and may include chemotherapy or radiation therapy, especially in advanced stages.
The prognosis for thymoma patients is generally favorable, particularly for early-stage cases, with five-year survival rates as high as 95% for localized tumors. However, survival rates for thymic carcinoma are lower, with 30% to 50% of patients surviving at least five years post-diagnosis. Overall, while there is no known prevention, advancements in treatment options are improving outcomes for those affected.
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Subject Terms
Thymomas
ALSO KNOWN AS: Epithelial tumors of the thymus, thymic tumors
RELATED CONDITIONS: Thymic cancer, carcinoid tumors, germ-cell tumors, lymphomas
DEFINITION: Thymomas are abnormal tissue masses on the outside of the thymus, a small organ in the upper chest.
Risk factors:Myasthenia gravis is the primary disorder associated with thymomas, occurring in about 30 to 50 percent of patients with thymomas, according to the National Institutes of Health, although this number may be as high as 80 percent. Red cell aplasia and hypogammaglobulinema are tumor-related conditions that may occur with thymomas. Autoimmune diseases increase the risk.
Etiology and the disease process: The World Health Organization’s letter grade system identifies thymomas based on their microscopic appearance:
- Type A: Spindle-shaped endothelial cells, few lymphocytes
- Type AB: Features of type A plus lymphocytes
- Types B1 and B2: Numerous lymphocytes, thymus cells normal (B1) or abnormal (B2)
- Type B3: Few lymphocytes, normal thymus epithelial cells
- Type C (thymic carcinomas): Mature lymphocytes mixed with plasma cells, invasion of surrounding tissues
Incidence: Thymomas and thymic cancers are rare. Thymomas occur at a rate of 0.13 to 0.32 cases per 100,000 people. Thymic carcinomas may be even rarer. The incidence of nonmalignant thymomas is unknown. Thymomas usually affect people aged forty to sixty years.
Symptoms: Symptoms are often related to other coexisting conditions. Thymomas may cause shortness of breath, coughing, and angina when there is added pressure on the nearby airways or blood vessels. Chest pain, swelling, muscle weakness, hoarse voice, anemia, and changes in appetite or weight loss are additional symptoms. Most patients do not experience symptoms, but the thymoma is found during examination for another medical condition.
Screening and diagnosis: A needle biopsy may be performed, but thymomas are usually diagnosed, staged, and treated during surgery.
- Stage I: Noninvasive, within thymus boundary
- Stage II: Spread beyond the thymus, affecting fatty tissue or mediastinum
- Stage III: Extending to the pleura, pericardium, lungs, nerves, or superior vena cava
- Stage IVA: Spread throughout the pleura and pericardium
- Stage IVB: Spread to distant organs
Treatment and therapy: Surgical removal of the thymus (thymectomy) and some of the surrounding tissue is recommended. Removal of nearby structures affected by the malignancy may be necessary for Stage III or IV thymomas. Chemotherapy, radiation therapy, or both may decrease the size of the tumor before surgery and may be given after surgery. New drugs have improved thymoma treatment as well. PT-112, along with multikinase inhibitors such as lenvatinib and regorafenib kill cancer cells and boost the immune system. Cytokine-based treatments, a novel form of immunotherapy, were also being investigated.
Prognosis, prevention, and outcomes: The prognosis depends on the stage of the disease, with the highest survival rates for patients with Stage I and II thymomas that undergo thymectomy. According to the National Cancer Institute, in 2024, between 30 and 50 percent of patients with thymic carcinoma survive for at least five years. The five-year survival rate for patients who have tumors localized to the thymus, however, can be 95 percent. There is no known prevention for thymomas.
Bibliography
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