thymoma

Thymoma is a tumor that arises from thymic epithelial cells in the anterior mediastinum. It is typically slow-growing and represents one of the more common thymic neoplasms found in adults. Thymomas are distinct from thymic carcinomas and other mediastinal tumors. They are often discovered incidentally or in association with autoimmune conditions, most notably myasthenia gravis.

Histologically, thymomas are classified by the World Health Organization into types A, AB, B1, B2, and B3, reflecting variations in epithelial cell morphology and lymphocyte content. Thymic carcinomas are separate entities and generally more aggressive. Thymomas commonly accompany autoimmune disorders, including myasthenia gravis and, less often, pure red cell aplasia.

Patients may be asymptomatic or present with symptoms related to a mediastinal mass or associated autoimmune disease. Imaging starts with chest CT to characterize the mass and assess invasion. MRI or PET-CT can aid staging. In cases planned for surgery, a preoperative tissue diagnosis is not always required; biopsy is used when non-surgical therapy is considered.

Staging employs Masaoka-Koga or IASLC/ITMIG TNM systems based on invasion and spread. Prognosis is generally favorable for early-stage, completely resected thymomas and worsens with invasion or metastasis. Thymic carcinomas have a poorer prognosis and different treatment considerations.

Management centers on surgical resection when feasible. Complete thymectomy or thymomectomy is the primary treatment for resectable thymomas. Adjuvant radiotherapy is considered for invasive disease. Platinum-based chemotherapy is used for unresectable, recurrent, or metastatic disease and for thymic carcinomas. Treatment of associated myasthenia gravis follows standard MG care, with thymectomy providing potential symptom relief in some patients.