Malignant thymoma: current status and future directions

Malignant thymomas are rare indolent tumours of the anterior superior mediastinum. Despite a benign histologic appearance, some thymomas invade nearby structures or metastasize. Patients are commonly asymptomatic, but some may present with unusual paraneoplastic syndromes such as myasthenia gravis, pure red cell aplasia, or hypogammaglobulinemia. Since tumour biopsy may potentially disrupt the thymic capsule, it is often not performed. Patients are therefore diagnosed and staged at the time of definitive surgery. Thymomas can generally be categorized into two stages: non-invasive and invasive. Prognosis closely parallels the disease stage. Surgery is the principal treatment and is curative in early stage disease. Radiation therapy, either alone or in combination with chemotherapy, is an option for both incompletely or completely resected disease. Chemotherapy is offered to patients with locally advanced, recurrent, or metastatic thymoma, with excellent responses and prolonged survival. Multicentre co-operative group clinical trials are required to assess novel thymoma therapies to maximize patient resources in this uncommon tumour.