Current Staging For Thymomas


Stage I- tumor with intact capsule; Stage II- transcapsular extension into the mediastinal fat (IIa- microscopic invasion through the capsule and IIb- macroscopic invasion into surrounding fat); Stage III- invasion of the adjacent organs - focal pleural or pericardial, mediastinal structures (great vessels, heart), or lung; Stage IVa- pleural or pericardial dissemination; and Stage IVb- Lymphatic or hematogenous metastases [21]. Stage I lesions are treated with surgical resection alone, while stage II lesions are treated with surgery and post op XRT if the resection is incomplete [21]. For stage III and IVa lesions, patients receive adjuvant chemotherapy followed by surgery and XRT if required [21]. Stage IVb lesions are treated with palliative chemotherapy [21].
Prognosis for a non-invasive thymoma is very good with only a 2% recurrence rate for encapsulated lesions. Invasive lesions have a 50-78% 5 year survival [2]. The reported average time to recurrence of a completely resected thymoma is approximately 5 years- hence, long term followup of these patients is required [21].Excision of the lesion generally results in improvement in the clinical status of myasthenia patients- often resulting in complete remission. 
On histologic analysis a thymoma consists of a mixture of thymic epithelial cells and lymphocytes. The epithelial cells may be spindle-shaped and if more than two thirds of the epithelial cells have this appearance, the thymoma is classified pathologically as a 'spindle cell tumor.' Purely lymphocytic and spindle cell thymomas have been suggested to be less aggressive than epithelial and mixed lymphocytic/epithelial thymomas [3].

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