Metaplastic thymoma: A rare and indolent subtype.

Though thymomas are the commonest neoplasms of the anterior mediastinum, metaplastic thymoma is an extremely rare subtype, with only a few reported cases. It was included in the 2004 WHO classification of thymic epithelial tumors and exhibits a biphasic morphology distinct from the conventional thymomas. It has a benign clinical course with extremely rare cases showing recurrence and malignant transformation. However, metaplastic thymoma needs to be histologically distinguished from other more aggressive mediastinal neoplasms displaying biphasic patterns. Here we report a case of an incidentally detected large mediastinal mass with features of metaplastic thymoma.