Pathology of thymic tumors.

As the thymus is composed of heterogeneous admixture of lymphoid and epithelial elements, tumors originating in the thymus may be of varied histologic types. Thymomas are the most common thymic tumor in adults. Thymoma classification has historically been controversial, but a system put forth by the World Health Organization (WHO) in 2004 has been generally accepted as a reproducible and clinically relevant classification. In addition to histologic subtype, tumor stage and resection status are important factors in determining outcome in thymomas. Thymic lymphomas typically occur in younger patients than thymomas. The most common thymic lymphomas are precursor T-lymphoblastic lymphoma, Hodgkin lymphoma, and primary mediastinal large B-cell lymphoma. Thorough histologic sampling and, in some cases, the appropriate use of ancillary studies such as immunohistochemistry, flow cytometry, and molecular studies, are important in proper pathologic evaluation of thymic tumors.