Thymoma : Morphology

Thymomas have lobulated architecture with fibrous bands separating individual lobules as seen in this low power view. Some lobules may have angulated contours. The lobules are composed of neoplastic epithelial cells and non-neoplastic lymphocytes in varying proportions. The lymphocytes of thymoma are of T-cell derivation and have the phenotype of immature thymocytes, including positivity for TdT, CD99, and CD1a.