Thymic carcinoma with focal neuroblastoma differentiation.

A small, incidentally found, thymic carcinoma (malignant thymoma) showed an extraordinary mixed-cell composition. The tumor was predominantly made up of poorly differentiated cells with light-microscopic, ultrastructural, and immunohistochemical features of thymic epithelium. However, small distinct groups of cells displaying features of neuroblastoma were scattered throughout the tumor. This unique case further illustrates the multiple capabilities of differentiation of thymic tumors.