Histochemical and immunohistochemical evidence of glandular differentiation in thymic carcinoma

Eighteen cases of primary thymic carcinoma were reviewed from the viewpoint of glandular differentiation. Squamous differentiation was evident in 14 cases (83%). Immunohistochemical study revealed secretory component (SC)-positive carcinoma cells in 12 cases (67%), most of which were also associated with squamous differentiation. Three of these 12 cases contained areas with a definite glandular or microcystic structure with occasional epithelial mucin, and were diagnosed as adenosquamous carcinoma. Review of patients' medical records revealed that thymic carcinomas with a glandular element were more often resectable at surgery, and had a much better prognosis than those without a glandular element. However, further study on larger number of cases is necessary to confirm this relationship. Because SC-positive epithelial cells do exist in the non-neoplastic thymus, the presence of a glandular component suggests another direction of morphological and/or functional differentiation of thymic carcinoma cells in addition to the well-known squamous differentiation.