CD5 EXPRESSION IN THYMIC CARCINOMA

To determine the differences between the cellular characteristics of t hymic carcinoma and thymoma, immunohistochemical analysis with lymphoc yte markers (CD1a, 3, 4, 5, 8, 10, 20, 21, 25, 30, 57, and 72) was per formed on 23 thymic epithelial tumors other than lymphocytic thymoma: overt thymic carcinoma (OC, n = 7), atypical thymoma (n = 5), and typi cal thymoma (epithelial or mixed thymoma, n = 11). Among the surface a nti,pens examined, CD5, a type of receptor molecule that signals cell growth in T cells, was expressed in neoplastic epithelial cells of the thymus, in OC (seven of seven) and atypical thymoma (two of five), bu t not in typical thymoma. Double labeling immunofluorescence demonstra ted expression of CD5 in cytokeratin-positive cells. The CD5 molecule extracted from an OC tumor showed the same molecular size as that in t he spleen, but CD72, a ligand of CD5 on the surface of B cells, was no t found in the epithelial cells of OC or atypical thymoma. Expression of CD5 was not observed in carcinomas of other organs, such as lung (n = 15), breast (n = 4), esophagus (n = 6), stomach (n = 6), colon (n = 3), and uterine cervix (n = 3) CD5 is closely related to morphologica l changes in thymic epithelial tumors and may play a rob in the evolut ion of Oc through receptor-ligand interaction.