CD5 IMMUNOREACTIVITY OF EPITHELIAL-CELLS IN THYMIC CARCINOMA AND CASTLE USING PARAFFIN-EMBEDDED TISSUE

Because the histologic features may resemble those of other mediastina l malignancies, thymic carcinoma can be difficult to diagnose, particu larly if the primary site is uncertain. In an effort to facilitate thi s diagnosis, the authors have evaluated the use of immunohistochemistr y with an antibody to CD5 (NCL-CD5). Nine thymic carcinomas, 15 thymom as, 8 lymphomas, 10 poorly differentiated lung carcinomas, 10 breast c arcinomas, 1 mediastinal seminoma, and 1 thyroid carcinoma showing thy mus-like differentiation (CASTLE) were studied. Four of 9 poorly diffe rentiated carcinomas of the thymus were CD5 positive. The one CASTLE w as CD5 positive. All other tumors were negative. CD5-positive lymphocy tes were internal controls in every case. CD5 labels some thymic carci nomas in paraffin-embedded tissue, whereas other tumors studied were n egative, CD5 immunoreactivity of CASTLE appears to support thymic deri vation of this tumor.