Differential diagnosis of undifferentiated malignant tumors with monoclonal antibody T29/33.

An immunoperoxidase method for distinguishing lymphomas from nonlymphoid neoplasms with monoclonal antibody T29/33 is described. This antibody recognizes a 200,000-dalton pan-hematopoietic glycoprotein antigen. Staining in nearly 200 hematopoietic tumors was positive for T29/33, although three of six plasmacytomas were negative for this antibody. Five undifferentiated tumors that were proved to be lymphomas by subsequent electron microscopic and immunohistologic studies were positive for T29/33. Conversely, 11 of 12 undifferentiated tumors with ultrastructural and clinical features of carcinoma or sarcoma were T29/33-negative. The only exception was one sarcoma that was T29/33-positive. Thus, monoclonal antibody T29/33 is a valuable tool for characterizing neoplasms that cannot be diagnosed by histopathologic examination alone.