[Diagnosis of undifferentiated tumors by means of monoclonal antibodies on paraffin sections].

The diagnostic value of 3 monoclonal antibodies applied on to routinely processed surgical biopsies was assessed. These antibodies were directed against keratin polypeptide (KL1), epithelial membrane antigen (DAKO-EMA) and leucocyte common antigen (DAKO-LC). First, using a three-step immunoperoxidase procedure, we determined the phenotype of well differentiated carcinomas (21 cases), non-Hodgkin's malignant lymphomas (44 cases), malignant histiocytoses (3 cases), melanomas (5 cases), sarcomas (6 cases) and miscellaneous tumors (16 cases). Nineteen out of the 21 carcinomas reacted with KL1 and DAKO-EMA antibodies but not with DAKO-LC. Forty out of the 44 non-Hodgkin's malignant lymphomas reacted with DAKO-LC. All these tumors were negative with KL1 antibodies but three of them, as well as 3 cases of malignant histiocytosis, expressed the epithelial membrane antigen. The value of these 3 antibodies was then assessed in the differential diagnosis of 30 undifferentiated tumors. A definite diagnosis was made in 28 cases: there were 11 undifferentiated carcinomas and 11 large cell malignant lymphomas. The phenotype of 6 tumors was highly suggestive of malignant histiocytosis, the peculiarity of which is to express both leucocyte common (DAKO-LC+) and epithelial membrane antigens (DAKO-EMA+). Only two tumors did not react with these 3 antibodies. We conclude that it is now possible to determine the nature of nearly all undifferentiated tumors on paraffin-embedded biopsy specimens.