Detection of metastatic tumour cells in routine bone marrow smears by immuno‐alkaline phosphatase labelling with monoclonal antibodies

Summary. The present study describes 11 cases (10 carcinomas, one rhabdo‐myosarcoma) in which immuno‐alkaline phosphatase labelling with monoclonal antibodies was used to demonstrate metastatic cells in routine smears of aspirated bone marrow. Carcinoma cells were detected using antibodies against epithelial cytokeratins, milk fat globule membrane antigen and carcinoem‐bryonic antigen, and rhabdomyosarcoma cells with monoclonal anti‐desmin. In four of the carcinoma cases it had not been possible to identify malignant cells in routinely stained marrow smears, whilst the case of disseminated rhabdomyosarcoma had initially been diagnosed (and treated) as a case of acute lymphoblastic leukaemia. The anti‐cytokeratin antibody was found to be the most valuable of the anti‐epithelial reagents used, since it labelled malignant cells in all of the 10 cases of carcinoma and gave the strongest reactions. These results suggest that immunocytochemical labelling should be used in cases of suspected carcinoma whenever conventional examination of marrow smears yields negative results, and furthermore (as illustrated by the case of rhabdomyosarcoma) that the technique is of value for identifying the true nature of poorly differentiated neoplasms in bone marrow.