Use of monoclonal antibody B72.3 as a marker of metastatic carcinoma cells in neoplastic effusions

The value of monoclonal antibody B72.3 as a diagnostic discriminator between mesothelioma and carcinoma cells in malignant effusions was assessed using the ABC method in a series of cell blocks prepared from centrifuged fluids. These were obtained from either pleural or peritoneal neoplastic effusions in patients with histologically verified malignant mesothelioma (n:10) or carcinoma (n:20). Reactivity with MAb B72.3 in at least 10% or more of tumour cells was found in 16 (80%) out of 20 metastatic carcinoma, whereas 2 mesotheliomas displayed positive immunostaining in less than 5% and approximately 20% of the malignant cells respectively. Reactive mesothelial cells were consistently non-immunostained. These results suggest that B72.3 positivity in greater than 10% of tumour cells is certainly indicative, but not absolutely diagnostic, of a metastatic origin of malignant effusions.