Detection of a soluble antigen defined by monoclonal antibody 83D4 in serous effusions associated with breast carcinoma.

Monoclonal antibody (MoAb) 83D4 was generated by immunization with cell suspensions obtained from sections of formol-fixed paraffin embedded human breast cancer. It recognized an antigen expressed in breast carcinomas but not in normal breast tissue. Pleural and ascitic fluids from 66 patients were studied by an 83D4 heterologous sandwich radioimmunoassay (SRIA) using solid-phase immobilized wheat germ agglutinin to detect the 83D4 soluble antigen. Using a cutoff level of 5 units/ml of 83D4 antigen, higher values were found in 22 of 27 breast cancer-associated effusions (mean = 10.72 +/- 6.80 units/ml). The 20 nonmalignant effusion fluids tested showed lower values (mean = 1.16 +/- 1.49 units/ml, P less than 0.001). The antigen was undetectable or present in low levels in effusions from patients with hematologic malignancies. When SRIA results were compared with conventional cytologic diagnosis in breast-cancer effusions, elevated levels of 83D4 soluble antigen were found in all patients (8 of 8) in whom malignant cells had been detected, in 4 of 8 patients with the diagnosis of "suspected malignancy," and in 10 of 11 patients with negative cytologic findings. Using an immunoglucosidase method on cell smears of various origins, MoAb 83D4 stained metastatic cells of breast and ovary carcinomas but did not reactive with mesothelial cells and other normal or malignant cell types. These results suggest that quantitation of the 83D4 soluble antigen may be used to improve the diagnosis of cancer in serous effusions.