Immunofluorescent monoclonal antibody detection of breast cancer in bone marrow: sensitivity in a model system

We have previously shown that occult micrometastases can be detected in the bone marrow of breast cancer patients using a panel of epithelial specific monoclonal antibodies in an indirect immunofluorescent assay. The sensitivity of this assay has been examined using cells from an established human breast cancer cell line (MCF-7) mixed with normal bone marrow at various dilutions from 400 cancer cells/10(6) marrow cells (400:10(6] to 10:10(6). MCF-7 cells were detected at the lowest concentration studied, namely 10:10(6). The number of fluorescent labeled MCF-7 cells counted at each concentration was related to the concentration by a simple nonlinear statistical model. At the concentration of 10:10(6), the model shows that this technique has the sensitivity to detect between two and four MCF-7 cells 95% of the time. Moreover, by extrapolation, the model predicts that even at the very low concentration of 2:10(6), there is a 95% chance of detecting one cancer cell. Therefore, this assay may be a very sensitive method for detecting cancer cells in the bone marrow in vivo.