Sensitivity of Immunocytochemical Detection of Breast Cancer Cells in Human Bone Marrow

We have previously shown that occult micrometastases can be detected in the bone marrow of breast cancer patients, at the time of initial treatment, using a panel of epithelial specific monoclonal antibodies indirectly labeled with fluorescein. These monoclonal antibodies permit us to detect cancer cells at a concentration of two/million normal bone marrow cells. Immunofluorescence carries the disadvantage that detailed morphological examination of detected cells cannot be accomplished. A modification of the alkaline phosphatase anti-alkaline phosphatase method has been used to detect cancer cells and to observe their mor phology in human bone marrow. The sensitivity of this method has been examined using an established human metastatic breast cancer cell line (MCF-7) mixed with normal bone marrow cells at various dilutions from 400 cancer cells/106 marrow cells to 10 cancer cells/10⁶ marrow cells. The number of immunocytochemically stained MCF-7 cells counted at each concentration was related to the concentration by a simple nonlinear statistical model. At a concentration of 10 cancer cells/106 bone marrow cells, the model shows that this method has the sensitivity to detect between four and six MCF-7 cells 95% of the time. Extrapolation, using this model, predicts that at the very low concentration of one cancer cell/ IO6marrow cells, there is a 95% chance of detecting the cancer cell. This assay may be a very sensitive method for detecting cancer cells in the bone marrow of breast cancer patients.