Detection of micrometastases from primary breast cancer.

The monoclonal antibody LICR-LON-M8 was used in a series of experiments to determine how an immunohistochemical technique could be used as a diagnostic test for micrometastatic disease in patients with operable, primary breast carcinoma. Optimal tissue and antigen preservation was obtained with fixatives containing either picric acid or a heavy metal such as mercury to allow staining with the monoclonal antibody diluted to 1:12,000 to 1:16,000 from unpurified mouse ascites. Tissue affected by primary and metastatic disease stains in a characteristic fashion, which is distinct from benign breast tissue. All the ductal tumours stained positively for malignant cells with the monoclonal antibody preparation. Within the bone marrow, occasional granulocytes and granulocyte precursors stained positively if the endogenous peroxidase activity was incompletely blocked. These cells were readily differentiated from tumour cells on cytologic examination. With these monoclonal antibody and immunohistochemical staining techniques it may now be possible to detect early micrometastatic disease in the bone marrow of patients with primary breast cancer.