MAM-6 antigen, a new serum marker for breast cancer monitoring.

Almost all carcinomas contain a cell surface antigen, MAM-6, which has been defined by several monoclonal antibodies, including 115D8 (Hilkens et al., Int. J. Cancer, 34: 197-206, 1984). A quantitative sandwich radioimmunoassay, using 115D8 as catcher and as tracer antibody, has been developed to detect MAM-6 in serum. To quantitate the MAM-6 level, pooled human milk was used as a standard, and arbitrary units were chosen. Less than 5% of the sera of apparently healthy individuals contained more than 5 units/ml. In sera of patients with benign breast lesions, the same low levels were detected. However, concentrations over 5 units/ml were found in 24, 21, 43, and 79% of the sera of patients with pathological Stages I, II, III, and IV breast cancer, respectively. MAM-6 levels were also increased in almost all sera tested from patients with advanced stages of ovarian carcinoma, but in a low percentage of sera from patients with other advanced cancers. A longitudinal study was carried out to test the MAM-6 assay as clinical marker to monitor the therapeutic response of breast cancer. Increasing or decreasing MAM-6 serum levels correlated in 93% of the cases with breast cancer progression or regression, indicating that the assay can be used to monitor the course of the disease during therapy. In some breast cancer patients, elevated MAM-6 levels were observed prior to any clinical indication of tumor recurrence.