FACTORS EFFECTING THE MEASUREMENT OF TUMOR-ASSOCIATED MUC1 MUCINS IN SERUM

MUC1 epithelial mucins are produced by both normal and malignant epith elial cells. Serum proteins reactive with monoclonal antibodies agains t MUC1 mucins were studied using several techniques. Separation of pro teins by native PAGE showed that anti-MUC1 core protein antibodies rea cted with a high M(r) mucin but also with a 70-kD protein (p70) in nor mal women and women with ovarian cancer. After purification by gel fil tration, p70 was not reactive in a double-determinant ELISA (CASA) and only weakly reactive in an inhibition assay. Serum CASA levels increa sed during pregnancy but p70 disappeared. Neuraminidase treatment of s erum resulted in a greater increase in CASA in normal women and in ova rian cancer patients with low initial CASA than in ovarian cancer pati ents with high CASA and pregnant women (p < 0.05). These findings sugg est that pregnancy and ovarian cancer-derived mucins are less heavily sialylated than mucin derived from normal tissues. An inhibition assay was developed which was more sensitive, but provided no diagnostic ad vantage over CASA. MUC1 is present in the serum of all women, reactivi ty in assays utilizing core protein antibodies is probably dependent n ot only on molar concentration but on the degree of exposure of peptid e epitopes.