Detection of alpha-lactalbumin in breast lesions and relationship to estrogen receptors and serum prolactin.

Alpha-lactalbumin, the B protein of lactose synthetase secreted by the mammary epithelial cells, was isolated and purified from fresh human milk and injected into rabbits for antibody production. Indirect immunofluorescence (IIF) was done on various types of breast lesions to assess the relationship, if any, between histologic type and production of alpha-lactalbumin. Fifty percent of fibroadenomas and fibrocystic disease and 63% of infiltrating ductal carcinoma showed positive reaction. No false positives were found on IIF of alpha-lactalbumin of several tumors of nonmammary tissue. These findings suggest that IIF for alpha-lactalbumin may be helpful in ascertaining the site of origin of metastatic breast tumors. However, serum alpha-lactalbumin was detected by radioimmunoassay in only 10% of women with infiltrating ductal carcinoma, indicating that this may not be a useful marker for the presence of breast cancer at least by the method employed. This discrepancy between serum and tissue alpha-lactalbumin may be due to the short half-life of serum alpha-lactalbumin or to the lack of secretion of the protein into the blood. There was no apparent relationship between the presence of estrogen receptors or serum prolactin and alpha-lactalbumin in the 27 mammary carcinomas investigated.