A sensitive and specific radioimmunoassay for human
alpha-lactalbumin, a milk protein, has been developed in order to examine the effect of
prolactin on the human breast in normal and diseased states. Samples of milk from nursing mothers and from men and women with
galactorrhea were found to contain milligram concentrations of this
protein. In serum, 8 of 25 normal men and 18 of 44 normal women had detectable concentrations of
alpha-lactalbumin. Significantly higher levels of
alpha-lactalbumin were found in 17 of 19 women during pregnancy who were not actively lactating. All nursing mothers were found to have distinctly elevated serum
alpha-lactalbumin concentrations. In a group of 17 female patients with
phenothiazine induced
prolactin elevations (mean 29.4 ng/ml), the mean serum
alpha-lactalbumin of 17.3 ng/ml was significantly higher than in normal female volunteers. Patients with
gynecomastia were not noted to have elevated
alpha-lactalbumin. In vitro, homogenates of normal breast and
carcinoma tissue from the same individuals revealed that in 9 of 17 patients
alpha-lactalbumin was present in higher concentrations in normal than in cancerous tissue. Overall,
alpha-lactalbumin was found in 48.5% of homogenates and 41% of organ cultures of normal breast tissue from
cancer patients. In contrast, it was present in only 19% of homogenates and 21% of cultures of
carcinoma tissue, indicating that the
cancer tissue may lose its ability to produce
alpha-lactalbumin. Differences in
biologic behavior were found in some
tumors. In 2 cases homogenates of
breast cancer tissue had much higher concentrations of
alpha-lactalbumin than the normal tissue, and in 3 of 33
tumors studied in organ culture
prolactin increased
alpha-lactalbumin output.