Beta-endorphin, steroids, and prolactin. Immunoassay in breast cysts and blood.

Circulating levels and cyst fluid concentrations of beta-endorphin (beta-EP), estradiol, progesterone, and prolactin were measured by radioimmunoassays in 10 premenopausal women with gross breast cysts. In addition, aspirates and frozen tissue sections from cystic lesions were investigated immunocytochemically for a possible beta-EP production. Epithelia of dilated ducts, smaller cysts, and hyperplastic lesions without atypia showed a strong positive reaction in the cytoplasm. In apocrine metaplasia, this staining was concentrated in the apical region. The staining intensity in atypical hyperplasia was diminished. Occasionally, normal duct and lobular epithelia exhibited positive beta-EP immunostaining. Levels of beta-EP, estradiol, and progesterone in the cyst fluid were significantly higher than in blood, but no significant differences were observed for prolactin. The ratios of progesterone to estradiol, estradiol to prolactin, and progesterone to prolactin in the cyst fluid were considerably higher than in blood. This suggests that beta-EP and steroid hormones are secreted from the lining epithelia into the breast cysts.