A comparison of serum and breast duct fluid‐immunoassayable prolactin and growth hormone with bioassayable lactogenic hormones in healthy women and patients with cystic breast disease

Abstract Serum and breast fluid obtained by nipple aspiration were collected from 46 healthy premenopausal women, and 36 patients with cystic breast disease and cyclical mastalgia of similar age. Serum prolactin and growth hormone levels determined by radioimmunoassay were similar in the two groups, but the patients showed a significant elevation in bioactive lactogenic hormones (prolactin plus growth hormone) as determined by the Nb2 rat lymphoma cell bioassay ( P < 0.001). The radioimmunoassayable prolactin levels in breast fluid were extremely variable; there was a trend towards higher concentrations in the cystic breast disease patients, but this just failed to achieve statistical significance ( P = 0.06). Immunoreactive growth hormone was rarely detected in nipple aspirates obtained from either the patient or control groups. The mean breast fluid bioactive lactogenic hormone level was significantly higher in the cystic breast disease patients than in the normal controls ( P < 0.001); also ten of 46 (22%) controls, but only two of 36 (6%) patients had no detectable bioactivity. It is concluded that lactogenic hormone bioactivity, when assessed by the Nb2 cell assay, is indicative of an endocrine abnormality which is associated with benign breast disease, and is reflected in breast duct fluid, but is not identified by the conventional radioimmunoassays.