Prolactin and total lactogenic hormone measured by microbioassay and immunoassay in breast cancer

Basal prolactin (PRL) and total lactogenic hormone (TLH) levels were measured using a new microbioassay (BA) and conventional immunoradiometric assay (IRMA) in patients with breast cancer and compared to an age-matched control group. No significant differences were found using the IRMA, but BA lactogenic levels were significantly elevated in breast cancer patients compared controls, leading to a markedly elevated BA/IRMA ratio for both PRL (2.7 vs 1.4, P less than 0.0001) and TLH (2.8 vs 1.4, P less than 0.0001) which was greatest for postmenopausal women. Using the mean +2 standard deviations as the upper limit of normal, there was no significant difference between breast cancer patients and controls for IRMA, but BA and BA/IRMA PRL levels were elevated in 42% and 61% of the patients, respectively. There was a weak negative correlation of BA and IRMA PRL with age for normals (r = -0.53 for both) but no correlation was evident for breast cancer patients (r = 0.06 and -0.13, respectively) implying a sustained absolute and relative bioactive hyperprolactinaemia at all ages. These results show increased lactogenic bioactivity in breast cancer and suggest that different forms of bioactive prolactin undetected by IRMA (or enhancing serum factors) are present in the sera of these patients.