Prolactin Response to Thyrotropin-Releasing Hormone in Early and Advanced Human Breast Cancer

The forgotten effects of thyrotropin-releasing hormone: Metabolic functions and medical applications

Thyrotropin-releasing hormone (TRH) causes a variety of thyroidal and non-thyroidal effects, the best known being the feedback regulation of thyroid hormone levels. This was employed in the TRH stimulation test, which is currently little used. The role of TRH as a cancer biomarker is minor, but exaggerated responses to TSH and prolactin levels in breast cancer led to the hypothesis of a potential role for TRH in the pathogenesis of this disease. TRH is a rapidly degraded peptide with multiple targets, limiting its suitability as a biomarker and drug candidate. Although some studies reported efficacy in neural diseases (depression, spinal cord injury, amyotrophic lateral sclerosis, etc.), therapeutic use of TRH is presently restricted to spinocerebellar degenerative disease. Regulation of TRH production in the hypothalamus, patterns of expression of TRH and its receptor in the body, its role in energy metabolism and in prolactin secretion are addressed in this review.

Endocrinological Study of the Dopaminergic Regulation of Prolactin Release in Metastatic Breast Cancer

Aims and Background

Prolactin (PRL) may be a growth factor for breast cancer. Abnormally high levels of PRL have been proven to be associated with a poor prognosis in metastatic breast cancer. However, most studies have been limited to the evaluation of basal levels of PRL rather than its response to the classical endocrine dynamic tests. This study was performed to analyse the dynamic secretion of PRL under stimulatory and inhibitory tests in metastatic breast cancer.

Methods

The study included 10 untreated metastatic breast cancer women, who were evaluated after the classical stimulatory and inhibitory tests for PRL secretion with the antidopaminergic agent Metoclopramide (10 mg iv as a bolus) and with L-dopa, respectively. Serum levels of PRL were measured by RIA before and at subsequent intervals after drug administration. PRL levels were considered to be elevated when they were higher than 25 ng/ml.

Results

Abnormally high basal levels of PRL were seen in 6/10 patients. L-dopa was unable to inhibit PRL secretion, whose mean concentrations paradoxically significantly increased in response to L-dopa, with values comparable to those observed after the classical stimulatory test with metoclopramide.

Conclusions

This study confirm the existence of hyperprolactinemia associated with metastatic breast cancer. In addition, by showing a paradoxical rise of PRL in response to L-dopa, which inhibits PRL secretion in physiological conditions, this study would suggest that breast cancer-related hyperprolactinemia may depend at least in part on endogenous disease-related neuroendocrine alterations.

Correlation between Changes in Prolactin and Melatonin Serum Levels after Radical Mastectomy

Both prolactin (PRL) and melatonin (MLT) (the most important pineal hormone) have been shown to play a role in regulating breast cancer growth. The present study was carried out to investigate the relationship between PRL and MLT secretions in human breast cancer. Twenty-four women with breast cancer, at clinical stage T1-2 N0-2 M0, were evaluated before and after radical mastectomy. As controls, 14 women who underwent surgery for reasons other than neoplastic disease were included in the study. PRL and MLT serum levels were measured by RIA before and 15 days after surgery. There were no significant differences in mean PRL serum levels between patients and controls; mean MLT serum values were significantly higher in patients than in controls. In no control subject was PRL affected by surgery. In contrast, 13/24 breast cancer women showed high PRL levels after mastectomy; the PRL rise induced by surgery was significantly higher in patients without axillary node involvement. MLT was not affected by mastectomy in 13 patients, whereas it was enhanced in 5 women and decreased in the last 6 cases. No significant correlation was seen between PRL and MLT changes induced by mastectomy. The present study shows that radical mastectomy influences PRL and MLT secretions, however, its clinical significance remains to be established.

Serum immunoreactive and bioactive lactogenic hormones in advanced breast cancer patients treated with bromocriptine and octreotide

6 patients with advanced breast cancer who had failed first and second line endocrine therapies received bromocriptine (1.25-2.5 mg twice daily per os) and octreotide (Sandostatin) via a continuous subcutaneous infusion (200-400 micrograms/24 h) until disease progression. Pre-treatment 24-h profiles of serum lactogenic hormones and their response to standard provocative tests were established and repeated at 2 weeks, and 3 and 6 months (or at tumour progression). Immunoreactive prolactin (ir-PRL), growth hormone (ir-GH) and insulin-like growth factor I (IGF-I) were measured by radioimmunoassay and bioactive lactogenic hormone levels (BLH) were estimated using the Nb2 rat lymphoma cell bioassay. Before treatment all patients showed episodic secretion of ir-PRL, ir-GH and BLH and provocative stimuli resulted in a peak of ir-GH and BLH maximal between 60 and 90 min after injection but no change in ir-PRL. After 2 weeks of treatment, ir-PRL levels were reduced to below the limit of detection in all 6 patients. Peaks of ir-GH and BLH were still apparent, although much reduced. Immunoreactive PRL continued to be profoundly suppressed in 3 of the 4 patients who remained on treatment for 3 to 6 months. Small pulses of ir-GH were still detectable in these patients with which BLH was, again, well correlated. After 2 weeks of treatment, serum IGF-I levels were reduced by 9-54% of the pretreatment values and generally remained suppressed throughout treatment. Clinically, 4 patients did not show disease progression for periods of up to 6 months and side-effects were minimal.

Effects of radical mastectomy on prolactin blood levels in patients with breast cancer

The role played by PRL in human breast cancer is still obscure. Several observations, however, demonstrated that antitumor therapies for breast cancer are associated with changes in PRL secretion, clinical significance of which remains to be determined. The present investigation was carried out to further clarify the effects of mastectomy on PRL levels in breast cancer women. The study included 34 patients at clinical stage T1-2N0-2M0 treated with radical mastectomy. In each patient, venous blood samples were drawn before, and 15 days, 1 month, 45 days, 2 months and 3 months after surgery to determine PRL serum levels. As controls, 14 women surgically treated for reasons other than neoplastic disease were included in the study. Mastectomy was followed by hyperprolactinemia in 18 of the 34 cases (52.9%). PRL remained elevated for at least 1 month, and it became normal within 2 months. On the contrary, no PRL increase was seen in controls. Among breast cancer women, PRL increase was irrespective of the type of surgery, the histology of the tumor and the menopausal status. In contrast, PRL increase was significantly higher in patients without node involvement and with negative hormonal receptors, with respect to that observed in cases with node involvement and positive receptors, respectively. The mechanisms by which mastectomy induces enhanced PRL secretion are still obscure. They might depend, however, on changes in feed-back systems operating in the regulation of PRL secretion, due to the removal of a target organ for PRL itself. Longitudinal studies, by evaluating the percentage of relapse either in patients with surgery-induced hyperprolactinemia or in those with normal hormonal values, will be needed to clarify the prognostic significance of the enhanced PRL secretion induced by mastectomy.