Prolactin dependence in human breast cancers

Thyroid Diseases and Breast Cancer

Epidemiological studies aimed at defining the association of thyroid diseases with extra-thyroidal malignancies (EM) have aroused considerable interest in the possibility of revealing common genetic and environmental factors underlying disease etiology and progression. Over the years, multiple lines of evidence indicated a significant relationship between thyroid carcinomas and other primary EM, especially breast cancer. For the latter, a prominent association was also found with benign thyroid diseases. In particular, a meta-analysis revealed an increased risk of breast cancer in patients with autoimmune thyroiditis, and our recent work demonstrated that the odds ratio (OR) for breast cancer was raised in both thyroid autoantibody-positive and -negative patients. However, the OR was significantly lower for thyroid autoantibody-positive patients compared to the negative ones. This is in agreement with findings showing that the development of thyroid autoimmunity in cancer patients receiving immunotherapy is associated with better outcome and supports clinical evidence that breast cancer patients with thyroid autoimmunity have longer disease-free interval and overall survival. These results seem to suggest that factors other than oncologic treatments may play a role in the initiation and progression of a second primary malignancy. The molecular links between thyroid autoimmunity and breast cancer remain, however, unidentified, and different hypotheses have been proposed. Here, we will review the epidemiological, clinical, and experimental data relating thyroid diseases and breast cancer, as well as the possible hormonal and molecular mechanisms underlying such associations.

Androgen regulation of prolactin-receptor gene expression in MCF-7 and MDA-MB-453 human breast cancer cells

Lactogenic hormones which bind to the PRLR are likely to be growth-stimulatory in human breast-cancer cells. Oestrogen and progesterone control cellular expression of the PRLR; however, elevated androgen levels in some breast-cancer patients raised the possibility that androgens may also influence breast-cancer sensitivity to lactogenic hormones. This study investigated whether androgens could affect expression of the PRLR in the MCF-7 breast-cancer cell line. PRLR binding activity was increased approximately 2-fold by treatment for 24 hr with 10 nM R1881, TEST, DHT, MPA and ORG 2058. Northern analysis indicated that DHT also increased the level of PRLR mRNA. The antiprogesterone, RU 38486, displaced tritiated ORG 2058 binding but not tritiated DHT binding to MCF-7 cells; it completely antagonized ORG 2058 and partially antagonized R1881 induction of the PRLR, but had no effect on induction by DHT. The anti-androgen, RU 23908, displaced tritiated DHT binding but not tritiated ORG 2058 binding, and antagonized DHT and R1881 induction of PRLR but not induction of the PRLR by ORG 2058. These data indicated that ORG 2058 acting via the PR and DHT acting via the AR were able to induce PRLR expression in MCF-7 cells. In MDA-MB-453 cells, which express the AR but not the ER or PR, DHT and R1881 increased PRLR binding to 150% of control values at 0.1 nM. ORG 2058 was ineffective, demonstrating androgen induction of PRLR in the absence of PR and ER. These data indicate that PRLR can be regulated by androgens in MCF-7 and MDA-MB-453 human breast-cancer cells.

Biological and clinical aspects of prolactin receptors (PRL-R) in human breast cancer

PRL has a definite activity in the induction and promotion of mouse and in the growth of rat mammary tumors. We and others have found that human PRL or growth hormone (GH) had a growth promoting effect on human mammary cancer cells. It has been shown that prolactin receptors (PRL-R) which are specific for all lactogenic hormones (hPRL, hGH, hPL) are present on mammary cancer cells in long-term tissue culture and also in tumor biopsies. We found that 43% of the tumors had free PRL-R (FPRL-R) and that 72% had total PRL-R (TPRL-R) which have been desaturated in vitro. A significant correlation (Spearman test) was found between PRL-R (especially TPRL-R) on the one hand, estradiol (P less than 0.001) and progesterone receptors (P less than 0.01) on the other. The demonstration of PRL-induced proteins (PIP) might be a better sign of PRL sensitivity than the existence or PRL-R; PIP have been found by Northern blot analysis in 47% of 70 breast cancers. Overall survival (OS) and relapse-free survival (RFS) analysis with a median duration of follow-up of 5.3 yr showed that TPRL-R had a significant prognostic value only in node positive patients (chi 2 = 5.61, P = 0.02). Neither FPRL-R or TPRL-R were a significant prognostic factor when studied by Cox analysis. This confirms our previous results. Since at least some human mammary cancers appear to be PRL-dependent we carried out a multicenter randomized trial comparing as the first hormonal treatment tamoxifen (TAM) (30 mg/day) + bromocriptine (B) (5 mg/day) vs TAM + placebo. 171 patients entered this trial. No difference was observed between the two groups in response rates, duration of response or survival. Recent studies are thus in favor of a role of lactogenic hormones during the course of breast cancer. However no improvement in therapy has been observed yet. The combination of drugs to achieve a total anti-lactogenic treatment, the use of anti-PRL-R antibodies are interesting areas of research; the recent cloning of PRL-R and GH receptors may open new clinical perspectives.

Correlation between inhibitory effect on prolactin secretion and antitumor activity of new ergoline compounds on DMBA-induced tumors in rats

Five recently synthesized (355/1057, 355/1000, 355/1101, 355/1138 and FCE 21336) and 4 well-known (bromocriptine, metergoline, 1-demethylmetergoline and pergolide) prolactin-lowering ergoline derivatives and 1 ergoline (nicergoline) without antiprolactin activity were tested against 7-12-dimethyl-benzanthracene (DMBA)-induced mammary carcinomas in rats. Nicergoline did not show any activity, while the other compounds, tested at doses inhibiting prolactin secretion, proved active against established tumors and on the onset of new tumors. The activity of 3 of the new ergolines (355/1000, 355/1057 and FCE 21336) and of bromocriptine and pergolide was also tested at different oral doses and was correlated with serum prolactin levels 24 hr after the last dose. All the compounds proved highly effective, inducing 50-60% regression of the initial tumors. The inhibition of serum prolactin levels was dose-related and, for all the compounds tested except bromocriptine, a good correlation was found between doses administered and complete tumor remissions.

Prolactin receptors in human breast cancer

Prolactin receptors have been measured in 92 human breast carcinomas. Both free and total receptors (after desaturation by MgCl2) have been looked for. Free receptors have been found in 46% of the cases, total receptors in 72%. Specific binding ranges from 0.8 to 8.0%. No correlation could be found between prolactin receptors and age, weight, menopausal status and pathological features (differentiation, histoprognostic grading, cellular density). A highly significant correlation has been found between prolactin receptors on the one hand and estradiol and progesterone receptors on the other.

Circadian pattern of prolactin secretion in postmenopausal women receiving estrogen with or without progestin

The circadian rhythm of prolactin secretion was assessed in postmenopausal women before and after daily administration of ethinyl estradiol for 4 weeks given in the morning (AM) or evening (PM) or in combination with a synthetic progestin, 17-medroxyprogesterone acetate. In response to AM ethinyl estradiol, mean circulating levels of serum prolactin during sleep and awake phases of the day rose 2.5-fold compared to untreated control values. The sleep/wake ratios for serum prolactin were comparable prior to and after AM administration of ethinyl estradiol. Altered time of administration, PM ethinyl estradiol or concomitant ethinyl estradiol and progestin treatment produced similar increases in mean prolactin levels, which were not different from the level observed during AM administration of ethinyl estradiol. These findings indicate that estrogen replacement therapy, in a dosage recommended for treatment of the menopause, stimulated a sustained rise in serum prolactin over 24 hours. This enhanced release of prolactin was not influenced by the time of administration of estrogen or concomitant administration of 17-medroxyprogesterone acetate.

Prolactin receptors in human breast carcinoma

A preliminary investigation into prolactin receptors in human breast carcinomas provided strong evidence that specific binding of prolactin was occurring in at least three of the nine specimens examined (eight human breast carcinomas and one scalp metastasis). These "prolactin receptor positive" tumors were all from premenopausal patients. Three of the tumors of postmenopausal women also suggested the occurrence of specific prolactin binding but, as saturation of the receptors had not been achieved in these assays, the results require confirmation. Some general trends in the binding characteristics of the tumors of premenopausal and postmenopausal patients were also observed.

Prolactin receptors: a comparison between chloramine-T and lactoperoxidase iodination

The binding properties of chloramine-T iodinated oPRL (using a modified iodination procedure) to prolactin receptors of female rat liver membrane particles were compared with those of lactoperoxidase iodinated oPRL. The results indicated that both iodination methods provided 125I-oPRLs which were suitable for receptor binding studies. Our results suggested that chloramine-T 125I-oPRL was even better than lactoperoxidase 125I-oPRL in terms of lower nonspecific binding. The chloramine-T iodinated oPRL was used to study the prolactin receptors in rat ovaries and DMBA induced rat mammary tumors. The results showed that the amount of prolactin receptors in rat ovaries was related to the plasma level of prolactin as it had been reported in liver by other investigators. The study of prolactin receptors in rat mammary tumors indicated that the prolactin receptor content of hormone dependent mammary tumors was much higher than that of hormone independent mammary tumors.

[Mammotropic and somatotropic pituitary cells in spontaneous mammary tumor bearing C3H female mice. A quantitative electron microscope study]

Pituitaries of mammary tumor-bearing mice (C3H) were examined by quantitative electron microscopy. The results indicate that considerable modifications occur in mammotropic and somatotropic cells. Both types show an increase of the surface of the endoplasmic reticulum and a decrease of the volume of secretory granules (in percent of cytoplasmic volume), suggesting a heightened secretory activity of these cells during mammary carcinogenesis.

Hormonal sensitivity of human breast tumors in vitro: pentose-shunt activity

Recent studies indicated that response to endocrine therapy might be predicted in human breast carcinomas using the sensitivity of the pentose-shunt pathway to hormones in organ culture. Thirty breast tumors were examined using this histochemical method, and three independent assessments were made. There was poor agreement between the observers, and we consider that this test is not reproducible in its present form.

Prolactin dynamics following transphenoidal hypophysectomy for metastatic carcinoma of the breast

In nine patients who had undergone trans-sphenoidal hypophysectomy, prolactin dynamics were studied with intravenous thyrotropin releasing hormone (TRH). Residual prolactin secretory reserve was demonstrated in seven. Five patients were TRH tested both before and after trans-sphenoidal hypophysectomy. Hypophysectomy did not alter base line prolactin concentration but did decrease prolactin response to TRH from 55 ng/ml to 21 ng/ml (p less than 0.001). Post-hypophysectomy L-Dopa suppressed baseline prolactin concentrations to undetectable levels. There was no correlation between alterations in prolactin dynamics and tumor response to hypophysectomy. Trans-sphenoidal hypophysectomy is not effective in ablating prolactin secretion and serious doubts are raised about the role of altered prolactin dynamics in inducing breast cancer remission.

Demonstration of hormonal sensitivity in gynaecomastic tissue by thymidine incorporation in vitro

Gynaecomastic tissue from six patients were tested for oestrogen and testosterone sensitivity as measured by thymidine incorporation in tissue fragments in vitro. The DNA synthesis of the cultures was increased in tissue from five out of the six patients under the influence of oestrogen, whereas it was increased in tissue from only one patient under the influence of testosterone. The results are discussed in relation to the medical histories of the patients and hormonal excretion studies done by others.

Effect of metroclopramide on serum prolactin levels in humans

The effect of acute and chronic administration of metoclopramide on serum prolactin levels in normal subjects was studied. Metoclopramide 10 mg i.v. induced a prompt rise in serum prolactin levels in all subjects. At 180 min the levels remained high. Prolactin levels were markedly elevated during a 5 day course of treatment with metoclopramide in six subjects. It is suggested that metoclopramide could be used in the functional exploration of the hypothalamic-pituitary axis.

DNA synthesis of human, mouse, and rat mammary carcinomas in vitro: influence of insulin and prolactin

Carcinomatous mammary tissues, derived from six spontaneously arising mouse mammary tumors, six DMBA-induced rat mammary tumors, and 26 biopsy specimens of human breast tumors, were processed into slices and each tumor was inidvidually cultured for two days in Medium 199. The influence of bovine insulin (5.0 mug/ml) and ovine prolactin (10.0 mug/ml) on H3-thymidine incorporation into DNA was determined on the cultured tumor slices. Insulin consistenly (p less than 0.05-0.01) increased the incorporation of H3-thymidine into DNA of the organ cultures of mouse, rat, and human mammary carcinoma slices. The stimulatory effect of insulin was quantitatively more prominent in the mouse tumor slices than in the rat or human slices. The addition of prolaction to the insulin-containing culture medium further increased significantly (p less than 0.001) the incorporation of H3-thymidine into DNA of rat mammary carcinoma slices but had no significant effect on cultures of either mouse or human mammary carcinomas. The addition of prolactin to insulin and hydrocortisone-enriched medium containing slices of 20 individually cultured human breast carcinomas did not significantly influence the mean incorporation of H3-thymidine into DNA. However, a very small fraction (approximately equal to 15%) of these human breast carcinomas responded to prolactin by increasing the incorporation of H3-thymidine into DNA to a degree quantitatively comparable to the prolactin-sensitive, DMBA-induced rat mammary carcinoma. These results suggest that a very small fraction of human breast malignancies may respond to the growth-stimulatory effects of prolactin, but that the vast majority mimic more closely the prolactin-independent mouse mammary carcinoma.

Hormones and gynecologic cancer

Available basic information about the regulation of rates of production, blood levels, intracellular metabolism, and action of steroid hormones and prolactin is reviewed and related to high-risk factors and therapeutic procedures applicable to gynecologic cancer.

Effect of acute and chronic neuroleptic therapy on serum prolactin levels in men and women of different age groups

A single fasting level of serum prolactin was measured in each of sixty control subjects and eighty-three psychiatric patients of both sexes who had been on neuroleptic therapy for 2-4 weeks (acute treatment) or at least 5 years (chronic treatment) and who were aged either 17-45 or 48-85 years. All groups of patients had significantly higher mean prolactin levels than controls. Gender, age group of women, and exposure to acute or chronic treatment were significant variables determining the magnitude of neuroleptic-induced elevation of prolactin. In some of the groups, dose, duration of chronic therapy, and concomitant administration of anticholinergic drugs also influenced prolactin levels. Whereas all acutely treated women had prolactin values above the control range, one out of twelve (8-3%) of the women aged 17-45 years and six out of fourteen (42-9%) of the women aged 48-85 years who were under chronic treatment had normal values. Normal prolactin levels were also found in five out of sixteen (31-2%) of the acutely treated and nine out of twenty-four (37-5%) of the chronically treated men aged 17-85 years.

Plasma prolactin responses to thyrotropin-releasing hormone in patients with breast cancer

Plasma human prolactin levels were measured by homologous radioimmunoassay in patients with primary breast cancer and in normal women of similar age. In normal controls mean (+/- SEM) basal plasma prolactin levels were 11.9 +/- 1.5 ng/ml and intravenous injection of synthetic thyrotropin-releasing hormone (TRH), 500 mug, caused a significant rise in plasma prolactin in all subjects examined with a maximum response of 52.6 +/- 3.3 ng/ml (mean +/- SEM). Markedly high plasma prolactin levels and exaggerated plasma prolactin responses to TRH were demonstrated in some patients with breast cancer. However, mean basal plasma prolactin levels and mean plasma prolactin increments following TRH in patients with breast cancer did not differ significantly from those in normal subjects. Plasma prolactin responses to TRH were slightly blunted during the administration of androgen in patients with breast cancer. These results suggest that some of the patients with primary breast cancer have abnormal prolactin secretion.

An assessment of the effects of hormones on short term organ cultures of human breast carcinomata

Twenty-eight mammary carcinomata were maintained in organ culture in the presence of various hormones. The effects of the hormones have been assessed histologically by estimation of total dehydrogenases activity of the pentose glycolytic pathway and by the incorporation of tritiated thymidine or uridine into DNA or RNA. No significant effects on tumour cell activity due to hormones have been observed.

Hypothesis: breast cancer regression under oestrogen therapy

Recent reports have thrown doubt on both of the major mechanisms which have been suggested for the regression of breast cancer under high-dosage oestrogen therapy-a direct effect on binding sites and an indirect inhibition of prolactin release. A searching review on the clinical response of 407 patients with advanced breast cancer treated by oestrogen therapy under my direction showed certain anomalies, including age determined tumour inhibition and stimulation, dose dependence of tumour inhibition and stimulation, differential site sensitivity, and tumour regression with oestrogen withdrawal. The hypothesis usually postulated to explain these anomalies is that the tumour may in the same individual be composed of multiple genetically distinct clones of cells. It is suggested instead that the effect of high-dosage oestrogen therapy in breast cancer may depend critically on the absolute and relative concentrations of prolactin and oestrogen actively available at the tumour. On this basis the clinical manifestation of tumour stimulation in response to oestrogen administration suggests that the oestrogen concentration at the target is inadequate. Differences in site sensitivity in the same patient may depend on tumoral factors such as the level of oestradiol and prolactin binding receptors in the tissue.