Breast cancer diagnosed during pregnancy or 1 to 2 years after birth often occurs at a late stage. Little is known about tumor characteristics in the high-risk period shortly after a childbirth. We here explore whether stage of disease differs according to timing of births. Results are based on 22,351 Norwegian breast cancer patients of parity 0 to 5, ages 20 to 74 years. The proportion of stage II to IV tumors was considerably higher among parous than nulliparous women at age <30 years (52.7% versus 36.8%, P = 0.009), but similar or lower in other age groups ( P interaction = 0.029). In general, the largest proportion of stage II to IV tumors was found among women diagnosed during pregnancy or <2 years after birth. However, among women with late-age births (first or second birth ≥30 years, third birth ≥35 years), as well as women with an early second birth (<25 years), the proportion with advanced disease was rather similar or even higher among those diagnosed 2 to 6 years after birth (49.3-56.0%). The association between clinical stage and time since birth reached statistical significance among women with a late first or second birth and among all triparous women ( P ≤ 0.032). The subgroups with a high proportion of advanced disease 2 to 6 years after birth corresponded quite well to those previously found to have the most pronounced transient increase in risk after birth. Thus, pregnancy hormones may have a progressive effect on breast cancer tumors in addition to a possible promoting effect. A potential effect of prolactin is discussed. (Cancer Epidemiol Biomarkers Prev 2006;(15)1:65–9)

https://cebp.aacrjournals.org/content/cebp/15/1/65.full.pdf

Clinical stage of breast cancer by parity, age at birth, and time since birth: a progressive effect of pregnancy hormones?

Exogenous prolactin is mitogenic and antiapoptotic in breast cancer cells, and overexpression of autocrine prolactin cDNA in breast cancer cell lines has been shown to stimulate their growth and to protect against chemotherapy-induced apoptosis. We examined the effects of the 'pure' prolactin receptor antagonist Δ1–9-G129R-hPrl (Δ1–9) on the breast cancer cell number and clonogenicity, alone and in combination with chemotherapy. The effects of doxorubicin, paclitaxel and Δ1–9 on the growth of breast cancer cell lines (MCF-7, T47D, MDA-MB-453, MDA-MB-468 and SK-BR-3) in monolayer culture were assessed by the sulphorhodamine B assay. Effects on clonogenicity were assessed by soft agar assay for the cell lines and by the mammosphere assay for disaggregated primary ductal carcinoma in situ samples. Dual-fluorescence immunocytochemistry was used to identify subpopulations of cells expressing the prolactin receptor and autocrine prolactin. Δ1–9 as a single agent had no effect on the cell number in monolayer culture, but potentiated the cytotoxic effects of doxorubicin and paclitaxel. Doxorubicin accordingly induced expression of prolactin mRNA and protein in all five breast cancer cell lines tested. Δ1–9 alone inhibited the clonogenicity in soft agar of cell lines by ~90% and the mammosphere forming efficiency of six disaggregated primary ductal carcinoma in situ samples by a median of 56% (range 32% to 88%). Subpopulations of cells could be identified in the cell lines based on the prolactin receptor and prolactin expression. Autocrine prolactin appears to act as an inducible survival factor in a clonogenic subpopulation of breast cancer cells. The rational combination of cytotoxics and Δ1–9 may therefore improve outcomes in breast cancer therapy by targeting this cell population.

/pdf/prolactin-receptor-antagonism-reduces-the-clonogenic-48edfnuh96.pdf

Prolactin receptor antagonism reduces the clonogenic capacity of breast cancer cells and potentiates doxorubicin and paclitaxel cytotoxicity.

Historically, hyperprolactinaemia has been considered of low toxicological relevance when detected in toxicity studies, and even mammary carcinogenesis induced in the rat by prolactin excess has been considered of no relevance to humans. However, recent findings from human epidemiology and molecular biology suggests that prolactin is a risk factor for human breast cancer, and probably prostate cancer. Therefore, this new evidence should be considered in the various decisions to develop and license a new drug or chemical if the compound causes hyperprolactinaemia. This emerging evidence suggests that prolactin can also be produced locally from human breast cancer cells, and that, regardless of source (ie, pituitary or autocrine/paracrine production from cancer cells), prolactin is mitogenic, stimulates proliferation and suppresses apoptosis in breast and prostate cancer cells. This review outlines the evidence that hyperprolactinaemia should be considered a toxicological adverse effect and concludes that prolactin-induced rodent mammary carcinogenesis is relevant to humans and is not species-specific. The effects of prolactin on the prostate gland are also discussed; hyperprolactinaemia may be an additional risk factor for prostate cancer and this also requires consideration in toxicological risk assessments. The implications of increased prolactin secretion as an adverse effect for regulatory toxicology of drugs and chemicals, and in high risk patients receiving therapeutic drugs with hyperprolactinaemic side effects, is discussed. Alteration of prolactin level is also a novel mechanism that requires consideration in endocrine disruption research, since both endogenous oestrogens and also xenoestrogens stimulate prolactin secretion or affect prolactin receptors.

Hyperprolactinaemia as an adverse effect in regulatory and clinical toxicology: role in breast and prostate cancer.

Prolactin-induced mammary carcinogenesis in rodents, particularly rats, is often stated to be of low toxicological relevance to humans. This opinion appears to have developed from a number of lines of cited evidence. Firstly, there had been long experience of use of dopamine antagonists (that increase prolactin) in human medicine and no evidence of an increase in breast cancer incidence or risk had been reported. Secondly, dopamine agonists (that lower prolactin) had been shown to have no effect in human breast cancer treatment. Thirdly, the actions of prolactin were considered different between rodents and humans. However, recent evidence now suggests that prolactin has a major role in human breast cancer, and the similarity of mechanism with the rodent suggests that prolactin-mediated mammary carcinogenesis in rodents could be of much higher toxicological relevance to humans than previously thought. Large epidemiology studies have upgraded a limited database and shown that dopamine antagonists (both antipsychotics and anti-emetics) increase breast cancer risk, that hyperprolactinaemia is consistently associated with human breast cancer growth, development and poor prognosis, and that prolactin is indeed a mitogen in human breast cancer cells that suppresses apoptosis and upregulates BRCA1. It is now clear that initial studies giving dopamine agonists to breast cancer patients had no effect because breast cancer cells also produced prolactin independently of the pituitary, which remained uncontrolled and unrecognized in early clinical studies. The evidence for the role of prolactin in human breast cancer is now strong and consistent, and is discussed and related to the risk assessment of drugs and chemicals. The conclusion is that it is invalid to suggest that prolactin-induced mammary carcinogenesis in rodents is of low relevance to humans because prolactin can induce an adverse response in the mammary tissue of both rodents and humans alike. Drugs and chemicals causing rodent prolactin-induced mammary carcinogenesis may therefore pose a risk to humans via the same mechanism if exposures also increase prolactin secretion in humans.

Human relevance of rodent prolactin-induced non-genotoxic mammary carcinogenesis: prolactin involvement in human breast cancer and significance for toxicology risk assessments.

Pregnancy-associated breast cancer, which is defined as all breast cancer diagnosed during pregnancy or within the following year, is a relatively rare finding. Due to the particular difficulties in the diagnosis of breast cancer during this period, pregnant women tend to present more advanced disease at diagnosis. Four cases of pregnancy-associated breast cancer referred to our Institute are described as a contribution to the knowledge of this disease.

Pregnancy-associated breast cancer.

Despite the well-demonstrated stimulatory role of prolactin (PRL) on breast cancer cell growth and the possible existence of a PRL-dependency in estrogen-independent mammary tumors, the therapeutic role of the antiprolactinemic drugs in the treatment of human breast cancer has still to be investigated and defined. Previous preliminary studies have already shown that the concomitant administration of antiprolactinemic agents may enhance the efficacy of cancer chemotherapy for breast carcinoma, whereas their impact on the efficacy of the endocrine therapy is still unknown. At present, the classic endocrine therapy for breast cancer consists of anti-estrogens plus LHRH-analogue. The concomitant administration of antiprolactinemic drugs could enhance the efficacy of treatment by blocking not only the action of estrogens, but also that of another growth factor for breast cancer, such as PRL. The present phase II study was performed to evaluate the efficacy and tolerability of a polyneuroendocrine approach for breast cancer, consisting of LHRH-analogue plus the anti-estrogen tamoxifen plus a long-acting antiprolactinemic agent, cabergoline. The study included 14 consecutive metastatic breast cancer women, heavily pretreated with the standard anticancer therapies and for whom no other conventional treatment was available. The LHRH-analogue, triptorelin, was given intramuscularly at a dose of 3.75 mg every 28 days, tamoxifen was given orally at 20 mg/day and cabergoline was given orally at 0.5 mg once/week. The clinical response consisted of partial response (PR) in 4 out of 14 (29%) patients, including one who had progressed on a previous treatment with triptorelin plus tamoxifen alone. A stable disease (SD) was achieved in another 5 patients, whereas the other 5 patients had a progressive disease (PD). Mean serum levels of PRL significantly decreased on treatment within the first month of therapy, and its decline was significantly more evident in patients with PR or SD than in those with PD. The treatment was well-tolerated in all patients, and in particular no cabergoline-related toxicity occurred. This preliminary study would suggest that the association of the long-acting antiprolactinemic drug cabergoline may further enhance the efficacy of the classical endocrine therapy for advanced breast cancer with anti-estrogens plus LHRH-analogues.

Antiprolactinemic approach in the treatment of metastatic breast cancer: a phase II study of polyneuroendocrine therapy with LHRH-analogue, tamoxifen and the long-acting antiprolactinemic drug cabergoline.

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Antiprolactinemic approach in the treatment of metastatic breast cancer: a phase II study of polyneuroendocrine therapy with LHRH-analogue, tamoxifen and the long-acting antiprolactinemic drug cabergoline.