Long-term Administration Of Tamoxifen Research Articles

Protective role of olive oil extract of propolis on short and long-term administration of tamoxifen in rats.

Tamoxifen (TAM) is an antiestrogenic agent used for adjuvant treatment in estrogen receptor-positive breast cancers in the pre/post-menopausal period. This study, it was aimed to determine the effect of olive oil extract of propolis (OEP) on short and long-term administration of TAM in rats. Wistar albino rats were divided into groups with eight animals in each. Groups: control, OEP, TAM, and OEP + TAM. At the end of the experiment, oxidative stress tests were performed with Enzyme-Linked ImmunoSorbent Assay (ELISA)on blood and tissue samples (liver, kidney, and ovary) taken from rats. After single-dose TAM administration, there was a significant increase in red blood cell, hematocrit, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration levels compared to the control group, a decrease in low-density lipoprotein (LDL) value, a significant increase in liver enzymes and fasting glucose values was detected compared with the control and propolis groups. A normalizing effect was observed in the group given OEP and TAM combined. The increase in Malondialdehyde (MDA) and the decrease in enzyme activities in tissues are also noteworthy. Propolis application reduced the tissue damage caused by TAM. In addition, improved cytokine levels, which increased with TAM administration. It has been concluded that OEP can be given in supportive treatment, as it improves hematological and antioxidant parameters in TAM treatment.

RSK-Mediated Non-canonical Activation of EphA2 by Tamoxifen.

The long-term administration of tamoxifen to estrogen receptor α (ERα)-positive breast cancer patients is an established treatment that reduces mortality and recurrence. However, resistance to tamoxifen and an increased risk of endometrial cancer may occur; therefore, the mechanisms by which tamoxifen causes these adverse effects warrant further study. Tamoxifen has been shown to activate mitogen-activated protein kinase (MAPK) in an ERα-independent manner; therefore, we investigated its effects on the MAPK-mediated non-canonical activation of EphA2, a critical event regulating cell migration. Tamoxifen at slightly higher concentrations induced the rapid phosphorylation of EphA2 at Ser-897 via the MAPK/extracellular signal-regulated kinase (ERK) kinase (MEK)-ERK-ribosomal S6 kinases (RSK) pathway in HeLa cells. In addition, tamoxifen significantly enhanced the migration ability of ERα-negative MDA-MB-231 breast cancer cells in RSK- and EphA2-dependent manners. Phosphorylated EphA2 was internalized and re-localized to the plasma membrane, including lamellipodia, in an RSK-dependent manner. Collectively, the present results provide novel insights into the tumor-promoting activity of tamoxifen.

DNA Adduct Assessment During Antihormonal Treatment of Perianal Gland Tumors With Tamoxifen in Male Dogs.

Determination of DNA adduct count was performed in mononuclear cells during antihormonal treatment of perianal gland tumors. Eight- to fifteen-year-old dogs with carcinoma (CAR Group; N=5), epithelioma (EPI Group; N=16) or adenoma (ADE Group; N=24) were used. The control group suffered from perineal hernia or rectal diverticulum (CTR Group; N=25). Blood was collected at baseline, and at one and six months after the beginning of the anti-hormonal treatment with tamoxifen (1 mg/kg of body weight). DNA adduct count was determined using autoradiography. At baseline, DNA adduct count reached the highest value in the CTR Group, and the lowest in the EPI Group (p<0.05). Six-month-long therapy with tamoxifen resulted in a significant increase in the DNA adduct count by 78.7%, 221.5% and 198.3% in the ADE, EPI and CAR groups, respectively (p<0.05). Increased DNA adduct formation after long-term administration of tamoxifen shows its genotoxicity.

Olig2-Lineage Astrocytes: A Distinct Subtype of Astrocytes That Differs from GFAP Astrocytes.

Astrocytes are the most abundant glia cell type in the central nervous system (CNS), and are known to constitute heterogeneous populations that differ in their morphology, gene expression and function. Although glial fibrillary acidic protein (GFAP) is the cardinal cytological marker of CNS astrocytes, GFAP-negative astrocytes can easily be found in the adult CNS. Astrocytes are also allocated to spatially distinct regional domains during development. This regional heterogeneity suggests that they help to coordinate post-natal neural circuit formation and thereby to regulate eventual neuronal activity. Here, during lineage-tracing studies of cells expressing Olig2 using Olig2CreER; Rosa-CAG-LSL-eNpHR3.0-EYFP transgenic mice, we found Olig2-lineage mature astrocytes in the adult forebrain. Long-term administration of tamoxifen resulted in sufficient recombinant induction, and Olig2-lineage cells were found to be preferentially clustered in some adult brain nuclei. We then made distribution map of Olig2-lineage astrocytes in the adult mouse brain, and further compared the map with the distribution of GFAP-positive astrocytes visualized in GFAPCre; Rosa-CAG-LSL-eNpHR3.0-EYFP mice. Brain regions rich in Olig2-lineage astrocytes (e.g., basal forebrain, thalamic nuclei, and deep cerebellar nuclei) tended to lack GFAP-positive astrocytes, and vice versa. Even within a single brain nucleus, Olig2-lineage astrocytes and GFAP astrocytes frequently occupied mutually exclusive territories. These findings strongly suggest that there is a subpopulation of astrocytes (Olig2-lineage astrocytes) in the adult brain, and that it differs from GFAP-positive astrocytes in its distribution pattern and perhaps also in its function. Interestingly, the brain nuclei rich in Olig2-lineage astrocytes strongly expressed GABA-transporter 3 in astrocytes and vesicular GABA transporter in neurons, suggesting that Olig2-lineage astrocytes are involved in inhibitory neuronal transmission.

Metformin- A Promising Agent for Chemoprevention in BRCA1 Carriers

Women who carry germline mutations in the BRCA1 gene (BRCA1 carriers) have the highest individual lifetime risk for breast cancer (BCa) known [1-3], with 50% of carriers developing breast cancer by age 50. BRCA2 carriers also have a higher risk but relatively lower than BRCA1 carriers. Currently available options for both BRCA1 and BRCA2 carriers include high-risk surveillance, risk reducing mastectomy or chemoprevention with the ant-estrogens Tamoxifen (TAM) and Raloxifene. Chemoprevention has been controversial in that BRCA1 carriers tend to make estrogen receptor negative tumors. Selective estrogen receptor modulators (SERMs) such as tamoxifen and raloxifene reduce the risk of estrogen receptor positive breast cancers. For example, results from the National Surgical Adjuvant Breast and Bowel Project (NSABP1) Tamoxifen chemoprevention study suggested that TAM is not effective in carriers of a BRCA1 mutation [4]. Regardless, there is conflicting evidence on this point and both TAM and Raloxifene are offered to BRCA1 carriers as well as BRCA2 carriers [5]. As a chemoprotective agent in the general population, Raloxifene shows a similar reduction in risk for invasive breast cancer to TAM, but not for in situ cancers, which comprise >20% of newly diagnosed cases; the incidence of noninvasive breast cancer is approximately 40% lower for women on TAM compared with Raloxifene [6,7]. Both TAM and Raloxifene are effective only against estrogen receptor-positive tumors [8], and Raloxifene is typically only prescribed in women who are postmenopausal and have decreased bone density [9]. Both drugs increase risk for serious side effects, including venous thrombosis and pulmonary embolism [10,11]. TAM is also associated with an increased risk for endometrial cancer and stroke [12-14]. Other side effects of both drugs include dyspareunia, cataracts, musculoskeletal complaints including leg cramps, weight gain, hot flashes, vaginal discharge, bone loss in premenopausal women and bladder control problems [15]. More recently, long-term administration of TAM was observed to cause hepatic tumors in rats, induced via a genotoxic mechanism [16]. Compounding the unfavorable side affect profile studies have determined that approximately 5 – 10% of the population carries a homozygous variant of the CYP2D6 gene that imparts low activity to convert TAM from its less active form to its active metabolite [17]. This research led the FDA to require a change in the labeling of Tamoxifen to include this information [18]. Concerns about the risk: benefit ratio have thus limited the use of TAM for prevention. Recent evidence suggests that only approximately 8.4% of BRCA carriers who have not undergone prophylactic mastectomy and are eligible to take Tamoxifen or Raloxifene [19], for risk reduction do so [20]. Certainly, there is an urgent need to identify other agents for breast cancer prevention in this high-risk group. In fact, data from our own Inherited Cancer Registry (ICARE) at Moffitt indicated that of 253 female BRCA1 and BRCA2 mutation carriers, 127 had remaining at risk breast tissue (including 40 with a prior breast cancer diagnosis). Of these women, 18.1% indicated that they had taken either TAM or Raloxifene (including 7/60 (11.7%) of BRCA1 carriers and 16/67 (23.9%) of BRCA2 carriers. Consequently, the poor uptake of existing breast cancer prevention options, which appears to be more marked in those with BRCA1 compared to BRCA2, serves to illustrate the urgent need to identify other agents for breast cancer prevention in this high-risk group.

A New Safer and More Effective Triphenylethylene Antiestrogen (SS1020) for the Treatment and Prevention of Breast Cancer.

Abstract Background: Tamoxifen (TAM) is widely used as a first-line endocrine therapy for breast cancer patients and as a prophylactic agent for women at high risk of developing this disease. Besides the significant benefit, long-term administration of TAM has serious side effects, including endometrial cancer. These side-effects are due to the DNA damaging and/or estrogenic action of the drug. Raloxifene (RAL) approved as a chemopreventive agent for postmenopausal women at high risk for invasive breast cancer retains an estrogenic action. RAL has a poor bioavailability. This makes it difficult to achieve adequate bioavailability by oral administration in humans. High doses are required to obtain an efficacy quivalent to that achieved with TAM. Several other antiestrogens were dropped out from the clinical trials due to their undesirable effects on the uterus. Therefore, development of new antiestrogen alternatives, but free of genotoxic and estrogenic potential, having significant antitumor potential beyond TAM and RAL is urgently required for breast cancer therapy and prevention.Results: SS1020 was developed as a new triphenylethylene antiestrogen in our laboratory. Although TAM is a hepatic carcinogen and produces a high level of DNA damage in rats, SS1020 did not produce such DNA damage. Unlike TAM and RAL, SS1020 had no detectable uterotrophic activity in OVX-rats even treated with a high dose (10 mg/kg). These indicate that SS1020 is free of genotoxic and estrogenic activities. The antitumor potential of SS1020 against 7,12-dimethyl-benz(a)anthracene (DMBA)-induced mammary carcinoma in rats and human MCF-7 breast cancer xenograft in athymic nude mice was superior to that of TAM and RAL. In addition, the development of estrogen-induced mammary tumor in rats was completed inhibited by dietary intake of SS1020, indicating that this compound has preventive potential. The bioavailability of SS1020 was approximately 35 times higher than that of RAL. The maximum blood concentration (493 ng/ml serum) of SS1020 was observed at 2 hour after the oral treatment while that of RAL (15.6 ng/ml) was at 6 hours, indicating that SS1020 is absorbed rapidly into the body. SS1020 has a much higher bioavailability than RAL, endowing it with higher antitumor potential than RAL.Conclusion: Taken together, SS1020 lacking genotoxic and estrogenic actions has anti-breast cancer activity superior to that of TAM and RAL and has a preventive potential. SS1020 is a safer and more effective antiestrogen candidate for breast cancer therapy and prevention. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4085.

Involvement of maternal embryonic leucine zipper kinase (MELK) in mammary carcinogenesis through interaction with Bcl-G, a pro-apoptotic member of the Bcl-2 family

IntroductionCancer therapies directed at specific molecular targets in signaling pathways of cancer cells, such as tamoxifen, aromatase inhibitors and trastuzumab, have proven useful for treatment of advanced breast cancers. However, increased risk of endometrial cancer with long-term tamoxifen administration and of bone fracture due to osteoporosis in postmenopausal women undergoing aromatase inhibitor therapy are recognized side effects. These side effects as well as drug resistance make it necessary to search for novel molecular targets for drugs on the basis of well-characterized mechanisms of action.MethodsUsing accurate genome-wide expression profiles of breast cancers, we found maternal embryonic leucine-zipper kinase (MELK) to be significantly overexpressed in the great majority of breast cancer cells. To assess whether MELK has a role in mammary carcinogenesis, we knocked down the expression of endogenous MELK in breast cancer cell lines using mammalian vector-based RNA interference. Furthermore, we identified a long isoform of Bcl-G (Bcl-GL), a pro-apoptotic member of the Bcl-2 family, as a possible substrate for MELK by pull-down assay with recombinant wild-type and kinase-dead MELK. Finally, we performed TUNEL assays and FACS analysis, measuring proportions of apoptotic cells, to investigate whether MELK is involved in the apoptosis cascade through the Bcl-GL-related pathway.ResultsNorthern blot analyses on multiple human tissues and cancer cell lines demonstrated that MELK was overexpressed at a significantly high level in a great majority of breast cancers and cell lines, but was not expressed in normal vital organs (heart, liver, lung and kidney). Suppression of MELK expression by small interfering RNA significantly inhibited growth of human breast cancer cells. We also found that MELK physically interacted with Bcl-GL through its amino-terminal region. Immunocomplex kinase assay showed that Bcl-GL was specifically phosphorylated by MELK in vitro. TUNEL assays and FACS analysis revealed that overexpression of wild-type MELK suppressed Bcl-GL-induced apoptosis, while that of D150A-MELK did not.ConclusionOur findings suggest that the kinase activity of MELK is likely to affect mammary carcinogenesis through inhibition of the pro-apoptotic function of Bcl-GL. The kinase activity of MELK could be a promising molecular target for development of therapy for patients with breast cancers.

Estrogen receptor polymorphisms in tamoxifen-treated women with breast cancer

In postmenopausal women with estrogen receptor (ER)-positive breast cancer, long-term tamoxifen administration has proved beneficial after surgical treatment and subsequent chemotherapy. One of the major adverse effects of tamoxifen is the development of endometrial pathology (polyps, endometrial hyperplasia and endometrial cancer). PvuII and XbaI polymorphisms of the estrogen receptor-α gene (ERα) and RsaI and AluI polymorphisms of the estrogen receptor-β gene (ERβ) have been associated with breast cancer. Thus the present study aimed to identify whether ER gene polymorphisms are associated with breast cancer stage or endometrial responsiveness to long-term tamoxifen treatment in 87 postmenopausal, tamoxifen-treated women with ER-positive breast cancer. The mean age of the patients was 58.7 ± 4.7 years and the mean duration of tamoxifen treatment was 3.9 ± 1.1 years. At diagnosis, the stage of breast cancer was determined as follows: 29 women (32%) at Stage I, 49 (58%) at Stage II and 9 (10%) at Stage III. The frequency distributions of the estrogen receptor polymorphisms in all women with breast cancer were not different from those predicted by the Hardy-Weinberg equilibrium hypothesis (p > 0.10). None of the ER polymorphisms studied was linked to either the presence of endometrial pathology or the stage of breast cancer.

Additional effect of SERM: mammary gland

One of selective estrogen receptor modulators (SERMs), tamoxifen, has been widely used for prevention of breast cancer, postoperative adjuvant therapy and treatment of advanced breast cancer. The relation of a long-term administration of tamoxifen and its adverse effects have been extensively investigated. Favorable effects of tamoxifen are:the reduction in the risk of contralateral breast cancer, gain in bone density in postmenopausal women and decrease in serum low-density lipoprotein cholesterol. Unfavorable effects are: gynecologic problems and the increase in the risk of endometrial cancer and thromboembolism. In contrast, another SERM, raloxifene, has reported to have similar favorable adverse effects but no unfavorable effect on endometrium.

Chemoprevention of Breast Cancer by Tamoxifen: Risks and Opportunities

ABSTRACTThe antiestrogen tamoxifen is widely used in the adjuvant therapy of breast cancers in women and helps to prevent the occurrence of breast tumors in healthy women. However, epidemiological studies have shown tamoxifen treatment to be associated with a 2- to 5-fold increased risk of endometrial cancer. In rats but not in mice, long-term administration of tamoxifen results in an increase in hepatocellular carcinomas. Mechanistically, this occurs through metabolic activation of the drug, mainly by the CYP3A family, to an electrophilic species, that causes DNA damage in target tissues, and subsequently leads to gene mutations. It is controversial whether low levels of DNA damage occur in human uterine tissues, and there is no evidence that this can be causally related to the mechanisms of carcinogenesis. In healthy women, the risk:benefits for the use of tamoxifen is in part related to the risk of developing breast cancer. The results from the carcinogenicity studies in rats do not predict the likelihood that women will develop liver cancer or indeed cancers in other organs. The mechanism of endometrial cancer in women remains unresolved, but the experience with tamoxifen has highlighted the potential problems that need to be addressed in the assessment of future generations of selective estrogen receptor modulators.

Changes in serum estrogen levels in women during tamoxifen therapy

Tamoxifen is considered an antiestrogen against breast cancer, yet it has known estrogenic side effects. We hypothesized that long-term administration of tamoxifen may significantly increase circulating estrogen levels in women with breast cancer. Serum dehydroepiandrosterone (DHEA), estrone (E1), and estradiol (E2) levels were prospectively measured in 47 breast cancer patients before and during tamoxifen therapy for 2 years. Differences in baseline and peak hormone levels during treatment were compared, and significance was determined by paired Student's t test. Mean DHEA levels increased by 133% from 61 mg/L to 142 mg/L (P <0.001) and mean E2 levels increased by 239% from 28 pg/mL to 95 pg/mL (P <0.05). Mean E1 levels increased by 264% from 42 pg/mL to 153 pg/mL (P = 0.06). Long-term tamoxifen therapy can be associated with increased serum levels of DHEA, E1, and E2. Elevated serum estrogens may explain tamoxifen's estrogenic effects and may represent a mechanism for the development of drug resistance.

Tamoxifen Prevents Sulpiride-Induced Weight Gain in Female Rats

To evaluate its potential utility in counteracting neuroleptic-induced obesity, the effects of long-term administration of tamoxifen (TAM) on body weight (BW) and food intake (FI) of gonadally intact and sulpiride-treated (SUL) female rats were assessed. In addition, estradiol and prolactin serum levels were measured in rats treated with SUL, SUL plus TAM and SUL plus bromocriptine (BR). TAM, at doses of 10, 50 and 100 μg, significantly decreased BW gain; FI was significantly reduced at the doses of 50 and 100 μg. In addition, doses of TAM ranging from 5-100 μg completely prevented SUL-induced BW gain and hyperphagia. BR also prevented SUL effects on BW and FI. In contrast to BR, concomitant administration of TAM did not prevent SUL-induced hyperprolactinemia. Estradiol levels were not modified by SUL alone or SUL plus BR, but they were significantly increased in the animals treated with TAM plus SUL. Neuroleptic-induced obesity in female rats might be related to an alteration in gonadal steroid balance secondary to hyperprolactinemia. While BR might counteract neuroleptic-induced weight gain by preventing hyperprolactinemia, TAM might directly interact with estrogen receptors, or indirectly increase estradiol levels. The use of TAM in preventing neuroleptic-induced obesity in humans warrants further investigation.

Treatment of hepatocellular carcinoma with tamoxifen: A double-blind placebo-controlled trial in 120 patients

Background & Aims : The progression of hepatocellular carcinoma may be influenced by estrogens. This has offered the rationale for evaluating the therapeutic usefulness of estrogen-receptor blockers; it is being debated whether long-term tamoxifen administration improves survival in patients with this neoplasm. The aim of this study was to assess the efficacy of tamoxifen administration in the treatment of hepatocellular carcinoma. Methods : One hundred twenty patients with this neoplasm who were not suitable for surgery, ethanol injection, or transarterial embolization were included in a placebo-controlled trial and randomized to tamoxifen, 20 mg/day per os, (group A, n = 58) or placebo (group B, n = 62). Patients with terminal diseases were excluded. Results : Both groups were similar with regard to sex, age, liver function (Child-Pugh's score, 6.5 ± 1.4 vs. 6.4 ± 1.4), baseline performance status, and tumor stage. Tamoxifen had no antitumoral effect with no differences in the survival between groups (1- and 2-year actuarial rate: group A, 51% and 27%; and group B, 43% and 29%; P = 0.75), even when stratifying patients according to baseline status. Furthermore, there were no differences in the probability of disease progression ( P = 0.46) and baseline performance status maintenance ( P = 0.93) during follow-up. Conclusions : Tamoxifen has no efficacy in the treatment of patients with advanced hepatocellular carcinoma.

Interferon-β, Retinoids, and Tamoxifen in the Treatment of Metastatic Breast Cancer: A Phase II Study

Based on the additive or synergistic antiproliferative effect of interferon and tamoxifen on breast cancer cell lines and on preclinical and clinical data on retinoids alone and in combination with antiestrogen or interferon, we designed a pilot phase II study to test the toxicity of simultaneous administration of interferon-beta (IFN-beta), retinoids (R), and tamoxifen (TAM) and the efficacy of this combination as salvage therapy in a group of patients with metastatic breast cancer (MBC). A total of 49 stage IV breast cancer patients, 11 pretreated with hormones, 26 with chemotherapy, and 12 with both, received 30 mg TAM and two dose levels of IFN-beta and retinyl palmitate. Among 49 evaluable patients, 27 achieved a clinical response (55%; 95% CI 41-69%), 10 had stable disease (20%), and in 12 (25%) the disease progressed. Toxicity with both dose levels was moderate and mainly hepatic. Median response duration, not statistically different in estrogen receptor-positive and negative patients, was 31.4 months (range 4.9-67). Median overall survival was 19.2 months (range 2-69). We have shown that long-term administration of TAM, IFN-beta, and retinyl palmitate is feasible with moderate toxicity. We have also demonstrated that this regimen is active in pretreated MBC patients and that responses are not influenced by receptor status.

PCNA-Immunoreactivity in the uterus of rats after treatment with the antiestrogen Tamoxifen

We used an antibody to the proliferating cell nuclear antigen (PCNA) to investigate the effect of the long-term administration of tamoxifen on proliferative activity in the uterus of mature rats. Untreated cycling and ovariectomized rats served as controls. The PCNA labelling indices (PI) and the mitotic indices (MI) were estimated for the luminal and glandular epithelium and for the stromal fibroblasts. A strong correlation was found for PI and MI in the luminal and in the glandular epithelium, and a lower, but also significant correlation, for the endometrial stroma cells. Tamoxifen treatment decreased the PI of the luminal epithelial cells and of the stroma as much as ovariectomy. In both of these groups, the proportion of anti-PCNA positive cells in the glandular epithelium was significantly higher than in the luminal epithelium. These data indicate that tamoxifen has a strong antiproliferative effect on the uterus of mature rats, and that this antiestrogenic action is cell type specific.

Does long-term administration of tamoxifen affect bone mineral density?

A retrospective study was performed to determine whether the long-term (5 years or more) administration of tamoxifen is detrimental to bone mineral density (BMD). 19 patients taking adjuvant tamoxifen for breast cancer were paired with 19 controls comparable in age, time since menopause and performance status. BMD was measured at the femoral neck, lumbar spine and total body by dual energy X-ray absorptiometry (DEXA). There was no detrimental effect on BMD at any site. There was a trend towards an increase in BMD at the femoral neck. There were minor decreases in the serum calcium, phosphate and alkaline phosphatase.

The effect of tamoxifen on the endometrium

Tamoxifen is one of the most important treatments for breast cancer, especially in postmenopausal patients. It acts primarily as an anti-estrogenic agent, due to its cytoplasmic estrogen receptor binding capacity. However, it also exerts a mild estrogenic effect. Since the prolonged use of estrogen has been reported to increase the rate of benign and malignant changes in the endometrium, we evaluated whether there is a correlation between tamoxifen therapy and endometrial benign and malignant conditions. The study group comprised 95 patients with breast cancer who were treated with tamoxifen. No control group was examined. Patients underwent vaginal ultrasonography and endometrial biopsy in order to evaluate any changes in the endometrium occurring during tamoxifen therapy. Pathological changes were observed in 14 patients, 13 of whom were treated with tamoxifen for more than 12 months. Of these women, 3 were diagnosed with endometrial cancer, 3 had mild dysplasia, 3 had endometrial hyperplasia, and 4 had a benign endometrial polyp. Our findings indicate a significant correlation between long-term tamoxifen administration and endometrial proliferation. We therefore recommend that women treated with tamoxifen for more than 12 months have an annual vaginal ultrasonography and endometrial biopsy.

Endometrial Cancer: Biochemical and Clinical Correlates

Some endometrial cancers and endometrial adenocarcinoma cell lines show amplified expression of proto-oncogenes (fos, fms, myc, myb, neu, and erb-B) and augmented production of growth factors (colony-stimulating factor 1, epidermal growth factor, transforming growth factor-alpha, and transforming growth factor beta) and epidermal growth factor receptor. Oncogene expression, the presence of estrogen and progesterone receptors, and the fraction of cells in S phase are useful biochemical prognostic indicators of clinical outcome, and markers recognized by monoclonal antibodies are available for use in following the clinical course of the disease and responses to treatment. In vivo and in vitro studies on normal and neoplastic tissues are providing evidence of paracrine influences on epithelial cell proliferation. Long-term administration of tamoxifen as adjuvant therapy for breast cancer has recently been found to increase the risk for development of endometrial cancer.

Effects of Long-Term Administration of Tamoxifen on Steroid Metabolism in Prostatic Carcinoma Patients

Six patients with advanced prostatic carcinoma were treated with tamoxifen (2 X 20 mg daily) for up to 3 months before orchiectomy. Blood samples for gonadotropin, sex steroid, and prostate-specific acid phosphatase (PAP) determinations were taken before tamoxifen treatment, daily for 1 week, and at monthly intervals. Steroid concentrations in the testis tissue and spermatic vein blood were assayed from samples taken at orchiectomy. No consistent changes were observed during tamoxifen treatment, although there was a transient drop in the mean concentrations of LH on days 3 and 4 of treatment. The circulating concentrations of estradiol tended to be increased at 1, 2, and 3 months of treatment. The spermatic vein concentrations of testosterone and its precursors tended to be higher than those in nontreated prostatic carcinoma patients previously reported from this laboratory, indicating slight stimulation of testicular steroidogenesis. There were no changes in circulating levels of PAP and no improvement in clinical condition, indicating that long-term tamoxifen administration is not effective in the treatment of prostate carcinoma.

Effect of D,L-2-difluoromethylornithine and endocrine manipulation on the induction of mammary carcinogenesis by 1-methyl-1-nitrosourea.

The purpose of this investigation was to establish an efficient route and dose regime for the long-term administration of tamoxifen in the study of mammary tumorigenesis in the rat. The second objective of this work was to determine whether treatment with D,L-2-difluoromethylornithine (DFMO), a synthetic inhibitor of the enzyme ornithine decarboxylase, would reduce the occurrence of mammary cancers in tamoxifen-treated or ovariectomized rats. A total of 265 female Sprague-Dawley rats were assigned to one of two experimental protocols. All animals were injected with 50 mg 1-methyl-1-nitrosourea (MNU) per kg body wt at 50 days of age. In experiment 1, beginning 7 days after the injection of the carcinogen, animals were assigned to one of six groups which received either 0, 1 or 5 mg tamoxifen citrate per kg AIN-76A purified diet in addition to either no DFMO or a 0.125% w/v solution of DFMO as the drinking water. The experiment was terminated 180 days following carcinogen treatment. Treatment with tamoxifen resulted in a dose-dependent reduction in cancer incidence, and the number of cancers induced and significantly prolonged the median cancer-free time. This effect was also accompanied by a decrease in the rate of body weight gain. Treatment with DFMO delayed latency and reduced tumor number. DFMO in addition to tamoxifen (1 mg/kg diet) further prolonged latency. In experiment 2 each animal was assigned to one or four treatment groups when its first palpable mammary tumor was detected. At that time each was either ovariectomized or sham-operated. In addition, the rats were either provided no DFMO or a 0.5% w/v solution of DFMO as the drinking water. The study was terminated 35 weeks following carcinogen injection. Ovariectomy significantly inhibited the occurrence of additional mammary tumors. Ovariectomy plus DFMO was more effective than ovariectomy alone in reducing tumor number. Collectively, these observations indicate that suppression of polyamine biosynthesis via the systemic administration of DFMO inhibits the development of ovarian hormone insensitive mammary tumors.