Precision diagnostics in cancer: Predict, prevent, and personalize.

In the past two decades since the first sequencing of the human genome, clinical genomics has undergone a renaissance with the advent of next generation sequencing (NGS) technologies. Whole genome sequencing is now increasingly available in the clinical setting at a fraction of the cost of the human genome reference sequence, and with turnaround times as short as 7-10days. Clinical genetics-based management has become more tractable with improved payer reimbursement and increased availability of targeted therapies, especially in the oncology space. Precision diagnostics in cancer allow clinicians to assess a patient's risk of developing cancers, detect and classify tumors, predict prognoses, select targeted therapies when available, and monitor their patient's disease burden longitudinally. This approach ushers in a new era of predictive and preventive oncology care that can be personalized to the genetics of the individual patient, the patient's tumor, and their clinical presentation. Within oncology, there are global collaborative efforts including the International Cancer Genome Consortium (ICGC), Pan-Cancer Analysis of Whole Genomes (PCAWG) and The Cancer Genome Atlas (TCGA) that have archived thousands of cancer genomes. In collaboration with databases including but not limited to cancer cataloging variant association with disease risk (ClinVar and others) and drug responses (PharmGKB and others), the study of somatic and germline genomic variation provides a wealth of information on cancer development, evolution, heterogeneity, and treatment response. Although many challenges still exist for defining all possible actionable genomic variants, we have unprecedented opportunity to gain mechanistic and clinical insights into human neoplastic diseases.

DLL3 as an Emerging Target for the Treatment of Neuroendocrine Neoplasms.

INTRODUCTION: Neuroendocrine neoplasms (NEN) are heterogeneous malignancies that can arise at almost any anatomical site and are classified as biologically distinct well-differentiated neuroendocrine tumors (NET) and poorly differentiated neuroendocrine carcinomas (NEC). Current systemic therapies for advanced disease, including targeted therapies, chemotherapy, and immunotherapy, are associated with limited duration of response. New therapeutic targets are needed. One promising target is delta-like ligand 3 (DLL3), an inhibitory ligand of the Notch receptor whose overexpression on the surface of NEN is associated with tumorigenesis. METHODS: This article is a narrative review that highlights the role of DLL3 in NEN progression and prognosis, the potential for therapeutic targeting of DLL3, and ongoing studies of DLL3-targeting therapies. Classification, incidence, pathogenesis, and current management of NEN are reviewed to provide biological context and illustrate the unmet clinical needs. DISCUSSION: DLL3 is overexpressed in many NENs, implicated in tumor progression, and is typically associated with poor clinical outcomes, particularly in patients with NEC. Targeted therapies using DLL3 as a homing beacon for cytotoxic activity mediated via several different mechanisms (eg, antibody-drug conjugates, T-cell engager molecules, CAR-Ts) have shown promising clinical activity in small-cell lung cancer (SCLC). DLL3 may be a clinically actionable target across NEN. CONCLUSIONS: Current treatment options for NEN do not provide sustained responses. DLL3 is expressed on the cell surface of many NEN types and is associated with poor clinical outcomes. Initial clinical studies targeting DLL3 therapeutically in SCLC have been promising, and additional studies are expanding this approach to the broader group of NEN.

Epigenetic Regulation in Gastroenteropancreatic Neuroendocrine Tumors.

Gastroenteropancreatic neuroendocrine neoplasms are a rare, diverse group of neuroendocrine tumors that form in the pancreatic and gastrointestinal tract, and often present with side effects due to hormone hypersecretion. The pathogenesis of these tumors is known to be linked to several genetic disorders, but sporadic tumors occur due to dysregulation of additional genes that regulate proliferation and metastasis, but also the epigenome. Epigenetic regulation in these tumors includes DNA methylation, chromatin remodeling and regulation by noncoding RNAs. Several large studies demonstrate the identification of epigenetic signatures that may serve as biomarkers, and others identify innovative, epigenetics-based targets that utilize both pharmacological and theranostic approaches towards the development of new treatment approaches.

ISGylation is increased in the peripheral blood mononuclear cells derived from symptomatic COVID-19 patients.

Cytokine-driven hyper inflammation has been identified as a critical factor behind poor outcomes in patients severely infected with SARS-CoV-2 virus. Notably, protein ISGylation, a protein conjugated form of Type 1 IFN-inducible ubiquitin-like protein ISG15 (Interferon-Stimulated Gene 15), induces cytokine storm (CS) and augments colonic inflammation in colitis-associated colon cancers in mouse models. However, whether ISGylation is increased and causally responsible for CS and hyper inflammation in symptomatic COVID-19 patients is unknown. Here, we measured ISGylation levels in peripheral blood mononuclear cells (PBMCs) from 10 symptomatic (SARS-CoV-2-positive with symptoms) and asymptomatic (SARS-CoV-2-positive with no symptoms) COVID-19 patients, and 4 uninfected individuals (SARS-CoV-2-negative), using WesTm assay. Strikingly, we note significant increases in protein ISGylation and MX-1 (myxovirus-resistance protein-1) protein levels, both induced by type-I IFN, in symptomatic but not in asymptomatic patients and uninfected individuals. Knowing that ISGylation augments CS and intestinal inflammation in colon cancers, we propose that increased ISGylation may be an underlying cause of CS and inflammation in symptomatic patients.

ER+ Breast Cancer Mammosphere Formation and Analysis.

Mammosphere formation assays are a popular and convenient technique in the study of breast cancer by providing an in vitro mechanism by which to study breast cancer stem cell (BCSC) contribution to tumorigenesis, as well as more closely mimicking the three-dimensional tumor microenvironment. In these assays, BCSCs are stimulated to proliferate in low adherence tissue culture dishes and the resulting mammospheres exhibit activation of stem cell-related signaling pathways. Here we describe the process for generating and analyzing mammospheres under varying conditions.

Targeting Notch in oncology: the path forward.

Notch signalling is involved in many aspects of cancer biology, including angiogenesis, tumour immunity and the maintenance of cancer stem-like cells. In addition, Notch can function as an oncogene and a tumour suppressor in different cancers and in different cell populations within the same tumour. Despite promising preclinical results and early-phase clinical trials, the goal of developing safe, effective, tumour-selective Notch-targeting agents for clinical use remains elusive. However, our continually improving understanding of Notch signalling in specific cancers, individual cancer cases and different cell populations, as well as crosstalk between pathways, is aiding the discovery and development of novel investigational Notch-targeted therapeutics.

Breast Cancer Stem Cells.

Breast cancer stem cells (BCSC) have been implicated in tumor initiation, progression, metastasis, recurrence, and resistance to therapy. The origins of BCSCs remain controversial due to tumor heterogeneity and the presence of such small side populations for study, but nonetheless, cell surface markers and their correlation with BCSC functionality continue to be identified. BCSCs are driven by persistent activation of developmental pathways, such as Notch, Wnt, Hippo, and Hedgehog and new treatment strategies that are aimed at these pathways are in preclinical and clinical development.

Clinical and Preclinical Advances in Gastroenteropancreatic Neuroendocrine Tumor Therapy.

The molecular events leading to gastroenteropancreatic neuroendocrine tumor (GEP-NET) formation are largely unknown. Over the past decades, systemic chemotherapies have been replaced by therapies directed at particular molecular targets such as the somatostatin receptors, mTOR complexes or proangiogenic molecules. These approaches have demonstrated some success in subtypes of this heterogeneous tumor group, but responses are still widely varied. This review highlights the clinical trials ongoing for neuroendocrine tumors (NETs) and includes emerging immunotherapy, which holds great promise for NETs based on successes in other tumor types. Current avenues of preclinical research, including Notch and PI3K/AKT, will lead to additional targeted therapies based on genome-wide studies that have cast a wide net in the search for driver mutations. Future preclinical and clinical investigations are required to identify those mutations predictive of therapeutic response or disease progression. Results of current clinical trials outlined here will better inform patient management with respect to agent selection, timing, duration and combination therapy in the treatment of NETs.

Acquisition of an oncogenic fusion protein is sufficient to globally alter the landscape of miRNA expression to inhibit myogenic differentiation.

The differentiation status of tumors is used as a prognostic indicator, with tumors comprised of less differentiated cells exhibiting higher levels of aggressiveness that correlate with a poor prognosis. Although oncogenes contribute to blocking differentiation, it is not clear how they globally alter miRNA expression during differentiation to achieve this result. The pediatric sarcoma Alveolar Rhabdomyosarcoma, which is primarily characterized by the expression of the PAX3-FOXO1 oncogenic fusion protein, consists of undifferentiated muscle cells. However, it is unclear what role PAX3-FOXO1 plays in promoting the undifferentiated state. We demonstrate that expression of PAX3-FOXO1 globally alters the expression of over 80 individual miRNA during early myogenic differentiation, resulting in three primary effects: 1) inhibition of the expression of 51 miRNA essential for promoting myogenesis, 2) promoting the aberrant expression of 43 miRNA not normally expressed during myogenesis, and 3) altering the expression pattern of 39 additional miRNA. Combined, these changes are predicted to have an overall negative effect on myogenic differentiation. This is one of the first studies describing how an oncogene globally alters miRNA expression to block differentiation and has clinical implications for the development of much needed multi-faceted tumor-specific therapeutic regimens.

Acquisition of an oncogenic fusion protein serves as an initial driving mutation by inducing aneuploidy and overriding proliferative defects.

While many solid tumors are defined by the presence of a particular oncogene, the role that this oncogene plays in driving transformation through the acquisition of aneuploidy and overcoming growth arrest are often not known. Further, although aneuploidy is present in many solid tumors, it is not clear whether it is the cause or effect of malignant transformation. The childhood sarcoma, Alveolar Rhabdomyosarcoma (ARMS), is primarily defined by the t(2;13)(q35;q14) translocation, creating the PAX3-FOXO1 fusion protein. It is unclear what role PAX3-FOXO1 plays in the initial stages of tumor development through the acquisition and persistence of aneuploidy. In this study we demonstrate that PAX3-FOXO1 serves as a driver mutation to initiate a cascade of mRNA and miRNA changes that ultimately reprogram proliferating myoblasts to induce the formation of ARMS. We present evidence that cells containing PAX3-FOXO1 have changes in the expression of mRNA and miRNA essential for maintaining proper chromosome number and structure thereby promoting aneuploidy. Further, we demonstrate that the presence of PAX3-FOXO1 alters the expression of growth factor related mRNA and miRNA, thereby overriding aneuploid-dependent growth arrest. Finally, we present evidence that phosphorylation of PAX3-FOXO1 contributes to these changes. This is one of the first studies describing how an oncogene and post-translational modifications drive the development of a tumor through the acquisition and persistence of aneuploidy. This mechanism has implications for other solid tumors where large-scale genomics studies may elucidate how global alterations contribute to tumor phenotypes allowing the development of much needed multi-faceted tumor-specific therapeutic regimens.

Notch Signaling in Neuroendocrine Tumors.

Carcinoids and neuroendocrine tumors (NETs) are a heterogeneous group of tumors that arise from the neuroendocrine cells of the GI tract, endocrine pancreas, and the respiratory system. NETs remain significantly understudied with respect to molecular mechanisms of pathogenesis, particularly the role of cell fate signaling systems such as Notch. The abundance of literature on the Notch pathway is a testament to its complexity in different cellular environments. Notch receptors can function as oncogenes in some contexts and tumor suppressors in others. The genetic heterogeneity of NETs suggests that to fully understand the roles and the potential therapeutic implications of Notch signaling in NETs, a comprehensive analysis of Notch expression patterns and potential roles across all NET subtypes is required.

The Cell Death Inhibitor ARC Is Induced in a Tissue-Specific Manner by Deletion of the Tumor Suppressor Gene Men1, but Not Required for Tumor Development and Growth.

Multiple endocrine neoplasia type 1 (MEN1) is a genetic disorder characterized by tissue-specific tumors in the endocrine pancreas, parathyroid, and pituitary glands. Although tumor development in these tissues is dependent upon genetic inactivation of the tumor suppressor Men1, loss of both alleles of this gene is not sufficient to induce these cancers. Men1 encodes menin, a nuclear protein that influences transcription. A previous ChIP on chip analysis suggested that menin binds promoter sequences of nol3, encoding ARC, which is a cell death inhibitor that has been implicated in cancer pathogenesis. We hypothesized that ARC functions as a co-factor with Men1 loss to induce the tissue-restricted distribution of tumors seen in MEN1. Using mouse models that recapitulate this syndrome, we found that biallelic deletion of Men1 results in selective induction of ARC expression in tissues that develop tumors. Specifically, loss of Men1 in all cells of the pancreas resulted in marked increases in ARC mRNA and protein in the endocrine, but not exocrine, pancreas. Similarly, ARC expression increased in the parathyroid with inactivation of Men1 in that tissue. To test if ARC contributes to MEN1 tumor development in the endocrine pancreas, we generated mice that lacked none, one, or both copies of ARC in the context of Men1 deletion. Studies in a cohort of 126 mice demonstrated that, although mice lacking Men1 developed insulinomas as expected, elimination of ARC in this context did not significantly alter tumor load. Cellular rates of proliferation and death in these tumors were also not perturbed in the absence of ARC. These results indicate that ARC is upregulated by loss Men1 in the tissue-restricted distribution of MEN1 tumors, but that ARC is not required for tumor development in this syndrome.

miR-24 regulates menin in the endocrine pancreas.

Menin, the product of the MEN1 gene, functions as a tumor suppressor and was first identified in 1997 due to its causative role in the endocrine tumor disorder multiple endocrine neoplasia, type 1 (MEN1). More recently, menin has been identified as a key player in pancreatic islet biology with the observation of an inverse relationship between menin levels and pancreatic islet proliferation. However, the factors regulating menin and the MEN1 gene in the pancreas are poorly understood. Here, we describe the regulation of menin by miR-24 and demonstrate that miR-24 directly decreases menin levels and impacts downstream cell cycle inhibitors in MIN6 insulinoma cells and in ßlox5 immortalized ß-cells. This regulation of menin impacts cell viability and proliferation in ßlox5 cells. Furthermore, our data show a feedback regulation between miR-24 and menin that is present in the pancreas, suggesting that miR-24 regulates menin levels in the pancreatic islet.

A mouse model of androgenetic alopecia.

Androgenetic alopecia (AGA), commonly known as male pattern baldness, is a form of hair loss that occurs in both males and females. Although the exact cause of AGA is not known, it is associated with genetic predisposition through traits related to androgen synthesis/metabolism and androgen signaling mediated by the androgen receptor (AR). Current therapies for AGA show limited efficacy and are often associated with undesirable side effects. A major hurdle to developing new therapies for AGA is the lack of small animal models to support drug discovery research. Here, we report the first rodent model of AGA. Previous work demonstrating that the interaction between androgen-bound AR and beta-catenin can inhibit Wnt signaling led us to test the hypothesis that expression of AR in hair follicle cells could interfere with hair growth in an androgen-dependent manner. Transgenic mice overexpressing human AR in the skin under control of the keratin 5 promoter were generated. Keratin 5-human AR transgenic mice exposed to high levels of 5alpha-dihydrotestosterone showed delayed hair regeneration, mimicking the AGA scalp. This effect is AR mediated, because treatment with the AR antagonist hydroxyflutamide inhibited the effect of dihydrotestosterone on hair growth. These results support the hypothesis that androgen-mediated hair loss is AR dependent and suggest that AR and beta-catenin mediate this effect. These mice can now be used to test new therapeutic agents for the treatment of AGA, accelerating the drug discovery process.

Loss of inhibitory insulin receptor substrate-1 phosphorylation is an early event in mammalian target of rapamycin-dependent endometrial hyperplasia and carcinoma.

Insulin-like growth factor-I receptor signaling contributes to the development of endometrial hyperplasia, the precursor to endometrioid-type endometrial carcinoma, in humans and in rodent models. This pathway is under both positive and negative regulation, including S6 kinase (S6K) phosphorylation of insulin receptor substrate-1 (IRS-1) at S636/639, which occurs downstream of mammalian target of rapamycin (mTOR) activation to inhibit this adapter protein. We observed activation of mTOR with a high frequency in human endometrial hyperplasia and carcinoma, but an absence of IRS-1 phosphorylation, despite high levels of activated S6K. To explore when during disease progression mammalian target of rapamycin (mTOR) activation and loss of negative feedback to IRS-1 occurred, we used the Eker rat (Tsc2(Ek/+)) model, where endometrial hyperplasia develops as a result of loss of Tsc2, a "gatekeeper" for mTOR. We observed mTOR activation early in progression in hyperplasias and in some histologically normal epithelial cells, suggesting that event(s) in addition to loss of Tsc2 were required for progression to hyperplasia. In contrast, whereas IRS-1 S636/639 phosphorylation was observed in normal epithelium, it was absent from all hyperplasias, indicating loss of IRS-1 inhibition by S6K occurred during progression to hyperplasia. Treatment with a mTOR inhibitor (WAY-129327) significantly decreased hyperplasia incidence and proliferative indices. Because progression from normal epithelium to carcinoma proceeds through endometrial hyperplasia, these data suggest a progression sequence where activation of mTOR is followed by loss of negative feedback to IRS-1 during the initial stages of development of this disease.

Comparison of human and rat uterine leiomyomata: identification of a dysregulated mammalian target of rapamycin pathway.

Uterine leiomyomata, or fibroids, are benign tumors of the uterine myometrium that significantly affect up to 30% of reproductive-age women. Despite being the primary cause of hysterectomy in the United States, accounting for up to 200,000 procedures annually, the etiology of leiomyoma remains largely unknown. As a basis for understanding leiomyoma pathogenesis and identifying targets for pharmacotherapy, we conducted transcriptional profiling of leiomyoma and unaffected myometrium from humans and Eker rats, the best characterized preclinical model of leiomyomata. A global comparison of mRNA from leiomyoma versus myometrium in human and rat identified a highly significant overlap of dysregulated gene expression in leiomyomata. An unbiased pathway analysis using a method of gene-set enrichment based on the sigPathway algorithm detected the mammalian target of rapamycin (mTOR) pathway as one of the most highly up-regulated pathways in both human and rat tumors. To validate this pathway as a therapeutic target for uterine leiomyomata, preclinical studies were conducted in Eker rats. These rats develop uterine leiomyomata as a consequence of loss of Tsc2 function and up-regulation of mTOR signaling. Inhibition of mTOR in female Eker rats with the rapamycin analogue WAY-129327 for 2 weeks decreased mTOR signaling and cell proliferation in tumors, and treatment for 4 months significantly decreased tumor incidence, multiplicity, and size. These results identify dysregulated mTOR signaling as a component of leiomyoma etiology across species and directly show the dependence of uterine leiomyomata with activated mTOR on this signaling pathway for growth.

Effects of various selective estrogen receptor modulators with or without conjugated estrogens on mouse mammary gland.

Selective estrogen receptor modulators (SERMs) are small molecules that, depending on the end point measured, may either function as estrogen receptor (ER) agonists or antagonize estrogens' agonist activity. A key feature of SERMs is the inhibition of ER agonist action on the uterus and mammary gland, but the degree of antagonism varies among compounds and end points. Bazedoxifene is a SERM that is being clinically evaluated both as a monotherapy for the prevention and treatment of osteoporosis and in combination with conjugated estrogens (CEs) for the treatment of menopausal symptoms and prevention of osteoporosis. The studies reported here compare the relative ER agonist and antagonist effects of three pharmacologically distinct SERMs (bazedoxifene, raloxifene, and lasofoxifene) on the ovariectomized mouse when administered alone or as a tissue-selective estrogen complex, a term used to describe the partnering of a SERM and one or more estrogens. At the minimum dose required to maximally reduce CE-stimulated uterine wet weight increase for each SERM, the degree of inhibition varied among the SERMs, with a rank order of bazedoxifene approximately raloxifene > lasofoxifene, in which only bazedoxifene was statistically similar to vehicle. In the mammary gland, in which amphiregulin mRNA and morphological effects were measured, bazedoxifene generally exhibited less agonist activity and was a more effective antagonist of CE than raloxifene or lasofoxifene. In summary, in an animal model evaluating estrogen-modulated uterine effects and mammary gland development, bazedoxifene exhibited less ER agonist activity than raloxifene or lasofoxifene, and, as a tissue-selective estrogen complex, bazedoxifene/CE demonstrated less mammary gland stimulation than raloxifene/CE and lasofoxifene/CE.

Activity of three selective estrogen receptor modulators on hormone-dependent responses in the mouse uterus and mammary gland.

Selective estrogen receptor modulators (SERMs) have the unique potential to provide estrogenic effects in the skeletal and cardiovascular system, while minimizing/eliminating side effects on reproductive organs. However, despite the unifying characteristic of mixed estrogen receptor (ER) agonist/antagonist activity, compounds within this class are not interchangeable. In order to define and compare the effects of SERMs on different hormone-responsive tissues, we evaluated effects of bazedoxifene acetate (BZA), lasofoxifene (LAS) and raloxifene (RAL) in the mammary gland and uterus of the ovariectomized mouse. Endpoints measured included those regulated by estradiol alone (uterine wet weight, uterine G protein-coupled receptor 105 (GPR105) mRNA expression and mammary gland indoleamine-pyrrole 2,3 dioxygenase (INDO) mRNA expression) as well as others that required the combination of estradiol and progesterone (uterine serine protease inhibitor Kazal type 3 (Spink3) mRNA expression, mammary gland morphology and mammary gland defensin beta1 (Defbeta1) mRNA expression). The three SERMs tested had variable agonist and antagonist activity on these endpoints. In the uterus, the SERMs were mixed agonists/antagonists on estradiol-induced wet weight increase, whereas all three SERMs were estrogen receptor antagonists on GPR105 mRNA expression. However, in the presence of progesterone, BZA and RAL were agonists on Spink3 expression, while LAS was primarily an antagonist. In the mammary gland, BZA and RAL were predominantly agonists on the endpoint of mammary morphology and all three SERMs were clear agonists on Defbeta1 mRNA expression, an E+P-dependent marker. Finally, LAS and RAL had mixed agonist/antagonist activity on INDO mRNA expression, while BZA had only antagonist activity. These results demonstrate that compounds with small structural differences can elicit distinct biological responses, and that in general, SERMs tended to behave more as antagonists on endpoints requiring estrogen alone and agonists on endpoints requiring the combination of estrogen and progesterone.

A study of 17beta-estradiol-regulated genes in the vagina of postmenopausal women with vaginal atrophy.

BACKGROUND: Vaginal atrophy (VA) is a prevalent disorder in postmenopausal women that is characterized by decreased epithelial thickness, reduced vaginal maturation index (VMI) and increased vaginal pH. Current medical therapy consists of local or systemic replacement of estrogens. OBJECTIVE: The goal of this study was to understand, at a molecular level, the effect of estradiol (E2) on the vaginal epithelium. METHODS: Nineteen women were treated with E2 delivered through a skin patch at a dose of 0.05mg/day for 12 weeks. The diagnosis of VA was confirmed by a VMI with < or =5% superficial cells and vaginal pH>5.0. Vaginal biopsy samples were collected at baseline and after treatment. Differentially expressed mRNA transcripts in these biopsies were determined by microarray analysis. RESULTS: All 19 subjects had increased VMI (>5%) and/or reduced pH (< or =5) following treatment. Most subjects also had increased serum E2 levels and reduced serum FSH levels. Transcriptional profiling of vaginal biopsies identified over 3000 E2-regulated genes, including those involved in several key pathways known to regulate cell growth and proliferation, barrier function and pathogen defense. CONCLUSIONS: E2 controls a plethora of cellular pathways that are concordant with its profound effect on vaginal physiology. The data presented here are a useful step toward understanding the role of E2 in vaginal tissue and the development of novel therapeutics for the treatment of VA.

Development of a mouse model of mammary gland versus uterus tissue selectivity using estrogen- and progesterone-regulated gene markers.

We have identified mRNA markers of estradiol and progesterone action in the mouse mammary gland and uterus to establish an in vivo model for the evaluation of novel and potentially tissue selective estrogens and progestins. Gene chip analysis of mRNA from ovariectomized (OVX) mice treated with vehicle (V), 17beta-estradiol (E2), progesterone (P) or E2+P for 7 days identified defensinbeta1 (Defbeta1) and indoleamine-pyrrole 2,3 dioxygenase (INDO) as markers of E2 and P action in the mammary gland, and serine protease inhibitor, Kazal type 3 (Spink3) and G protein-coupled receptor 105 (GPR105) as markers in the uterus. Defbeta1 and Spink3 are both upregulated by E2+P, whereas INDO and GPR105 have a complementary profile of upregulation by E2 alone and suppression of the E2 effect by P. Quantitative RT-PCR analysis of mammary gland markers was concordant with histological changes. Using this model, medroxyprogesterone acetate (MPA) and tanaproget (TNPR), a novel nonsteroidal progesterone receptor agonist, were evaluated and found to have no marked tissue selectivity relative to progesterone. In addition, the ERalpha selective ligand propyl pyrazole triol (PPT) and the ERbeta selective ligands ERB-041 and WAY-202196 were evaluated on the mammary gland endpoints of histology and Defbeta1 mRNA expression, and showed that ERalpha stimulation is necessary and sufficient for eliciting estradiol-mediated changes in the mammary gland.