Inguinal Glands Research Articles

Abstract B2: Maternal consumption of canola oil reduces mammary gland cancer risk in C3(1) Tag offspring

Abstract B2 Maternal diet may influence development of the offspring and may influence future cancer risk. Maternal consumption of diet high in n-6 (omega 6) polyunsaturated fats has been shown to increase risk for mammary gland cancer (Hilakivi-Clarke et al, 1997). We wanted to know if the substitution of corn oil with canola oil in the maternal diet might reduce the risk for breast cancer. Such a change would decrease dietary n-6 fat and increase n-3 fat. A study was devised to determine whether exposure to a diet that has less omega 6 and more omega 3 FAs during gestation and lactation would reduce the risk for mammary cancer in female offspring. Female SV 129 mice were divided into two groups and placed on diets either containing 10% w/w corn oil (corn oil is 50% omega 6 and < 0.5% omega 3) or 10% w/w canola oil (canola oil is 20% omega 6 and 10% omega 3). After two weeks the females were bred with homozygous C31 Tag transgenic male mice. The transgenic mice bear a transgene for the SV40 large T antigen with a prostatic steroid binding protein promoter. The female progeny, hemizygous for the transgene, are the experimental mice for this study. On a standard diet, females would be expected to develop mammary gland cancer by 6 months of age. At weaning, female progeny from each litter were all maintained on the basal corn oil containing diet. The female hemizygous mice were euthanized at 3weeks, 110, 130, 150 and 170 days. Results showed that the total tumor weight, number of glands with tumor and fraction of mice with tumors were higher in progeny of mother fed a corn oil diet than in progeny of mother fed a canola oil diet. No significant difference in the body weight of progeny from corn oil and canola fed mothers. At weaning the lipid composition of the inguinal fat pad, mammary gland and liver shows a higher level of omega 3 fatty acids in the offspring of mice fed the high n-3 diet. Mammary gland gene expression assay performed on three weeks and 130 days old mice reveals up as well as down regulation in several genes in canola versus corn group. The up regulated genes include CCAAT-enhancer binding protein beta (CEBPβ), a transcription factor that is involved in mammary gland differentiation (550-fold at 130days) and Early growth response 1 (Egr1), a tumor suppressor gene (13-fold at 130days). Genes down regulated include Bcl2-like 1(Bcl2l1), an antiapoptotic gene (-2.03-fold at 3weeks) and Fatty acid synthase (Fas), an enzyme involved in fatty acid synthesis and active in cancer cells (-7.09 at 130days). Western blot analysis confirmed the differential gene expression of CEBPβ and Fas. Citation Information: Cancer Prev Res 2008;1(7 Suppl):B2.

99mTc‐LABELED DEXTRAN FOR MAMMARY LYMPHOSCINTIGRAPHY IN DOGS

Lymphoscintigraphy is the technique of choice for sentinel lymph node detection in women with early breast cancer, but there is limited information evaluating the value of this technique in animals. We investigated mammary lymphatic drainage in 25 young female mongrel dogs by intramammary injection of 18.5 MBq of 99mTc-dextran (70,000 Da). Lymph node anatomical referencing was obtained using an external marker, bone scintigraphy, or scintiscanning the body contour. Cranial and caudal thoracic mammary glands drained into the cranial sternal lymph node and axillary lymph center. The cranial thoracic mammary gland also drained into the superficial cervical lymph node in two of five animals. The cranial abdominal gland was drained by the axillary lymph center. The caudal abdominal mammary gland was drained by the superficial inguinal lymph node in all animals and simultaneously by medial iliac lymph nodes in four of five animals. In one dog, this mammary gland was also drained by the mediastinal and the superficial cervical lymph nodes. The inguinal mammary gland was drained by superficial inguinal lymph nodes and simultaneously via the medial iliac lymph node in one animal. Lymphatic communications between lymph nodes were identified in 11 of 25 (44%) animals. 99mTc-dextran mammary lymphoscintigraphy was easy and rapid to perform and may provide valuable information for further studies.

17β-Estradiol Mobilizes Bone Marrow–Derived Endothelial Progenitor Cells to Tumors

Neovascularization is critical for tumor growth and development. The cellular mediators for this process are yet to be defined. We discovered that bone marrow-derived endothelial progenitor cells (BM-EPC), having the phenotype (CD133+, CD34+, VEGFR-2+), initiate neovascularization in response to TG1-1 mammary cells implanted in the inguinal mammary gland of Tie-2 GFP transgenic mice. The fluorescence tag allowed for tracing the migration of green fluorescent protein-tagged endothelial progenitor cells to tumor tissues. We discovered that 17-beta estradiol supplementation of ovariectomized mice significantly enhanced BM-EPC-induced neovascularization and secretion of angiogenic factors within the tumor microenvironment. Cell-based system analyses showed that estrogen-stimulated BM-EPCs secreted paracrine factors which enhanced TG1-1 cell proliferation and migration. Furthermore, TG1-1 cell medium supplemented with estrogen-induced BM-EPC mediated tubulogenesis, which was an experimental in vivo representation of the neovasculature. Our data provide evidence of BM-EPC mammary tumor cell interactions and identify a novel cellular mediator of tumor progression that can be exploited clinically.

Histomorphometry and expression of CDC-47 and caspase-3 in mammary glands of pregnant female rats with artificial hyperthyroidism

The purpose of this study was to evaluate the effect of hyperthyroidism on mammary gland development and expression of two protein markers, CDC-47 for proliferation and caspase-3 for apoptosis in pregnant female rats. Thirty-six adult female Wistar rats were used in two groups: hyperthyroid and control. Rats were mated 60 days after the onset of thyroxine administration. Six animals/group were sacrificed on gestation days 7, 14, and 19. Artificial hyperthyroidism was induced by daily administration of thyroxine in the drinking water until the end of gestation. At the end of each period, rats were sacrificed, and their inguinal mammary glands were collected and processed for morphometric analysis. The percentages of epithelium, stroma, adipose tissue, and lacteal secretion were determined. Immunohistochemical analysis was also carried out using anti-CDC-47 and anti-caspase-3 antibodies to study proliferation and apoptosis, respectively. On the 19th day of gestation, thyroxine treatment significantly increased the percentage of mammary epithelium. Hyperthyroidism, however, did not change CDC-47 expression. The hyperthyroid group presented early lactogenesis and significantly larger lacteal secretion on the 19th day of gestation. There was no significant difference in caspase-3 expression between groups in any period. We may conclude that hyperthyroidism accelerates mammary gland development and increases lacteal secretion during gestation without increasing the proliferation rate and the expression of caspase-3.

Redescription of the tadpoles of three species of frogs from Uruguay (Amphibia: Anura: Leiuperidae and Leptodactylidae), with notes on natural history

In this work the tadpoles of the neotropical frogs Leptodactylus latinasus, Physalaemus biligonigerus and Physalaemus riograndensis are redescribed. Relevant features of L. latinasus tadpoles are a medial vent tube, labial tooth row formula (LTRF) 2(2)/3(1), and oral disc with a single row of marginal papillae interrupted by a dorsal gap, similarly to other species within the L. fuscus species group. Tadpoles of P. riograndensis have a medial vent tube, LTRF 2(2)/2(1), oral disc with single row of marginal papillae, interrupted by a dorsal gap and usually two ventrolateral gaps. The tadpole of P. biligonigerus has a dextral vent tube, the oral disc presents a single row of marginal papillae (sometimes double ventrally) with dorsal gap, and LTRF 2(2)/2(1). Although considered relevant for the taxonomy of Physalaemus, character variation of larval external morphology is incongruous with the phenetic species group arrangements proposed up to date. A reproductive mode previously unreported for P. riograndensis and P. henselii was observed: foam nests in the humid ground outside ponds. We also report the display of deimatic behavior in L. latinasus, L. ocellatus, P. henselii, and P. biligonigerus, in the last case with exhibition of the eye-like inguinal glands.

An oestrogen-dependent model of breast cancer created by transformation of normal human mammary epithelial cells

IntroductionAbout 70% of breast cancers express oestrogen receptor α (ESR1/ERα) and are oestrogen-dependent for growth. In contrast with the highly proliferative nature of ERα-positive tumour cells, ERα-positive cells in normal breast tissue rarely proliferate. Because ERα expression is rapidly lost when normal human mammary epithelial cells (HMECs) are grown in vitro, breast cancer models derived from HMECs are ERα-negative. Currently only tumour cell lines are available to model ERα-positive disease. To create an ERα-positive breast cancer model, we have forced normal HMECs derived from reduction mammoplasty tissue to express ERα in combination with other relevant breast cancer genes.MethodsCandidate genes were selected based on breast cancer microarray data and cloned into lentiviral vectors. Primary HMECs prepared from reduction mammoplasty tissue were infected with lentiviral particles. Infected HMECs were characterised by Western blotting, immunofluorescence microscopy, microarray analysis, growth curves, karyotyping and SNP chip analysis. The tumorigenicity of the modified HMECs was tested after orthotopic injection into the inguinal mammary glands of NOD/SCID mice. Cells were marked with a fluorescent protein to allow visualisation in the fat pad. The growth of the graft was analysed by fluorescence microscopy of the mammary glands and pathological analysis of stained tissue sections. Oestrogen dependence of tumour growth was assessed by treatment with the oestrogen antagonist fulvestrant.ResultsMicroarray analysis of ERα-positive tumours reveals that they commonly overexpress the Polycomb-group gene BMI1. Lentiviral transduction with ERα, BMI1, TERT and MYC allows primary HMECs to be expanded in vitro in an oestrogen-dependent manner. Orthotopic xenografting of these cells into the mammary glands of NOD/SCID mice results in the formation of ERα-positive tumours that metastasise to multiple organs. The cells remain wild type for TP53, diploid and genetically stable. In vivo tumour growth and in vitro proliferation of cells explanted from tumours are dependent on oestrogen.ConclusionWe have created a genetically defined model of ERα-positive human breast cancer based on normal HMECs that has the potential to model human oestrogen-dependent breast cancer in a mouse and enables the study of mechanisms involved in tumorigenesis and metastasis.

Pyometra with inguinal herniation of the left uterine horn and omentum in a Beagle dog

AbstractObjective: To describe a unique case of pyometra with inguinal herniation of the left uterine horn and omentum.Case summary: A 7‐year‐old, 19 kg, intact female Beagle dog presented for surgical treatment of presumptive pyometra and biopsy of a caudal abdominal mass in the left inguinal mammary gland region. Ventral midline celiotomy was performed, and a distended, fluid‐filled uterus with passage of the distal aspect of the left uterine horn through the left vaginal process into the inguinal canal was identified. The patient recovered uneventfully following ovariohysterectomy and left inguinal herniorrhaphy.New or unique information provided: This is the first documented report of inguinal herniation of a uterine horn associated with a pyometra.

A new species of the genus Physalaemus Fitzinger, 1826 (Anura, Leiuperidae) from Southeastern Brazil

Abstract A new species of the genus Physalaemus from the Atlantic Rain Forest of the state of Minas Gerais is described. It belongs to P. signifer species group and is characterized by well-developed vocal sac, second finger with the same size of the fourth, granulate dorsal skin, large inguinal gland with black ocelli, presence of dorso-lateral folds, and advertisement call composed by harmonic notes, generally four, being the last shorter than the others. Information on tadpole external morphology are also presented.

Description of A new species of the genus Adenomera (Amphibia, Anura, Leptodactylidae) from French Guiana

We describe a new species of the genus Adenomera from French Guiana. Collecting conditions, details about the localities and microhabitats are given. The advertisement call was recorded and is herein analyzed and described. Morphologi - cal and bioacoustic comparisons are drawn with other species of the genus. The new species is readily distinguished from other taxa by its distinctive coloration pattern, the occurrence of dorsolateral ridges and inguinal glands, and by the longer duration of the notes of its advertisement call. The taxonomy of Adenomera is evaluated with regard to current available knowledge.

Primary subcutaneous sacrococcygeal ependymoma: a case report and review of the literature

Extraspinal ependymomas are rare. The majority occur in the sacrococcygeal region. The subcutaneous variety accounts for approximately two thirds of cases, which are commonly misdiagnosed as a pilonidal cyst or sinus. Treatment is complete surgical resection. The role of coccygectomy is controversial. Adjuvant radiotherapy is of benefit to those with an incompletely excised tumour. Up to 20% metastasise, chiefly to the inguinal lymph glands, but pulmonary metastases are also reported. Palliative chemotherapy has not been shown to be of any benefit. Long term follow-up is important as metastases can occur up to 20 years after initial presentation. We report a 37-year-old woman with a subcutaneous sacrococcygeal ependymoma with iliac lymph nodal metastasis at presentation.

The Lymph Drainage of the Neoplastic Mammary Glands in the Bitch: A Lymphographic Study

The purpose of this investigation was to study the lymph drainage of the neoplastic mammary glands in the bitch using indirect lymphography. The main conclusions drawn from the study of 41 natural cases were as follows: the first or cranial thoracic and second or caudal thoracic neoplastic mammary glands usually drain into the ipsilateral axillary lymph nodes and rarely into the ipsilateral axillary and sternal lymph nodes, simultaneously. The third or cranial abdominal neoplastic mammary gland usually drains into the ipsilateral axillary and superficial inguinal lymph nodes simultaneously, but sometimes only cranially into the ipsilateral axillary lymph nodes. Rarely, it drains only caudally into the ipsilateral superficial inguinal and medial iliac lymph nodes, simultaneously. The fourth or caudal abdominal neoplastic mammary gland usually drains only caudally into the ipsilateral superficial inguinal lymph nodes. Rarely, it drains into the ipsilateral axillary and superficial inguinal lymph nodes simultaneously. The fifth or inguinal neoplastic mammary gland usually drains into the ipsilateral superficial inguinal lymph nodes but rarely, does it also drain into the ipsilateral popliteal lymph node and into a lymphatic plexus at the medial aspect of the ipsilateral thigh. Lymphatic connections between the neoplastic and adjacent normal mammary glands were demonstrated in only one case. The lymph drainage pattern of the neoplastic mammary glands is slightly different to that described in normal glands using the same radiographic method.

Overexpression of Activated Murine Notch1 and Notch3 in Transgenic Mice Blocks Mammary Gland Development and Induces Mammary Tumors

The mouse mammary tumor virus (MMTV) provirus was found to target the Notch1 gene, producing insertional mutations in mammary tumors of MMTV/neu transgenic (Tg) mice. In these mammary tumors, the Notch1 gene is truncated upstream of the transmembrane domain, and the resulting Notch1 intracellular domain (Notch1(intra)), deleted of most extracellular sequences, is overexpressed. Although Notch1(intra) transforms mammary epithelial cells in vitro, its role in mammary gland tumor formation in vivo was not studied. Therefore, we generated MMTV/Notch1(intra) Tg mice that overexpress murine Notch1(intra) in the mammary glands. We observed that MMTV/Notch1(intra) Tg females were unable to feed their pups because of impaired ductal and lobulo-alveolar mammary gland development. This was associated with decreased proliferation of ductal and alveolar epithelial cells during rapid expansion at puberty and in early pregnancy, as well as decreased production of beta-casein. Notch1(intra) repressed expression of the beta-casein gene promoter, as assessed in vitro with a beta-casein/luciferase reporter construct. The MMTV/Notch1(intra) Tg females developed mammary gland tumors, confirming the oncogenic potential of Notch1(intra) in vivo. Furthermore, MMTV/Notch3(intra) Tg mice exhibited a very similar phenotype. Thus, these Tg mice represent novel models for studying the role of Notch1 or Notch3 in the development and transformation of the mammary gland.

Altered Mammary Gland Development in Male Rats Exposed to Genistein and Methoxychlor

Genistein (GE) is a prevalent phytoestrogen whose presence in human and animal foods may affect biological actions of synthetic endocrine active compounds. We have previously reported that in utero and lactational exposure to high doses of GE or the endocrine active pesticide methoxychlor (MXC) caused mammary epithelial proliferation in 21-day-old male rats. Combined exposure to GE and MXC resulted in significant feminization of the male mammary glands. The goals of the current study were to evaluate mammary responses to GE and MXC at the adult stage and investigate relevant mechanisms. Following in utero, lactational exposure (through maternal diet), and direct dietary exposure, the inguinal mammary gland of male rats (90 days of age) was found to exhibit significant morphological alterations in the groups treated with GE and/or MXC compared to the control. GE exposure (at 300 and 800 ppm concentrations) caused lobular enlargement and epithelial proliferation, whereas MXC exposure (800 ppm) led to ductal elongation and lobular enlargement. Combining the two treatments caused prominent proliferation of both ducts and alveoli; secretory material was seen in readily recognizable alveolar lumens, which are absent in untreated male mammary. We also surveyed gene expression in the mammary tissue using a cDNA microarray and evaluated relevant protein factors. The results indicated that the treatment effects are likely due to interactions between steroid hormone receptor-mediated signals and growth factor-driven cellular pathways. The distinctive responses associated with the GE+MXC combination were likely linked to enhanced actions of insulin-like growth factor 1 and related downstream pathways.

Groin reconstruction after inguinal block dissection

Inguinal block dissection is a necessary component in the treatment of certain cancers. Cancer of the penis is not an uncommon malignancy in the Indian subcontinent and while no one questions the treatment of the primary lesion, the need to remove the inguinal lymph glands concurrently, remains a matter of great controversy. Never the less, the survival of patients with penile cancer depends solely on the presence or absence of metastasis to the inguinal lymph nodes. The hesitation in offering inguinal lymph node dissection in every case is significantly related to the morbidity of the procedure in an attempt to reduce these complications, skin flaps can be used to cover the groin. This article looks at various flaps that can be used in groin reconstruction.

Nuclear Localization of STAT5A Modified with O-Linked N-Acetylglucosamine and Early Involution in the Mammary Gland of Hirosaki Hairless Rat

Hirosaki hairless rat (HHR) is a mutant strain spontaneously derived from Sprague-Dawley rats (SDR), and its inheritance is autosomal recessive. In addition to hair loss, female HHRs show involution of the mammary gland at an early stage of lactation. In the present study we investigated the mammary gland development in HHR. Morphological examinations revealed that HHR mammary glands are underdeveloped in virgins and exhibit distended alveoli on day 1 of lactation (L1), followed by involution. Milk secretion was observed on L1 in HHR. Whey acidic protein and other proteins were increased in milk of HHR and heterozygous rats on SDS-polyacrylamide gel electrophoresis. Terminal deoxynucleotide transferase-mediated dUTP nick-end labeling assay revealed apoptosis induction in HHRs at an early stage of lactation. By Western blotting, signal transducer and activator of transcription (STAT) 5A levels in cytoplasmic and nuclear fractions of the mammary glands were not different between HHR and SDR on L1 and L7. Nuclear localization of STAT5A in HHR and SDR was confirmed by immunohistochemistry. Tyr-phosphorylated STAT5A was not detected in HHR but was detected in SDR nuclear fractions. Several proteins modified with O-linked N-acetylglucosamine (O-GlcNAc) were detected in HHR nuclear extract on L1, although not in SDR or heterozygous rats by Western blotting. When HHR nuclear extract was applied to wheat germ agglutinin-agarose, a part of STAT5A was recovered in bound fractions. STAT5A of SDR or heterozygous rat nuclei were not bound to the lectin. Electrophoretic mobility shift assay revealed that STAT5A modified with O-GlcNAc is bound to the STAT5-responsive element. These results indicate that the mammary glands of HHR showed terminal differentiation for a short period, followed immediately by involution. In HHR, STAT5A is modified with O-GlcNAc but is not Tyr-phosphorylated. This type of glycosylation is suggested to be involved in the transient activation of STAT5A in HHR.

Bcl-x L-Mediated Changes in Metabolic Pathways of Breast Cancer Cells : From Survival in the Blood Stream to Organ-Specific Metastasis

Bcl-x(L) protein plays a role in breast cancer dormancy, promoting survival of cells in metastatic foci by counteracting the proapoptotic signals in the microenvironment. The aim of this study was to identify phenotypes mediated by Bcl-x(L) in breast cancer cells that enhance in vivo survival of clinical metastases. 435/Bcl-x(L) or 435/Neo human breast cancer cells were injected into the inguinal mammary gland of nude mice, and tumors, metastases in lymph node, lung, and bone, and bloodstream surviving cells were examined. Proteomic analysis identified 17 proteins that were overexpressed (more than twofold) or underexpressed (less than twofold) in metastases. A protein interaction program allowed us to functionally associate peroxiredoxin 3, peroxiredoxin 2, carbonyl reductase 3, and enolase 1, suggesting a role for cellular responses to oxidative stress in metastasis organ selection. The prediction included proteins involved in redox systems, kinase pathways, and the ATP synthase complex. Furthermore, the interaction of redox proteins with enolase 1 suggests a connection between glycolysis and antioxidant pathways, enabling achievement of a high metastatic activity. In conclusion, Bcl-x(L) mediates a phenotype in which redox pathways and glycolysis are coupled to protect breast cancer metastatic cells during transit from the primary tumor to the metastatic state.

Estudo morfológico e molecular da mama de ratas castradas tratadas com isoflavona ou estrogênios

OBJETIVO: avaliar os efeitos das isoflavonas e dos estrogênios sobre a morfologia, a morfometria e a expressão do fator de crescimento vascular (VEGF) na mama de ratas adultas. MÉTODOS: Quarenta e cinco ratas, após 28 dias de ooforectomia, foram divididas em três grupos: CON - controle e os grupos que receberam medicação: ISO - isoflavona (100 mg/Kg) e ECE - estrogênios conjugados eqüinos (50 µg/Kg). Após 60 dias, parte das mamas foram fixadas em formol a 10% para processamento histológico, e outra parte congelada para a análise da expressão do VEGF pela técnica da reação em cadeia da polimerase com transcrição reversa (RT-PCR). Para análise dos resultados obtidos foram utilizados inicialmente a análise de variância (ANOVA). Quando houve significância, foi complementada com o teste de comparações múltiplas de Tukey-Kramer. RESULTADOS: Nos grupos CON e ISO as mamas apresentaram glândulas mamárias atróficas, sendo mais desenvolvidas no grupo ECE, onde se notou a presença de inúmeros ductos e de alvéolos mamários. A morfometria mostrou maior número de alvéolos no grupo ECE (12,3 ± 7,1* por mm²; p< 0,05%) do que nos outros grupos (CON = 1,4 ± 2,1 e ISO = 1,6 ± 3,8), sendo o volume dessas células maior (ECE = 27,4 ± 9,7 µm³, p < 0,05%) do que nos grupos CON (14,9 ± 4,9 µm³) e ISO (11,4 ± 6,9 µm³). O mesmo ocorreu em relação ao número de vasos sanguíneos [16,4 ± 1,5 por mm²(CON), 18,4 ± 2,1 (ISO) < 37,1 ± 4,1* (ECE), p < 0,05%]. Na análise do VEGF o grupo ECE apresentou maior expressão do que os grupos CON e ISO. CONCLUSÃO: nossos dados não evidenciaram efeito proliferativo no tecido mamário de ratas ooforectomizadas tratadas com isoflavona na dose de 100 mg/Kg durante 60 dias consecutivos.

Elf5 is essential for early embryogenesis and mammary gland development during pregnancy and lactation

Elf5 is an epithelial-specific ETS factor. Embryos with a null mutation in the Elf5 gene died before embryonic day 7.5, indicating that Elf5 is essential during mouse embryogenesis. Elf5 is also required for proliferation and differentiation of mouse mammary alveolar epithelial cells during pregnancy and lactation. The loss of one functional allele led to complete developmental arrest of the mammary gland in pregnant Elf5 heterozygous mice. A quantitative mRNA expression study and Western blot analysis revealed that decreased expression of Elf5 correlated with the downregulation of milk proteins in Elf5(+/-) mammary glands. Mammary gland transplants into Rag(-/-) mice demonstrated that Elf5(+/-) mammary alveolar buds failed to develop in an Elf5(+/+) mammary fat pad during pregnancy, demonstrating an epithelial cell autonomous defect. Elf5 expression was reduced in Prolactin receptor (Prlr) heterozygous mammary glands, which phenocopy Elf5(+/-) glands, suggesting that Elf5 and Prlr are in the same pathway. Our data demonstrate that Elf5 is essential for developmental processes in the embryo and in the mammary gland during pregnancy.

New Species of Physalaemus Fitzinger, 1826 from Southern Bahia, Brazil (Anura, Leptodactylidae)

A new species of Physalaemus belonging to the Physalaemus cuvieri species group is described from southern Bahia, Brazil. It inhabits the borders of Atlantic Rain Forest fragments, natural forest clearings, and cacao plantations. The new species is characterized by its medium size, robust body, warty skin, presence of inguinal glands, one pair of dorsal tubercles on the sacral region, and an interorbital black transversal stripe generally covering a pair of tubercles.

Gene expression profiles in mammary gland of male rats treated with genistein and methoxychlor

Humans and wildlife are frequently exposed to mixtures of natural and synthetic endocrine-active compounds. To understand the impact of dietary phytoestrogen on the susceptibility to synthetic chemicals in the environment, we studied the effects of a binary mixture consisting of the isoflavone genistein and the pesticide methoxychlor on the development of the mammary gland. Sprague–Dawley rats were exposed to genistein at 800 ppm, methoxychlor at 800 ppm, or their combination through dietary administration to dams during pregnancy and lactation and to the offspring directly after weaning. At post-natal day (PND) 90, offspring rats were killed and their inguinal mammary glands collected for gene expression analysis utilizing the Clontech Atlas Rat 1.2 cDNA array, which contains probes for 1176 genes. Treatment with both genistein and methoxychlor altered gene expression profiles of the mammary glands in male rats, and the effects were more prominent in the combination treatment than the single-compound groups. Specific gene changes suggested that treatments affected the stromal and epithelial compartments of the mammary, involving genes controlling growth factor signaling, apoptosis, and tissue remodeling. This study demonstrates that dietary phytoestrogens in combination with a synthetic endocrine-active chemical can cause unique effects in endocrine-responsive tissues and highlights the importance of studying the effects of chemical combinations on the multiple biological processes underlying toxicological responses.