Psychosocial stressors and mammary tumor growth: an animal model

Parental loss at age birth to 21 years and daughters' breast cancer and tumor characteristics

BACKGROUND

Adverse events in childhood are linked to cancer risk across the life course, but evidence is lacking regarding parental death during childhood and breast cancer characteristics. We investigated whether women who experienced parental loss in childhood have a higher incidence of breast cancer and are at higher risk of aggressive disease.

METHODS

The Child Health and Development Studies (CHDS) consists of more than 15 000 families that enrolled during mothers' pregnancies between 1959 and 1967; family members were followed for cancer incidence and cause-specific mortality. We constructed an analytical cohort of all live-born CHDS daughters (N = 9169) linked to their parents' cause and date of death. We estimated adjusted hazard ratios of incident breast cancer, disease stage at diagnosis, and tumor hormone receptor expression for parental loss in Cox models adjusted for race, maternal breast cancer, and paternal age. Generalized linear models estimated associations between breast density and parental loss among a subsample of CHDS daughters (n = 610) with available mammography reports.

RESULTS

In total, 137 CHDS daughters were diagnosed with breast cancer by age 52 years, and 654 daughters had lost 1 or both parents when they were 21 years of age or younger. Loss of both parents was associated with breast cancer incidence (adjusted hazard ratio =  4.69, 95% CI = 1.68 to 13.04); late-stage disease at diagnosis (adjusted hazard ratio =  9.47, 95% CI = 1.38 to 64.84); and ERBB2 (formerly HER2)-positive, progesterone receptor-negative, and estrogen receptor-negative tumors. Loss of mother or father was associated with ERBB2-positive tumors. Breast density in the premenopause window was associated with loss of a mother or both parents.

CONCLUSION

In a multigenerational cohort with well-defined cancer outcomes and validated cause-of-death data, life-course risk of breast cancer was 4.69 times higher among participants who had lost both parents during childhood. Subanalyses showed that parental loss was associated with late stage at diagnosis and tumor hormone markers of aggressive disease. Parental death during childhood could be added to medical histories to indicate a need for counseling on prevention and early detection of breast cancer.

UVB Induces Sympathetic Nervous System Activation and Norepinephrine Secretion to Regulate The Skin Color of Mice Through the β2-AR/AP-1 Pathway in Epidermal Keratinocytes

The aim of this study was to investigate how ultraviolet B (UVB) light regulates AP-1 expression via the β2-adrenergic receptor (β2-AR) in epidermal keratinocytes, which in turn regulates melanin synthesis in melanocytes, thereby modulating downstream melanin production in skin hair follicles and altering mouse skin color. We established a UV-irradiated mouse model to investigate the effects of UV radiation on changes in skin color. By measuring changes in the expression of genes related to cutaneous sympathetic nerves, norepinephrine synthesis and melanin synthesis, we investigated the relationship between β2-AR expression and cutaneous melanogenesis and determined the localization of β2-AR in cells. The results of the siRNA-mediated transfection of keratinized cells with downregulated β2-AR expression were further verified in vitro. Our results suggest that UVB alters the color of the dorsal skin in mice by activating the AP-1/IL-6 pathway, which triggers the sympathetic release of norepinephrine, thereby increasing β2-AR expression in keratinocytes. Overall, our study improves the current understanding of how UVB light influences skin color changes and highlights the complex interplay between ultraviolet radiation and skin physiology.

Nature and Determinants of Fear of Cancer Recurrence After Endoscopic Submucosal Dissection for Early Gastric Cancer: A Cross-Sectional Study

Gastric cancer is one of the most prevalent tumors in China and other countries, with high morbidity and mortality. Fear of cancer recurrence is common among cancer survivors. Fear of cancer recurrence experiences and psychological interventions have been investigated in breast and other cancers. However, this phenomenon and associated factors have not been evaluated in early gastric cancer survivors in China. The objective of this study was to investigate the nature of fear of cancer recurrence and influencing factors in Chinese patients with early gastric cancer treated with endoscopic submucosal dissection. This cross-sectional study in two centers included 312 early gastric cancer patients who answered self-report questionnaires and were treated with endoscopic submucosal dissection between June 2022 and May 2023 to assess fear of cancer recurrence. Gender, family history of gastrointestinal tumor, tumor recurrence, Helicobacter pylori infection, disease perception, and self-perceived burden were significant factors influencing fear of cancer recurrence (p < .05). More than half of early gastric cancer patients have fear of cancer recurrence, and how to deal with it has become a key issue in the postoperative care of patients. Medical professionals should address these factors to reduce fear of cancer recurrence in at-risk patients.

Catecholamines Promote Ovarian Cancer Progression through Secretion of CXC-Chemokines

Considerable evidence has accumulated in the last decade supporting the notion that chronic stress is closely related to the growth, metastasis, and angiogenesis of ovarian cancer. In this study, we analyzed the conditioned media in SKOV3 ovarian cancer cell lines treated with catecholamines to identify secreted proteins responding to chronic stress. Here, we observed that epinephrine and norepinephrine enhanced the secretion and mRNA expression of CXC-chemokines (CXCL1, 2, 3, and 8). Neutralizing antibodies to CXCL8 and CXCL8 receptor (CXCR2) inhibitors significantly reduced catecholamine-mediated invasion of SKOV3 cells. Finally, we found that the concentration of CXCL1 and CXCL8 in the plasma of ovarian cancer patients increased with stage progression. Taken together, these findings suggest that stress-related catecholamines may influence ovarian cancer progression through the secretion of CXC-chemokines.

'Invisible actors'-How poor methodology reporting compromises mouse models of oncology: A cross-sectional survey

The laboratory mouse is a key player in preclinical oncology research. However, emphasis of techniques reporting at the expense of critical animal-related detail compromises research integrity, animal welfare, and, ultimately, the translation potential of mouse-based oncology models. To evaluate current reporting practices, we performed a cross-sectional survey of 400 preclinical oncology studies using mouse solid-tumour models. Articles published in 2020 were selected from 20 journals that specifically endorsed the ARRIVE (Animal Research: Reporting of In Vivo Experiments) preclinical reporting guidelines. We assessed reporting compliance for 22 items in five domains: ethical oversight assurance, animal signalment, husbandry, welfare, and euthanasia. Data were analysed using hierarchical generalised random-intercept models, clustered on journal. Overall, reporting of animal-related items was poor. Median compliance over all categories was 23%. There was little or no association between extent of reporting compliance and journal or journal impact factor. Age, sex, and source were reported most frequently, but verifiable strain information was reported for <10% of studies. Animal husbandry, housing environment, and welfare items were reported by <5% of studies. Fewer than one in four studies reported analgesia use, humane endpoints, or an identifiable method of euthanasia. Of concern was the poor documentation of ethical oversight information. Fewer than one in four provided verifiable approval information, and almost one in ten reported no information, or information that was demonstrably false. Mice are the "invisible actors" in preclinical oncology research. In spite of widespread endorsement of reporting guidelines, adherence to reporting guidelines on the part of authors is poor and journals fail to enforce guideline reporting standards. In particular, the inadequate reporting of key animal-related items severely restricts the utility and translation potential of mouse models, and results in research waste. Both investigators and journals have the ethical responsibility to ensure animals are not wasted in uninformative research.

The Dysfunction of Carcinogenesis- and Apoptosis-Associated Genes that Develops in the Hypothalamus under Chronic Social Defeat Stress in Male Mice

Chronic social stress caused by daily agonistic interactions in male mice leads to a mixed anxiety/depression-like disorder that is accompanied by the development of psychogenic immunodeficiency and stimulation of oncogenic processes concurrently with many neurotranscriptomic changes in brain regions. The aim of the study was to identify carcinogenesis- and apoptosis-associated differentially expressed genes (DEGs) in the hypothalamus of male mice with depression-like symptoms and, for comparison, in aggressive male mice with positive social experience. To obtain two groups of animals with the opposite 20-day social experiences, a model of chronic social conflict was used. Analysis of RNA-Seq data revealed similar expression changes for many DEGs between the aggressive and depressed animals in comparison with the control group; however, the number of DEGs was significantly lower in the aggressive than in the depressed mice. It is likely that the observed unidirectional changes in the expression of carcinogenesis- and apoptosis-associated genes in the two experimental groups may be a result of prolonged social stress (of different severity) caused by the agonistic interactions. In addition, 26 DEGs were found that did not change expression in the aggressive animals and could be considered genes promoting carcinogenesis or inhibiting apoptosis. Akt1, Bag6, Foxp4, Mapk3, Mapk8, Nol3, Pdcd10, and Xiap were identified as genes whose expression most strongly correlated with the expression of other DEGs, suggesting that their protein products play a role in coordination of the neurotranscriptomic changes in the hypothalamus. Further research into functions of these genes may be useful for the development of pharmacotherapies for psychosomatic pathologies.

Genetic Variation and Immunohistochemical Localization of the Glucocorticoid Receptor in Breast Cancer Cases from the Breast Cancer Care in Chicago Cohort

BACKGROUND

Glucocorticoid, one of the primary mediators of stress, acts via its receptor, the glucocorticoid receptor (GCR/NR3C1), to regulate a myriad of physiological processes. We measured the genetic variation and protein expression of GCR, and the genes that regulate GCR function or response and examined whether these alterations were associated with breast cancer clinicopathological characteristics.

METHOD

We used samples from a multiracial cohort of breast cancer patients to assess the association between breast cancer characteristics and the genetic variants of single nucleotide polymorphisms (SNPs) in GCR/NR3C1, FKBP5, Sgk1, IL-6, ADIPOQ, LEPR, SOD2, CAT, and BCL2.

RESULTS

Several SNPs were associated with breast cancer characteristics, but statistical significance was lost after adjustment for multiple comparisons. GCR was detected in all normal breast tissues and was predominantly located in the nuclei of the myoepithelial cell layer, whereas the luminal layer was negative for GCR. GCR expression was significantly decreased in all breast cancer tissue types, compared to nontumor tissue, but was not associated with breast cancer characteristics. We found that high nuclear GCR expression was associated with basal cell marker cytokeratin 5/6 positivity.

CONCLUSION

GCR expression is reduced in breast cancer tissue and correlates with the basal cell marker CK5/6.

Chronic Unpredictable Mild Stress Accelerates the Growth of Bladder Cancer in a Xenograft Mouse Model

Objective

Chronic psychological stress is common in patients with bladder cancer. An increasing number of evidence demonstrated that psychiatric disorder leads to worse prognostic outcomes in bladder cancer. This study was to investigate the effects of chronic psychological stress on the growth of bladder cancer and its potential mechanisms.

Methods

A xenograft mouse model was established by subcutaneously implanting the human bladder cancer cell line T24 into nude mice. All of the tumor-bearing mice (N=20) were randomly separated into two groups. Mice in the control group were subjected to normal feeding conditions, while in another group, a chronic unpredictable mild stress (CUMS) model was established, in which mice were exposed to various types of stressors. Various analyses were performed on parameters including the tumor volume, tumor weight, expression of Caspase-3 and VEGF, proportion of Ki-67 positive cells (Ki-67 index), microvessel density (MVD) and serum concentrations of epinephrine and cortisol.

Results

In the CUMS group, the growth of transplanted tumors was distinctly accelerated, with the weight of removed tumors at the end of experiment increased by 34.07% compared to that of the control. Serum levels of epinephrine and cortisol determined by ELISA were significantly increased by CUMS. Immunohistochemistry and Western blot analysis showed that the expression of Caspase-3 was downregulated, whereas the expression of VEGF was upregulated in the CUMS group. Meanwhile, CUMS could increase the Ki-67 index and MVD.

Conclusion

Our research supports the hypothesis that CUMS could affect the growth of bladder cancer in nude mice, indicating that the intervention of chronic psychological stress may be a possible therapeutic strategy for bladder cancer.

Might anxiety disorders promote head and neck cancer development?

Cancer patients present a higher risk of experiencing anxiety disorders (AD). However, it is not clear if AD might be associated with cancer development. Thus, our study aimed to evaluate if AD might be related to head and neck squamous cell carcinoma (HNSCC) development. The combination of an applied animal basic study and a retrospective diagnostic case and control study in patients was performed. As a result, we obtained that stress reduced the locomotor activity of the animals in the group stress and stress + 4NqO (p < 0.0001). The stress showed no influence on the progression of neoplasia in mice. In the same way, the case group did not present differences in anxiety scores in comparison to control. Moreover, no association between HNSCC staging and anxiety scores was observed. In conclusion, our in vivo findings in humans and animals have shown that there is no relationship between AD and oral squamous cell carcinoma.

Stress et cancer : mythes et réalités

Les théories profanes émises par les patients et certains ouvrages destinés au grand public alimentent l’idée que le stress psychologique peut influencer le risque de survenue de cancer. Les études consultées sur cette question semblent donner des résultats contradictoires. D’un côté, ces théories peuvent sembler étayées par les résultats d’études expérimentales portant sur les corrélats physiologiques du stress sur des voies neuro-immunoendocrinologiques (perturbations immunitaires, altération de l’axe hypothalamohypophyso- surrénalien), métaboliques et cellulaires (stress oxydatif, dégénérescence cellulaire) pouvant être impliquées dans la tumorigenèse. De l’autre, les études épidémiologiques prospectives fondées sur une méthodologie robuste ne trouvent généralement pas d’association entre exposition au stress et développement ultérieur d’un cancer. Par ailleurs, les méta-analyses suggèrent l’existence de biais de publication pouvant surestimer le poids des études « positives ». Quand bien même une association est retrouvée, le caractère observationnel des études épidémiologiques et donc la possibilité de facteurs de confusion empêchent d’établir un lien de causalité entre l’exposition au stress et un risque majoré de cancer. En ce qui concerne les mécanismes d’une éventuelle relation causale directe, il faut souligner la difficulté d’extrapoler à l’être humain des résultats obtenus chez d’autres animaux, et s’assurer de bien prendre en compte la présence de facteurs comportementaux confondants ou médiateurs comme une mauvaise hygiène de vie alimentaire, la consommation de tabac et d’alcool, les expositions professionnelles, etc. Selon les recommandations du National Cancer Institute (NCI, 2012), les connaissances actuellement disponibles ne permettent pas d’établir un lien de causalité entre stress et augmentation du risque de cancer. Si le professionnel de soin psychique ne doit donc pas cautionner ce lien hypothétique au risque de culpabiliser le patient, il gardera à l’esprit, d’une part, que le cancer peut en revanche générer un stress bien réel au quotidien chez les patients atteints par cette maladie et, d’autre part, que ces théories « profanes » peuvent parfois témoigner d’un mécanisme de défense contre ce stress.

Patterns of calcium signaling: A link between chronic emotions and cancer

Intra and inter-cellular calcium signaling is present in all types of cells and body tissues. In the human brain, calcium currents and waves are related to mental activities, including emotions. We present a theoretical interpretation of these phenomena suggesting their involvement in chronic emotional patterns and in the pathology of cancer. Recent developments on biophysics, translational biology and psychoneuroendocrinoimmunology (PNEI) can support explanatory hypotheses about the link between emotional stresses and the origin and development of different types of tumor cells. Chronic stresses may cause perturbations of rhythms of the PNEI system, excessive activation of HPA axis and abnormal activation of calcium signals in somatic tissues, with deleterious effects on different parts of the body. The increasing of calcium signaling inside cells may lead to a deregulation of different pathways and epigenetic systems that promote the production of genomic mutations in a second phase. In particular, the hyperactivation of the transcription nuclear factor kappaB (NF-κB), if is not counterbalanced by the following activation of the nuclear factor (erythroid-derived 2)-like 2 (NFE2L2 or Nrf2), increases the production of oxidative catabolites, as the advanced glycation end products (AGE), which play a key role in the progression of different types of cancer and other degenerative diseases. Cortisol binding to glucocorticoid receptor (GR) reduces the activity of both NF-κB and Nrf2 inside the cells but inhibits the cellular immunity and the anabolic processes of tissue regeneration. The tissue atrophy and the defective anti-ageing mechanisms promotes the tumoral cells growth and their escape from the immune-surveillance.

Perception matters: Stressful life events increase breast cancer risk

OBJECTIVE

The relationship between psychological stress and breast cancer risk is unclear. The present study sought to understand how stressfulness appraisal of salient Life Events (LEs) influences breast cancer risk.

METHODS

A case-control design was used and included 664 female cases identified through the Cancer Surveillance Program of Orange County, CA and 203 female population-based controls. A LE questionnaire determined if events occurred prior to breast cancer diagnosis and if these events were considered to be stressful or not. Multivariate unconditional logistic regression was used to calculate ORs while adjusting for known breast cancer covariates.

RESULTS

Cumulative adverse LEs perceived as stressful were associated with increased breast cancer risk in a dose response fashion (OR = 1.63, 95% CI = 1.00-2.66, P_trend = 0.045). Conversely, events perceived as non-stressful did not have a significant impact on breast cancer risk. Previous personal illness was directly related to increased breast cancer risk, whether perceived as stressful (OR = 2.84, 95% CI = 1.96-4.11) or non-stressful (OR = 3.47, 95% CI = 1.34-8.94). Abortion and relocation were observed to have a protective effect on breast cancer risk only when reported as stressful (OR = 0.54, 95% CI = 0.32-0.92; OR = 0.63, 95% CI = 0.43-0.93, respectively). Pre/Peri-menopausal women who were nulliparous or who had their first child at ≥30 years of age were especially prone to the effects of appraised stress on increased breast cancer risk.

CONCLUSIONS

This study underscores the importance of stressfulness appraisal when determining the effect of major LEs on breast cancer risk. Our results support incorporating assessments of perceived stressfulness in future epidemiological investigation of this topic.

Negative Valence Life Events Promote Breast Cancer Development

BACKGROUND

The influence of stress on breast cancer risk remains unknown. The goal of the present study was to determine the effect of stress in the form of salient positive and negative valence life events (LEs) on primary invasive breast cancer risk. We hypothesized that salient negative LEs would increase breast cancer risk and salient positive LEs would attenuate this increased risk.

PATIENTS AND METHODS

We used a case-control design with 664 cases identified through the Cancer Surveillance Program of Orange County and 203 population-based controls. Participants completed a risk factor questionnaire, which included a LE section. Fourteen salient LEs of positive or negative valence were used to quantify stress exposure. A baseline model was constructed, and odds ratios (ORs) were calculated using multivariate unconditional logistic regression.

RESULTS

Negative LEs were associated with increased breast cancer risk. The OR for ≥ 4 negative LEs showed a 2.81-fold increase in breast cancer risk (OR, 2.81; 95% confidence interval [CI], 1.47-5.36). A significant dose-response relationship between lifetime negative valence LEs and breast cancer risk was found. Previous personal illness increased breast cancer risk by 3.6-fold (OR, 3.60; 95% CI, 2.50-5.20). In contrast, abortion was associated with a 45% decrease in breast cancer risk (OR, 0.55; 95% CI, 0.34-0.89). Salient positive LEs did not have a significant effect on breast cancer risk. However, they seemed to buffer the adverse effect of salient negative LEs on breast cancer risk.

CONCLUSION

The findings from the present study support the role of salient negative LEs in promoting breast cancer development, with a possible buffering effect of salient positive LEs.

Mammary Tumors Induce Central Pro-inflammatory Cytokine Expression, but Not Behavioral Deficits in Balb/C Mice

Breast cancer survivors are more likely to develop mood disorders and cognitive deficits than women in the general population. Previous studies suggest that peripheral tumors elicit central pro-inflammatory cytokine production, in turn leading to depression and cognitive deficits. In the current study, two cohorts of female Balb/C mice received bilateral orthotopic injections of syngeneic 67NR, 4T07, or 4T1cells (1 × 105 cells per injection) to induce mammary tumors. Approximately three weeks later, learned fear (via fear conditioning) or depressive-like behavior (via tail suspension and forced swim test) was assessed. Proinflammatory cytokine levels were increased in the serum (IL-1β, TNFα, IFNγ) and livers (IL-1β, IL-6, TNFα) of mice with 4T07 or 4T1 tumors compared to 67NR tumors and the vehicle control. IL-1β was increased in both the hippocampus and cortex of mice injected with 4T07 or 4T1 cell lines relative to the other treatment groups. However, mammary tumors had no effect on hippocampal doublecortin + and did not alter depressive-like behavior or learned fear. These data demonstrate that similarly sized tumors can produce differential immune responses and that tumor-induced central pro-inflammatory cytokine production can exist in the absence of depressive-like behavior or cognitive deficits.

Social isolation induces autophagy in the mouse mammary gland: link to increased mammary cancer risk

Social isolation is a strong predictor of early all-cause mortality and consistently increases breast cancer risk in both women and animal models. Because social isolation increases body weight, we compared its effects to those caused by a consumption of obesity-inducing diet (OID) in C57BL/6 mice. Social isolation and OID impaired insulin and glucose sensitivity. In socially isolated, OID-fed mice (I-OID), insulin resistance was linked to reduced Pparg expression and increased neuropeptide Y levels, but in group-housed OID fed mice (G-OID), it was linked to increased leptin and reduced adiponectin levels, indicating that the pathways leading to insulin resistance are different. Carcinogen-induced mammary tumorigenesis was significantly higher in I-OID mice than in the other groups, but cancer risk was also increased in socially isolated, control diet-fed mice (I-C) and G-OID mice compared with that in controls. Unfolded protein response (UPR) signaling (GRP78; IRE1) was upregulated in the mammary glands of OID-fed mice, but not in control diet-fed, socially isolated I-C mice. In contrast, expression of BECLIN1, ATG7 and LC3II were increased, and p62 was downregulated by social isolation, indicating increased autophagy. In the mammary glands of socially isolated mice, but not in G-OID mice, mRNA expressions of p53 and the p53-regulated autophagy inducer Dram1 were upregulated, and nuclear p53 staining was strong. Our findings further indicated that autophagy and tumorigenesis were not increased in Atg7(+/-) mice kept in social isolation and fed OID. Thus, social isolation may increase breast cancer risk by inducing autophagy, independent of changes in body weight.

Sympathectomy reduces tumor weight and affects expression of tumor-related genes in melanoma tissue in the mouse

Accumulated evidence indicates that sympathetic nerves may potentiate tumor growth, including melanoma. To elucidate possible mechanisms for this effect, we performed chemical sympathectomy by intraperitoneal (i.p.) injection of the neurotoxin 6-hydroxydopamine hydrobromide (100 mg/kg of body weight); in nine adult male C57BL/6J mice; nine control mice received i.p. vehicle (VEH). Seven days later, all mice were injected subcutaneously with 3 × 10(3) B16-F10 melanoma cells. Mice were euthanized 20 d after injection of melanoma cells, for measurement of tumor weight and expression of genes related to sympathetic signaling, apoptosis, hypoxia and angiogenesis in tumor tissue. To assess potential involvement of the hypothalamo-pituitary-adrenocortical axis in the effect of sympathectomy on melanoma growth, concentrations of plasma corticosterone and level of glucocorticoid receptor mRNA in tumor tissue were determined. We found that sympathectomy significantly attenuated melanoma growth (tumor weight 0.29 ± 0.16 g versus 1.02 ± 0.30 g in controls; p < 0.05). In tumor tissue from sympathectomized mice, we found significantly increased gene expression (measured by real-time PCR), relative to VEH-injected controls, of tyrosine hydroxylase, neuropeptide Y and glucocorticoid receptor (all p < 0.05), and alpha1, beta1 and beta3 adrenergic receptors (all p < 0.025), and factors related to apoptosis (Bcl-2 and caspase-3; p < 0.05) and hypoxia (hypoxia inducible factor 1 alpha) (p = 0.005). Plasma corticosterone concentrations were significantly elevated (p < 0.05) in these mice. Our findings indicate that sympathectomy induces complex changes in the tumor microenvironment reducing melanoma growth. Such complex changes should be considered in the prediction of responses of cancer patients to interventions affecting sympathetic signaling in tumor tissue and its environment.

Stress, catecholaminergic system and cancer

Stress as a modern civilization factor significantly affects our lives. While acute stress might have a positive effect on the organism, chronic stress is usually detrimental and might lead to serious health complications. It is known that stress induced by the physical environment (temperature-induced cold stress) can significantly impair the efficacy of cytotoxic chemotherapies and the anti-tumor immune response. On the other hand, epidemiological evidence has shown that patients taking drugs known as β-adrenergic antagonists ("β-blockers"), which are commonly prescribed to treat arrhythmia, hypertension, and anxiety, have significantly lower rates of several cancers. In this review, we summarize the current knowledge about catecholamines as important stress hormones in tumorigenesis and discuss the use of β-blockers as the potential therapeutic agents.

Pathobiology of aging mice and GEM: background strains and experimental design

The use of induced and spontaneous mutant mice and genetically engineered mice (and combinations thereof) to study cancers and other aging phenotypes to advance improved functional human life spans will involve studies of aging mice. Genetic background contributes to pathology phenotypes and to causes of death as well as to longevity. Increased recognition of expected phenotypes, experimental variables that influence phenotypes and research outcomes, and experimental design options and rationales can maximize the utility of genetically engineered mice (GEM) models to translational research on aging. This review aims to provide resources to enhance the design and practice of chronic and longevity studies involving GEM. C57BL6, 129, and FVB/N strains are emphasized because of their widespread use in the generation of knockout, transgenic, and conditional mutant GEM. Resources are included also for pathology of other inbred strain families, including A, AKR, BALB/c, C3H, C57L, C58, CBA, DBA, GR, NOD.scid, SAMP, and SJL/J, and non-inbred mice, including 4WC, AB6F1, Ames dwarf, B6, 129, B6C3F1, BALB/c,129, Het3, nude, SENCAR, and several Swiss stocks. Experimental strategies for long-term cross-sectional and longitudinal studies to assess causes of or contributors to death, disease burden, spectrum of pathology phenotypes, longevity, and functional healthy life spans (health spans) are compared and discussed.

Individual differences in pre-carcinogen cytokine and corticosterone concentrations and depressive-like behavior predict tumor onset in rats exposed to a carcinogen

Individual variation in the susceptibility to chronic disease can be attributed to both genetic and environmental factors. Measures of the immune, nervous, and endocrine systems are predictive of survival outcomes after a chronic disease is diagnosed. However, determining biomarkers or "traits" that predict risk before chronic disease development remains elusive. In this study, natural individual variation in circulating cytokines, corticosterone, and depressive-like behaviors (using the Porsolt forced swim test) were measured in female rats before induction of mammary tumors using a chemical carcinogen (N-nitroso-N-methylurea). Early tumor onset was associated with relatively high (but within the physiologically typical range) circulating cytokine concentrations (IL-1α, IL-1β, TNFα) and depressive-like behavior and with relatively low corticosterone concentrations, all of which were assessed at baseline before carcinogen treatment. Multiple regression analyses indicated that IL-1β was primarily responsible for the variation in tumor onset when controlling for corticosterone concentration. These results suggest that the susceptibility to tumor initiation and/or growth may be related to individual differences in baseline immune and endocrine physiology and emotional tone present at the time of carcinogen exposure. Investigation of the mechanistic relevance of these individual differences may lead to prophylactic approaches to cancer treatment in the context of carcinogen exposure.

Stress and breast cancer: from epidemiology to molecular biology

Stress exposure has been proposed to contribute to the etiology of breast cancer. However, the validity of this assertion and the possible mechanisms involved are not well established. Epidemiologic studies differ in their assessment of the relative contribution of stress to breast cancer risk, while physiological studies propose a clear connection but lack the knowledge of intracellular pathways involved. The present review aims to consolidate the findings from different fields of research (including epidemiology, physiology, and molecular biology) in order to present a comprehensive picture of what we know to date about the role of stress in breast cancer development.

Sex-specific social regulation of inflammatory responses and sickness behaviors

In many mammals, the availability of familiar conspecifics in the home environment can affect immune function and morbidity. Numerous sex differences exist in immune responses, but whether the social environment impacts the immune system differently in males and females is not fully understood. This study examined behavioral and physiological responses to simulated bacterial infection in adult male and female Wistar rats housed either with three same-sex non-siblings (Group) or alone (Isolate). Rats were injected with bacterial lipopolysaccharide (Escherichia coli LPS; 150 microg/kg, i.p.), and behavioral (orectic, locomotor, and social) and physiological (thermoregulatory, cytokine, and corticosterone) inflammatory responses were measured. Among males, LPS-induced fever, suppressed locomotor activity, and inhibited feeding behavior and the magnitude of these responses were greater in Isolate relative to Group housed individuals. In contrast, among females group housing exacerbated behavioral and physiological symptoms of simulated infection. LPS treatments elicited IL-1beta production in all groups, but plasma IL-1beta concentrations were higher and peaked earlier in Isolate relative to Group males, and in Group relative to Isolate females. Furthermore, plasma concentrations of TNFalpha and IL-2 were higher in Group relative to Isolate males. Plasma corticosterone concentrations did not vary as a function of social housing conditions. Together, the data indicate that the social environment markedly influences innate immune responses. Group housing exacerbates inflammatory responses and sickness behaviors in females, but attenuates these responses in males. These sex differences are mediated in part by differential effects of the social environment on pro- and anti-inflammatory cytokine production.

Adrenaline induces chemoresistance in HT-29 colon adenocarcinoma cells

Psychological distress and its ensuing chronic elevation of plasma catecholamines (adrenaline and noradrenaline) lead to poor response of tumors to chemotherapy, and constitute a poor prognostic factor for survival. Colorectal cancer patients suffer from various forms of psychological stress reflected in elevated plasma catecholamines, and their cancer cells express adrenergic receptors. Our objective was to investigate whether adrenergic activation contributes to the chemoresistance of colon cancers, and to explore the signal transduction pathway involved in the activation. The mRNA expression of the ABCB1 gene (previously MDR1) in human colon carcinoma HT-29 cell line was measured after treatment with an adrenergic receptor agonist (adrenaline) and various antagonists (propranolol, prazosin, and yohimbine). The function of P-glycoprotein, the protein product of the ABCB1 gene, was assessed by rhodamine 123 (Rh123)-retention assay, and chemosensitivity was determined by evaluating the cytotoxicity of 5-fluorouracil (5-FU) on the tumor cells. Increased ABCB1 mRNA expression and P-glycoprotein function levels in HT-29 cells by adrenaline was dose-dependent. This was accompanied by promotion of Rh123 efflux, and resistance to the growth-inhibiting effect of 5-FU in the tumor cells. The alpha2-adrenergic receptor antagonist yohimbine completely abolished the induction of ABCB1 mRNA, the stimulatory effect of adrenaline on Rh123 efflux, and the growth-inhibiting effect of 5-FU. The alpha1-adrenergic receptor and beta-adrenergic receptor antagonists did not inhibit the induction of ABCB1. The stimulating effects were coupled with extracellular receptor kinase 1/2 (Erk1/2) phosphorylation, but were not associated with protein kinase A activity. We conclude that adrenaline induces multidrug resistance in colon cancer cells by upregulating ABCB1 gene expression via alpha2-adrenergic receptors, and such effects were associated with the mitogen activated protein kinase (MAPK) pathway.

Effects of individual housing on behavior and resistance to Ehrlich tumor growth in mice

This study analyzed in Balb/C mice the effects of individual housing on behavior, serum corticosterone and resistance to Ehrlich tumor growth. Mice (60 days old) were individually (IH) or grouped housed (G) (10-12 animals/cage) for 14-21 days. The 1st day of the housing condition was considered experimental day 1 (ED1). Results showed that on ED21, IH mice, when compared to G mice, presented no differences on corticosterone serum levels when kept undisturbed; however, an increased level of this hormone was observed in IH mice after an immobilization stress challenge. An increased time spent in the plus-maze closed arms and a decreased time in the open arms were also observed in IH mice. When compared to G animals, after inoculation with 10(5) Ehrlich tumor cells on ED1, IH mice presented an increase in volume of ascitic fluid and number of tumor cells. The survival time of IH mice was also shorter than that measured in G animals. Furthermore, IH mice injected with a different number of tumor cells on ED1 always presented increased Ehrlich tumor cells than G group. Interestingly, these effects were not observed when the tumor cells injection was done on ED4. These results suggest that individual-housing conditions induce an altered immune-endocrine response and, at the same time, decrease animals' resistance to Ehrlich tumor growth. It is proposed that the neural link between the behavioral and immunological changes observed after the stress of individual housing might involve the activation of the HPA axis.

Relations between different coping strategies for social stress, tumor development and neuroendocrine and immune activity in male mice

This study analyzes the effects of acute social stress and different coping strategies employed in response to it on the development of B16F10 melanoma pulmonary metastases, the activation of the HPA axis and the NKG2D receptor expression. To this end, male OF1 mice were subjected to 24h of social stress using the sensorial contact model. This model includes three 5-min sessions of direct social interaction with resident cagemates selected for consistent levels of aggression. Subjects' behavior was videotaped and assessed. Six days after the first social interaction (1st social stress), the animals were inoculated with tumor cells or vehicle, and six days later, both tumor-bearing and non tumor-bearing mice were subjected to a second 24h sensorial contact social stress session (2nd social stress). One hour after the 2nd social interaction, corticosterone levels and NKG2D receptor expression were determined. Lung metastatic foci numbers were determined 21 days after inoculation (15 days post-stress). Social stress increased the number of pulmonary metastases and the serum corticosterone level. A combination of cluster and discriminant analyses established the existence of two types of coping strategies: (1) a passive-reactive strategy characterized by subjects dedicating a greater percentage of time to submission, flee and avoidance behaviors; and (2) an active-proactive strategy, characterized by subjects dedicating a greater percentage of time to attack and non social exploration behaviors. Subjects belonging to the passive-reactive group were found to have a higher number of tumor foci, a higher level of corticosterone and a lower NKG2D receptor expression than subjects in the active-proactive group. These data indicate the relationship between different coping strategies for social stress and tumor development.

Stress-induced differences in primary and secondary resistance against bacterial sepsis corresponds with diverse corticotropin releasing hormone receptor expression by pulmonary CD11c+ MHC II+ and CD11c- MHC II+ APCs

Stress responses have been associated with altered immunity and depending upon the type of stressor, can have diverse effects on disease outcomes. As the first line of defense against potential pathogens, alterations in cellular immune responses along the respiratory tract can have a significant impact on the manifestation of local and systemic disease. Utilizing a murine model of respiratory pneumonia, the current study investigated the effects of restraint stress on the induction of primary and secondary immunity along the respiratory tract, influencing host susceptibility. Female CD-1 mice were subjected to three hours of restraint stress over a period of four days followed by primary and secondary Streptococcus pneumoniae infection via intranasal route. Stress exposure led to increased retention of bacterial carriage in the lungs, enhanced polymorphonuclear cells and a preferential decrease in pulmonary CD11c(+) MHC II(+) cells resulting in delayed lethality during primary infection but significant impairment of acquired immune protection after secondary infection. We also provide evidence to support a role for lung-associated corticotropin releasing hormone regulation through peripheral CRH and diverse CRH receptor expression by MHC II(+) antigen presenting cells (APCs). We conclude that repeated restraint stress has distinct influences on immune cell populations that appear to be important in the generation of innate and adaptive immune responses along the respiratory tract with the potential to influence local and systemic protection against disease pathogenesis.

Neuroendocrine modulation of signal transducer and activator of transcription-3 in ovarian cancer

There is growing evidence that chronic stress and other behavioral conditions are associated with cancer pathogenesis and progression, but the mechanisms involved in this association are poorly understood. We examined the effects of two mediators of stress, norepinephrine and epinephrine, on the activation of signal transducer and activator of transcription-3 (STAT3), a transcription factor that contributes to many promalignant pathways. Exposure of ovarian cancer cell lines to increasing concentrations of norepinephrine or epinephrine showed that both independently increased levels of phosphorylated STAT3 in a dose-dependent fashion. Immunolocalization and ELISA of nuclear extracts confirmed increased nuclear STAT3 in response to norepinephrine. Activation of STAT3 was inhibited by blockade of the beta1- and beta2-adrenergic receptors with propranolol, and by blocking protein kinase A with KT5720, but not with the alpha receptor blockers prazosin (alpha1) and/or yohimbine (alpha2). Catecholamine-mediated STAT3 activation was not inhibited by pretreatment with an anti-interleukin 6 (IL-6) antibody or with small interfering RNA (siRNA)-mediated decrease in IL-6 or gp130. Regarding the effects of STAT3 activation, exposure to norepinephrine resulted in an increase in invasion and matrix metalloproteinase (MMP-2 and MMP-9) production. These effects were completely blocked by STAT3-targeting siRNA. In mice, treatment with liposome-incorporated siRNA directed against STAT3 significantly reduced isoproterenol-stimulated tumor growth. These studies show IL-6-independent activation of STAT3 by norepinephrine and epinephrine, proceeding through the beta1/beta2-adrenergic receptors and protein kinase A, resulting in increased matrix metalloproteinase production, invasion, and in vivo tumor growth, which can be ameliorated by the down-regulation of STAT3.

Neuroimunomodulação: sobre o diálogo entre os sistemas nervoso e imune

OBJETIVO: Trabalhos de pesquisa provenientes do campo da neuroimunomodulação vêm tornando explícitas as intrincadas relações existentes entre o sistema nervoso central e o sistema imune. Uma revisão bibliográfica foi realizada com o objetivo de descrever as bases de estudo da neuroimunomodulação. MODELOS EXPERIMENTAIS: Sabe-se, hoje, que estados emocionais como ansiedade e depressão são capazes de modificar a atividade do sistema imune como também o fazem o estresse e fármacos com ação no sistema nervoso central. COMPORTAMENTO DOENTIO: Os comportamentos apresentados por um organismo doente devem ser encarados como decorrência de estratégias homeostáticas de cada indivíduo. POSSÍVEIS MECANISMOS DE SINALIZAÇÃO DO SISTEMA IMUNE PARA O SISTEMA NERVOSO CENTRAL: Grande destaque tem sido atribuído para a participação do eixo hipotálamo-pituitária-adrenal, do sistema nervoso autônomo simpático e das citocinas nas sinalizações entre o sistema nervoso central e o sistema imune. CONCLUSÃO: O presente artigo pretende mostrar a relevância dos fenômenos de neuroimunomodulação; ele faz uma análise crítica das influências do sistema nervoso central sobre o sistema imune e vice-versa.

Occupational risk factors for prostate cancer

BACKGROUND

Occupational risk factors for prostate cancer have been investigated with inconsistent findings.

METHODS

This was a population-based case-control study of men in Northeastern Ontario, Canada. Cases (n = 760) were from the Ontario Cancer Registry, 50 to 84 years old, and diagnosed with prostate cancer between 1995 and 1998. Age-frequency matched controls (n = 1,632) were obtained from telephone listings. A questionnaire yielded information on occupational history and self-reported exposures to a list of occupational hazards. Exposures to these hazards were assessed by an occupational hygienist.

RESULTS

An odds ratio estimate (OR) of 1.21 (95 percent confidence interval (% CI) 1.01, 1.46) was found for employment in trades, transport and equipment operators and related occupations, possibly related to exposure to whole-body vibration (OR = 1.38, 95% CI 1.07, 1.78). For the highest quartile of lifetime cumulative workplace physical activity an OR of 1.33 (95% CI 1.02, 1.74) was found. No statistically significant associations were found for any other occupational category or exposure.

CONCLUSIONS

This study does not provide strong evidence for significant occupational risk factors for prostate cancer. However, whole-body vibration exposures, as well as physical activity, may be worth pursuing in future occupational studies.

Social stress, immune functions and disease in rodents

The link between social factors, stress and health has been the focus of many interdisciplinary studies mostly because: (i) animals, including humans, often live in societies; (ii) positive and negative social relationships affect disease and well being; (iii) physiological alterations, which parallel social interactions also modulate immune and neuroendocrine functions. This review will focus on studies conducted on laboratory and wild rodents where social factors such as dyadic interactions, individual housing and differential group housing were investigated. The results obtained allow one to conclude that social factors in rodents are causally linked with immune disorders/disease susceptibility. In particular, lower lymphocyte proliferation and antigen-specific-IgG, granulocytosis and lymphopenia, as well as higher tumor induction and progression, are reliably associated with negative social events. Finally, due to the increasing utilization of social stress-based animal models the reliability of the concept of "social stress" and its evolutionary context are re-evaluated.

Social ecology of children's vulnerability to environmental pollutants

BACKGROUND

The outcomes of exposure to neurotoxic chemicals early in life depend on the properties of both the chemical and the host's environment. When our questions focus on the toxicant, the environmental properties tend to be regarded as marginal and designated as covariates or confounders. Such approaches blur the reality of how the early environment establishes enduring biologic substrates.

OBJECTIVES

In this commentary, we describe another perspective, based on decades of biopsychological research on animals, that shows how the early, even prenatal, environment creates permanent changes in brain structure and chemistry and behavior. Aspects of the early environment-encompassing enrichment, deprivation, and maternal and neonatal stress-all help determine the functional responses later in life that derive from the biologic substrate imparted by that environment. Their effects then become biologically embedded. Human data, particularly those connected to economically disadvantaged populations, yield equivalent conclusions.

DISCUSSION

In this commentary, we argue that treating such environmental conditions as confounders is equivalent to defining genetic differences as confounders, a tactic that laboratory research, such as that based on transgenic manipulations, clearly rejects. The implications extend from laboratory experiments that, implicitly, assume that the early environment can be standardized to risk assessments based on epidemiologic investigations.

CONCLUSIONS

The biologic properties implanted by the early social environment should be regarded as crucial elements of the translation from laboratory research to human health and, in fact, should be incorporated into human health research. The methods for doing so are not clearly defined and present many challenges to investigators.

Preparation of Animals for Research--Issues to Consider for Rodents and Rabbits

This article provides details to consider when preparing to use animals in biomedical research. The stress of transport and receipt of animals into a new environment mandate the need for a period of stabilization and acclimation. This allotment of time often occurs in conjunction with the quarantine period and permits a stress "recovery" period. Discussions in the article include specific effects of the environment on the animal, such as housing and environmental enrichment. Suggestions are offered regarding how to minimize the effects of procedures and equipment through the use of preconditioning techniques. Guidelines for these techniques and for acclimation should be instituted by the institutional animal care and use committee. Stress and distress are placed in perspective as they relate to the preparation of laboratory animals for research.

Racial and ethnic disparities in breast cancer: a multilevel perspective

Although the etiology of racial and ethnic disparities in breast cancer is complex, the studies reviewed here suggest many possible culprits. In the authors' model, outcomes at the cellular level reflect not only genetic constitution and the hormonal milieu but also the interactions of predictors at multiple levels. At the societal level, important predictors include toxin and hormone exposure, access to care, quality of care, and social support. At the individual level, reproductive history, exogenous hormone use, diet,exercise, and response to stress all may influence cellular outcomes. The smooth transition from normal cell function to apoptosis occurs when the interactions between factors at the societal, individual, and cellular levels are harmonious. Perturbations at the societal level, however, such as inferior quality of care, or at the individual level, such as exogenous hormone use,can have profound effects on cell biology and predispose to neoplasia. When these perturbations are systematic and vary by race or ethnicity, disparities in breast cancer incidence and mortality result. Increasing incidence of breast cancer among both men and women likely reflects important trends at the societal and individual levels. These trends may include increased toxin exposure, increased obesity, and changes in the timing and number of births. Efforts to reduce breast cancer incidence and disparities must consider societal and individual factors and the important effects these factors can have on normal cell function.

Psychological stress induces chemoresistance in breast cancer by upregulating mdr1

Psychological distress reduces the efficacy of chemotherapy in breast cancer patients. The mechanism may be related to the altered neuronal or hormonal secretions during stress. Here, we reported that adrenaline, a hormone mediating the biological activities of stress, upregulates mdr1 gene expression in MCF-7 breast cancer cells via alpha(2)-adrenergic receptors in a dose-dependent manner. Mdr1 upregulation can be specifically inhibited by pretreatment with mdr1-siRNA. Consequently, adrenergic stimulation enhances the pump function of P-glycoprotein and confers resistance of MCF-7 cells to paclitaxel. In vivo, restraint stress increases mdr1 gene expression in the MCF-7 cancers that are inoculated subcutaneously into the SCID mice and provokes resistance to doxorubicin in the implanted tumors. The effect can be blocked by injection of yohimbine, an alpha(2)-adrenergic inhibitor, but not by metyrapone, a corticosterone synthesis blocker. Therefore, we conclude that breast cancers may develop resistance against chemotherapeutic drugs under psychological distress by over-expressing mdr1 via adrenergic stimulation.

Origins and evolution of cell phenotypes in breast tumors

This study presents a stochastic model that correlates genomic instability with tumor formation. The model describes the time- and space-variant volumetric concentrations of cancer cells of various phenotypes in a breast tumor. The cells of epithelial origin in the cancerous breast tissue are classified into four different phenotypes, normal epithelial cells and the grade 1, grade 2 and grade 3 cancer cell types with increasing potential for growth and invasion. Equations governing the time course of volumetric concentrations of cell phenotypes are derived by using the principle of conservation of mass. Cell migration into and from the stroma is taken into account. The transformations between cell phenotypes are due to genetic inheritance and chromosome aberrations. These transformations are assumed to be stochastic functions of the local cell concentration. The simulations of the model for planar geometry replicate the shapes of human breast tumors and capture the time history of tumor growth in animal models. Simulations point to transformation of tumor cell population from heterogeneous compositions to a single phenotype at advanced stages of invasive tumors. Systematic variations of model parameters in the computations indicate the important roles the migration capacity, proliferation rate, and phenotype transition probability play in tumor growth. The model developed provides realistic simulations for standard breast cancer therapies and can be used in the optimization studies of chemotherapy, radiotherapy, hormone therapy and emerging individualized therapies for cancer.

Effects of social status and moderate alcohol consumption on mammary gland and endometrium of surgically postmenopausal monkeys

OBJECTIVE

To evaluate the effects of social subordination stress and chronic moderate alcohol consumption on indices of breast and endometrial cancer risk.

DESIGN

Forty-six adult, ovariectomized, cynomolgus monkeys (Macaca fascicularis) were trained to voluntarily drink a placebo or a two-drink/day equivalent of ethanol (0.5 g/kg), 5 days a week for 26 months, the latter resulting in average blood alcohol levels of 42 mg/100 mL. Indices of cell proliferation and sex steroid receptor abundance were measured.

RESULTS

Compared with dominants, socially subordinate females had increased cell proliferation and proportions of glandular (P < 0.02) and epithelial tissue (P = 0.009) and less stroma (P < 0.02) in endometrium, and increased tissue thickness in breast (P < 0.05). There was no evidence of increased risk of breast or endometrial cancer with chronic moderate alcohol consumption, as indicated by markers of cell proliferation and sex steroid receptor abundance. Chronic moderate alcohol consumption did not effect circulating sex steroid concentrations (all P > 0.10). The adipocyte hormones leptin and adiponectin were correlated with indices of cell proliferation and sex steroid receptor abundance.

CONCLUSIONS

These observations suggest that social status was more important than chronic moderate alcohol consumption in endometrial and breast biology of surgically postmenopausal females. Endogenous sex steroid metabolism was not significantly affected by chronic moderate alcohol exposure consistent with the lack of estrogen-like effects on breast and endometrium. Social subordination stress was associated with initial cellular changes that may increase endometrial cancer risk. Ovariectomized cynomolgus monkeys may be a useful model for the study of effects of social factors and obesity on breast and endometrial cancer risk.

The effect of emotional stress on the primary humoral immunity of rats

The effect of exposure to emotional stress on humoral immune function after injection with ovalbumin, a novel antigen, was studied in adult male Wistar rats. Emotional stress was induced by randomly giving empty water bottles to rats trained to drink water at set times. The results showed that emotional stress induced the decrease in spleen weight and specific immunoglobulin G antibody level to ovalbumin, and increased levels of epinephrine, norepinephrine and corticosterone. A decrease of antibody levels correlated negatively with an increase in plasma norepinephrine levels. These findings suggest that emotional stress can modulate immune function, and that sympathetic nervous system may be involved in this immunomodulation.

Individual housing induces altered immuno-endocrine responses to psychological stress in male mice

Social isolation and lack of social support have deleterious effects on health, thus being regarded as one of the most relevant causes of diseases in human and other mammalian species. However, only few are the studies aimed at evaluating the psychoneuroimmunological functions of individually housed subjects. The present study was designed to understand how the behavior and the physiology of male house mice might be affected by individual housing. We first analyzed whether individual housing of different duration (1-42 days) would result in immuno-endocrine dysfunction (experiment 1). Then we investigated whether housing conditions would affect the reaction to an acute mild psychological stress (experiments 2 and 3). There were three main findings: first, individually housing mice for increasing time periods did not induce any major immuno-endocrine effects compared to a stable sibling group housing. Therefore, prolonged isolation does not seem to dramatically impair mice immuno-endocrine functions. Second, when exposed to a mild acute stress, i.e. forced exposure to a novel environment, isolated mice showed higher basal corticosterone and lower type 1 (IL-2) and type 2 (IL-4) cytokines as well as splenocytes proliferation compared to group housed male mice. Finally, when faced with a free choice between a novel environment and their home cage, individually housed mice showed reduced neophobic responses resulting in increased exploration of the novel environment, thus suggesting a low anxiety profile. Altogether, our findings suggest that individual housing in itself does not change immunocompetence and corticosterone level, but does affect reactivity to a stressor. In fact, individually housed mice showed high behavioral arousal, as well as altered immuno-endocrine parameters, when challenged with mild psychological novelty-stress.

Oxidative stress, DNA damage, and breast cancer

Oxidative stress is a disturbance in the balance between the production of reactive oxygen species (ROS) and antioxidant defenses. It occurs when excessive production of ROS overwhelms the antioxidant defense system or when there is a significant decrease or lack of antioxidant defenses. Oxidative stress, in turn, is known to cause DNA damage and mutations of tumor suppressor genes that are critical initial events in carcinogenesis. Interestingly, early findings of the studies suggest that environmental factors, such as high psychological stress and poor nutritional profile (eg, low antioxidant and high fat intake), increase ROS production. Given that breast cancer is a complex disorder in which gene-environment interactions play a significant role in the development of cancer, oxidative stress may be an excellent model for exploring mechanisms mediating gene-environment interactions for nurse scientists and advanced practice nurses. Such investigations may help to suggest future strategies for nonpharmacological interventions for decreasing cancer risk.