Inflammation and increased aromatase expression occur in the breast tissue of obese women with breast cancer

Nuclear receptors as modulators of the tumor microenvironment

Over the past several decades of cancer research, the inherent complexity of tumors has become increasingly appreciated. In addition to acquired cell-intrinsic properties, tumor initiation and growth is supported by an abundance of parenchymal, inflammatory, and stromal cell types, which infiltrate and surround the tumor. Accumulating evidence shows that numerous components of this supportive milieu, referred to collectively as the tumor microenvironment, are indeed critical during the process of multistep tumorigenesis. These findings highlight the important interplay between neoplastic cells and tumor-associated cell types, and suggest that therapy should target both neoplastic cells and supportive stromal cells to effectively attenuate tumor growth. The nuclear receptor superfamily encompasses a druggable class of molecules expressed in numerous stromal and parenchymal cell types, whose established physiologic roles suggest their potential as therapeutic and preventive targets in the context of the reactive tumor microenvironment. In this minireview, we discuss recent evidence that tumor-associated inflammation, angiogenesis, and fibrosis can be modulated at the transcriptional level by nuclear receptors and their ligands. As these processes have been widely implicated in cancer initiation, progression, and resistance to current therapy, nuclear receptor ligands targeting the tumor microenvironment may be potent antitumor agents in combination therapies, including for preventing cancer development within high-risk populations.

Molecular mechanisms of cancer development in obesity

The increasing incidence of obesity and its co-morbid conditions poses a great challenge to global health. In addition to cardiovascular disease and diabetes, epidemiological data demonstrate a link between obesity and multiple types of cancer. The molecular mechanisms underlying how obesity causes an increased risk of cancer are poorly understood. Obesity disrupts the dynamic role of the adipocyte in energy homeostasis, resulting in inflammation and alteration of adipokine (for example, leptin and adiponectin) signalling. Additionally, obesity causes secondary changes that are related to insulin signalling and lipid deregulation that may also foster cancer development. Understanding these molecular links may provide an avenue for preventive and therapeutic strategies to reduce cancer risk and mortality in an increasingly obese population.

Normal breast tissue of obese women is enriched for macrophage markers and macrophage-associated gene expression

Activation of inflammatory pathways is one plausible mechanism underlying the association between obesity and increased breast cancer risk. However, macrophage infiltration and local biomarkers of inflammation in breast adipose tissue have seldom been studied in association with obesity. Gene expression profiles of normal breast tissue from reduction mammoplasty patients were evaluated by whole genome microarrays to identify patterns associated with obesity status (normal-weight, body mass index (BMI) <25; overweight, BMI 25-29.9; obese, BMI ≥30). The presence of macrophage-enriched inflammatory loci with immunopositivity for CD68 protein was evaluated by immunohistochemistry (IHC). After adjusting for confounding by age, 760 genes were differentially expressed (203 up and 557 down; FDR = 0.026) between normal-weight and obese women. Gene ontology analysis suggested significant enrichment for pathways involving IL-6, IL-8, CCR5 signaling in macrophages and RXRα and PPARα activation, consistent with a pro-inflammatory state and suggestive of macrophage infiltration. Gene set enrichment analysis also demonstrated that the genomic signatures of monocytes and macrophages were over-represented in the obese group with FDR of 0.08 and 0.13, respectively. Increased macrophage infiltration was confirmed by IHC, which showed that the breast adipose tissue of obese women had higher average macrophage counts (mean = 8.96 vs. 3.56 in normal-weight women) and inflammatory foci counts (mean = 4.91 vs. 2.67 in normal-weight women). Obesity is associated with local inflammation and macrophage infiltration in normal human breast adipose tissues. Given the role of macrophages in carcinogenesis, these findings have important implications for breast cancer etiology and progression.

Inflammatory marker changes in a yearlong randomized exercise intervention trial among postmenopausal women

Chronic low-grade inflammation is a possible risk factor for cancer that may be modifiable with long-term exercise. Very few randomized controlled trials (RCT) have studied the isolated effects of exercise on low-grade inflammation exclusively in postmenopausal women. The Alberta Physical Activity and Breast Cancer Prevention Trial, a 2-armed RCT in healthy postmenopausal women, examined how 1 year of moderate to vigorous aerobic exercise, compared with usual inactivity, influenced circulating inflammatory markers. Baseline, 6-month, and 12-month serum was analyzed by direct chemiluminescent immunoassays to measure high sensitivity C-reactive protein (CRP) and ELISAs to measure interleukin 6 (IL-6) and TNF-α. Intention to treat analyses were conducted with linear mixed models. Statistically significant differences in CRP were observed over 12 months for exercisers versus controls (treatment effect ratio = 0.87, 95% CI = 0.79-0.96, P = 0.005), but not in IL-6 or TNF-α. A statistically significant trend (P(trend) = 0.021) of decreasing CRP with increasing exercise adherence and stronger intervention effects on CRP in women with higher baseline physical fitness (P(heterogeneity) = 0.040) was found. The intervention effect on CRP became statistically nonsignificant with adjustment for dietary fiber intake change and seemed to be mediated by fat loss. Low-grade inflammation may be lowered with exercise, but confounding by dietary intake occurred and should be considered in future studies. Further trials are needed to corroborate our findings about the optimal dose of exercise required to lower CRP levels and effect modification of CRP changes by levels of body fatness and fitness.

Sex steroid hormone levels in breast adipose tissue and serum in postmenopausal women

Elevated levels of circulating estrogens and androgens are linked to higher breast cancer risk among postmenopausal women; however, little is known about hormone levels within the breast. Hormone concentrations within the breast may not be reflected in the blood and are likely important contributors to breast carcinogenesis. We used a previously validated method to measure levels of estrone, estradiol, androstenedione, and testosterone in adipose tissue removed as part of breast excisions performed for cancer in 100 postmenopausal women (69 ER/PR +/+ and 31 ER/PR -/-) participating in a breast cancer case-control study. We also measured the same steroid hormones, as well as estrone sulfate, and sex hormone-binding globulin (SHBG) in serum from these patients and 100 controls matched on ages at blood collection and on menopause. Overall, concentrations of serum hormones did not vary significantly between controls and cases. However, women with ER-/PR- breast cancers had lower circulating levels of all measured sex steroid hormones and higher SHBG levels than women with ER+/PR+ breast cancers and controls. Similarly, hormone concentrations in breast adipose tissue were higher among women with ER+/PR+ compared to ER-/PR- breast cancer, although differences were only significant for testosterone. These data demonstrate that high sex steroid concentrations in both serum and adipose tissues are more strongly related to ER+/PR+ than ER-/PR- breast cancers. Measurement of sex hormones in serum and in the microenvironment may help in understanding the hormonal etiology of breast cancer, suggest methods for prevention, and have value in gauging treatment response and prognosis.