Post-cancer fatigue is not associated with immune activation or altered cytokine production

Biological mechanisms of cancer-related fatigue in breast cancer survivors after treatment: a scoping review

PURPOSE

Cancer-related fatigue (CRF) is the most common symptom experienced by cancer survivors. It is a multidimensional symptom affecting physical, emotional, and/or cognitive spheres, different from other types of fatigue. Characteristically is not alleviated by sleep or rest. CRF could have specific features in breast cancer survivors (BCS), because of sex, hormones, and distinct treatments. On the other hand, more than 25% of BCS report persistent CRF for 10 years or more after the diagnosis. The present study aims to recapitulate the knowledge about the biological mechanisms that potentially drive CRF in BCS after treatment.

METHODS

To answer a broad question, a scoping review methodology was used. Data were collated from three bibliographic databases: PubMed, Embase, and Cochrane Central Register of Controlled Trials (CENTRAL). Studies were selected if they had included more than 20 BCS, after finishing their treatment, fatigue was measured with a quantitative scale and biomarkers were analyzed.

RESULTS

The final database was composed of 1896 records. Sixty-four studies finally met the eligibility criteria. Inflammation (61%), hypothalamic-pituitary-adrenal (HPA) axis dysregulation (14%), autonomic nervous system (ANS) dysfunction (11%), and diet (9%) were the biological pathways most frequently studied. Unfortunately, results from studies about inflammation and HPA axis show many inconsistencies.

CONCLUSION

More research about the role of ANS dysfunction and diet on the pathogenesis of CRF would be warranted according to the results of the review. There are some fields such as endocannabinoid systems, mitochondrial dysfunction, gut microbiota, and oxidative stress that have been insufficiently explored.

IMPLICATIONS FOR CANCER SURVIVORS

To widen the scope of future research in the physiopathology of CRF, it is necessary to identify mechanisms that would be potentially involved and have been insufficiently explored. Because of the high prevalence of CRF in BCS and the tremendous impact that fatigue has in their quality of life, it is essential to improve the efficacy of the treatments through a good knowledge of the biological basis of CRF.

Neutralizing interleukin-6 in tumor-bearing mice does not abrogate behavioral fatigue induced by Lewis lung carcinoma

Tumor growth is associated with metabolic reprogramming of various organs including the liver. This metabolic reprogramming is responsible for the development of behavioral fatigue represented by decreased voluntary wheel running in a murine model of lung cancer. To determine whether interleukin (IL-)6 induced by the tumor is responsible for the metabolic reprogramming, mice injected with Lewis lung carcinoma cells in the flank were treated with an anti-mouse IL-6 monoclonal neutralizing antibody using a 2 × 2 factorial design (+/- tumor and +/- anti-IL-6 antibody). Endpoints were represented by behavioral, metabolic and immune phenotypes. Despite its ability to abrogate the increase in plasma levels of IL-6 that was apparent in tumor-bearing mice and decrease inflammatory signaling in the liver, immunoneutralization of IL-6 had no effect on voluntary wheel running and did not modify the tumor-induced alterations in hepatic gene expression of inflammatory cytokines and metabolic factors. These negative results indicate that IL-6 does not mediate the communication between tumor and host in mice implanted with Lewis lung carcinoma.

The IL6-like Cytokine Family: Role and Biomarker Potential in Breast Cancer

IL6-like cytokines are a family of regulators with a complex, pleiotropic role in both the healthy organism, where they regulate immunity and homeostasis, and in different diseases, including cancer. Here we summarise how these cytokines exert their effect through the shared signal transducer IL6ST (gp130) and we review the extensive evidence on the role that different members of this family play in breast cancer. Additionally, we discuss how the different cytokines, their related receptors and downstream effectors, as well as specific polymorphisms in these molecules, can serve as predictive or prognostic biomarkers with the potential for clinical application in breast cancer. Lastly, we also discuss how our increasing understanding of this complex signalling axis presents promising opportunities for the development or repurposing of therapeutic strategies against cancer and, specifically, breast neoplasms.

Genetic associations of fatigue and other symptoms following breast cancer treatment: A prospective study

Background

Cancer-related fatigue, mood disturbances, pain and cognitive disturbance are common after adjuvant cancer therapy, but vary considerably between individuals despite common disease features and treatment exposures. A genetic basis for this variability was explored in a prospective cohort.

Methods

Physical and psychological health of women were assessed prospectively following therapy for early stage breast cancer with self-report questionnaires. Participation in a genetic association sub-study was offered. Indices for the key symptom domains of fatigue, pain, depression, anxiety, and neurocognitive difficulties were empirically derived by principal components analysis from end-treatment questionnaires, and then applied longitudinally. Genetic associations were sought with functional single nucleotide polymorphisms (SNPs) in pro- and anti-inflammatory cytokine genes - tumour necrosis factor (TNF)-α (−308 ​GG), interferon (IFN)-ɣ (+874 ​TA), interleukin (IL)-10 (1082 ​GA and −592 CA), IL-6 (−174 ​GC), IL-1β (−511 ​GA).

Results

Questionnaire data was available for 210 participants, of whom 111 participated in the genetic sub-study. As expected, symptom domain scores generally improved over several months following treatment completion. Tumour and adjuvant treatment related factors were unassociated with either severity or duration of the individual symptom domains, but severity of symptoms at end-treatment was strongly associated with duration for each domain (all p ​< ​0.05). In multivariable analyses, risk genotypes were independently associated with: fatigue with IL-6 -174 ​GG/GC and IL-10 -1082 GG; depression and anxiety with IL-10 -1082 AA; neurocognitive disturbance: TNF-α −308 GG; depression IL-1β (all p ​< ​0.05). The identified SNPs also had cumulative effects in prolonging the time to recovery from the associated symptom domain.

Conclusions

Genetic factors contribute to the severity and duration of common symptom domains after cancer therapy.

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Common symptoms following breast cancer treatment can be grouped into symptom domains.

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Symptom domains are useful to describe patterns and trajectories of symptoms following breast cancer treatment.

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Cytokine gene polymorphisms are associated with the severity and duration of symptom domains following cancer treatment.

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The symptom severity at final treatment predicts the duration of symptoms.

Inflammatory pathway genes associated with inter-individual variability in the trajectories of morning and evening fatigue in patients receiving chemotherapy

Fatigue, a highly prevalent and distressing symptom during chemotherapy (CTX), demonstrates diurnal and interindividual variability in severity. Little is known about the associations between variations in genes involved in inflammatory processes and morning and evening fatigue severity during CTX. The purposes of this study, in a sample of oncology patients (N=543) with breast, gastrointestinal (GI), gynecological (GYN), or lung cancer who received two cycles of CTX, were to determine whether variations in genes involved in inflammatory processes were associated with inter-individual variability in initial levels as well as in the trajectories of morning and evening fatigue. Patients completed the Lee Fatigue Scale to determine morning and evening fatigue severity a total of six times over two cycles of CTX. Using a whole exome array, 309 single nucleotide polymorphisms SNPs among the 64 candidate genes that passed all quality control filters were evaluated using hierarchical linear modeling (HLM). Based on the results of the HLM analyses, the final SNPs were evaluated for their potential impact on protein function using two bioinformational tools. The following inflammatory pathways were represented: chemokines (3 genes); cytokines (12 genes); inflammasome (11 genes); Janus kinase/signal transducers and activators of transcription (JAK/STAT, 10 genes); mitogen-activated protein kinase/jun amino-terminal kinases (MAPK/JNK, 3 genes); nuclear factor-kappa beta (NFkB, 18 genes); and NFkB and MAP/JNK (7 genes). After controlling for self-reported and genomic estimates of race and ethnicity, polymorphisms in six genes from the cytokine (2 genes); inflammasome (2 genes); and NFkB (2 genes) pathways were associated with both morning and evening fatigue. Polymorphisms in six genes from the inflammasome (1 gene); JAK/STAT (1 gene); and NFkB (4 genes) pathways were associated with only morning fatigue. Polymorphisms in three genes from the inflammasome (2 genes) and the NFkB (1 gene) pathways were associated with only evening fatigue. Taken together, these findings add to the growing body of evidence that suggests that morning and evening fatigue are distinct symptoms.

Fatigue is associated with inflammation in patients with head and neck cancer before and after intensity-modulated radiation therapy

Patients with head and neck cancer (HNC) receiving intensity-modulated radiation therapy (IMRT) have particularly high rates of fatigue, and pre- and post-radiotherapy fatigue are prognostic factors for pathologic tumor responses and poor survival. Although inflammation has been proposed as one of the potential mechanisms of fatigue in cancer patients, findings have not been consistent, and there is a dearth of longitudinal studies. Accordingly, we conducted a prospective study in 46 HNC patients pre- and one-month post-IMRT. Fatigue was measured by the Multidimensional Fatigue Inventory (MFI)-20 at both time points along with the assessment of peripheral blood inflammatory markers including interleukin (IL)-6, soluble tumor necrosis factor receptor 2, and C-reactive protein (CRP) and gene expression. Generalized estimating equations were used to examine the association between inflammatory markers and fatigue. Gene enrichment analysis using MetaCore software was performed using up-regulated genes that were significantly associated with IMRT and fatigue. Significant associations between fatigue and IL-6 as well as CRP, which were independent of time, were observed. In addition the change in fatigue from pre- to post-IMRT was positively associated with the change in IL-6 and CRP. Analysis of up-regulated gene transcripts as a function of IMRT and fatigue revealed overrepresentation of transcripts related to the defense response and nuclear factor kappa B. In conclusion, our findings support the hypotheses that inflammation is associated with fatigue over time in HNC patients. Future studies on how inflammation contributes to fatigue as well as strategies targeting inflammation to reduce fatigue are warranted.

Correlations of neutrophil-to-lymphocyte, lymphocyte-to-monocyte and platelet-to-lymphocyte ratios with biomarkers of atherosclerosis risk and inflammatory response in patients with a history of breast cancer

The aim of the present study was to evaluate the correlations of peripheral blood cell count (PBC)-derived ratios with neopterin concentration and biomarkers of atherosclerosis risk in patients with history of breast cancer. Neutrophil-to-lymphocyte ratio (NLR), lymphocyte-to-monocyte ratio (LMR) and platelet-to-lymphocyte ratio (PLR) were calculated in three cohorts of patients with a history of breast cancer and in controls. Significant differences were observed between PBC-derived ratios obtained from automated and manual counts. NLR and PLR were significantly higher and LMR was significantly lower in patients. NLR and PLR correlated positively with each other and negatively with LMR. NLR exhibited a significant correlation with age, glucose and C-reactive protein (CRP) concentrations, whereas LMR correlated negatively with CRP. With the exception of a correlation between LMR and urinary or serum neopterin concentrations in controls, no other correlation between neopterin concentrations and PBC-derived ratios was observed. NLR ≥3 was a significant predictor of poor survival, but neither urinary neopterin ≥205 μmol/mol creatinine, NLR ≥150 nor LMR ≥4.25 was significantly associated with survival. In conclusion, no consistent correlation was observed between urinary and serum neopterin concentrations and any of the PBC-derived ratios. In a cohort of breast cancer patients, a higher NLR predicted poor survival.

Preliminary differences in peripheral immune markers and brain metabolites between fatigued and non-fatigued breast cancer survivors: a pilot study

Persistent cancer-related fatigue (PCRF) is one of the most troubling side-effects of breast cancer (BC) treatment. One explanatory model for PCRF is sickness behavior, which is a set of adaptive responses including sleepiness and depressed mood in reaction to an inflammatory trigger. Prior research has investigated differences in inflammatory cytokines between fatigued and non-fatigued BC survivors, but no study has examined differences in brain metabolites. Differences in inflammatory markers, and brain metabolites using proton magnetic resonance spectroscopy were evaluated within 16 fatigued and 13 non-fatigued BC survivors. Fatigued BC survivors had significantly higher ratios of two markers derived from brain metabolites; namely (a) creatine, normalized to total creatine (creatine + phosphocreatine (Cr/tCr)) ratio (P = 0.03) and (b) glutamate + glutamine (Glx) to N-acetyl-aspartate (NAA) ratio (P = 0.01) in the posterior insula compared to non-fatigued breast cancer survivor. Further, serum IL-6 was increased in fatigued women compared to non-fatigued women (P = 0.03), Using receiver operator curves (ROC) we determined that the posterior insula Glx/NAA ratio was the best predictor of fatigue with an overall area under the receiver operating characteristic curve (AUROC) of 79%, with a sensitivity of 81% and a specificity of 69%. However, posterior insula Glx/NAA, Cr/tCr and serum IL-6 were not significantly correlated with one another implying the possibility of independent biological mechanisms for PCRF rather than an interrelated mechanism as represented by the sickness behavior model. This study provides novel preliminary evidence of several distinct neurobiological changes in the posterior insula associated with PCRF in BC survivors. Future, longitudinal studies are needed to explore these distinct biological phenomena where changes through time in peripheral immune markers and brain metabolites are examined to determine if they correlate with changes in fatigue.

Associations between multiple chronic conditions and cancer-related fatigue: an integrative review

PROBLEM IDENTIFICATION

To summarize the current state of nursing knowledge related to the association of multiple chronic conditions (MCCs) and cancer-related fatigue (CRF) in patients with solid tumors during chemotherapy.

LITERATURE SEARCH

A systematic literature search of PubMed, CINAHL®, EMBASE, Cochrane, and ProQuest Dissertations and Theses for primary nursing research from January 2000 to June 2012 that examined the prevalence and/or severity of CRF with MCCs or a single comorbidity.Data Evaluation: The studies were appraised for the clarity and focus of the research question and the appropriateness of the method and research design. A 13-item quality criteria checklist evaluated the data from each article on a 0-2 scale (0 = poor, 1 = fair, 2 = good).

DATA ANALYSIS

Of 329 abstracts, 21 studies were included in the analysis. The association of MCC and CRF was mostly reported in aggregate, with a mean of three MCCs per patient.Presentation of Findings: Having one or more other comorbidities was significantly associated with the prevalence and severity of CRF. Specifically, arthritis, hypertension, and cardiac disease, although not consistently or clinically defined across studies, are associated with an increased prevalence and severity of CRF. The association of MCC and CRF prevalence and severity was inconsistent because of the variability in the measures used and the time span identified to measure changes.

IMPLICATIONS FOR NURSING PRACTICE

Awareness of the prevalence of MCCs is essential to support patients experiencing CRF. Holistic nursing assessment of the patient's symptoms-with an awareness of MCCs-would help improve symptom management to limit the effect of CRF.

The representation of inflammatory signals in the brain - a model for subjective fatigue in multiple sclerosis

In multiple sclerosis (MS) patients, fatigue is rated as one of the most common and disabling symptoms. However, the pathophysiology underlying this fatigue is not yet clear. Several lines of evidence suggest that immunological factors, such as elevated levels of pro-inflammatory cytokines, may contribute to subjective fatigue in MS patients. Pro-inflammatory cytokines represent primary mediators of immune-to-brain-communication, modulating changes in the neurophysiology of the central nervous system. Recently, we proposed a model arguing that fatigue in MS patients is a subjective feeling, which is related to inflammation. Moreover, it implies that fatigue can be measured behaviorally only by applying specific cognitive tasks related to alertness and vigilance. In the present review, we focus on the subjective feeling of MS-related fatigue. We examine the hypothesis that the subjective feeling of MS-related fatigue may be a variant of inflammation-induced sickness behavior, resulting from cytokine-mediated activity changes within brain areas involved in interoception and homeostasis including the insula, the anterior cingulate, and the hypothalamus. We first present studies demonstrating a relationship between pro-inflammatory cytokines and subjective fatigue in healthy individuals, in people with inflammatory disorders, and particularly in MS patients. Subsequently, we discuss studies analyzing the impact of anti-inflammatory treatment on fatigue. In the next part of this review, we present studies on the transmission and neural representation of inflammatory signals, with a special focus on possible neural concomitants of inflammation-induced fatigue. We also present two of our studies on the relationship between local gray and white matter atrophy and fatigue in MS patients. Finally, we discuss some implications of our findings and future perspectives.

Cytokine polymorphisms are associated with fatigue in adults living with HIV/AIDS

Fatigue has been associated with inflammation and cytokine activity among adults, but this relationship has not been evaluated among adults living with HIV. Diurnal patterns of fatigue have been previously identified in adults with HIV/AIDS. Thus, the purpose of this study was to describe these fatigue patterns in relation to cytokine plasma concentrations and gene polymorphisms. A convenience sample of 317 adults living with HIV/AIDS completed a measure of fatigue in the morning and evening for three consecutive days; participants reporting low levels of both morning and evening fatigue (n=110) or high levels of fatigue in the morning and evening (n=114) were included in the analysis, resulting in a final sample of 224 adults (151 men, 55 women, and 18 transgender). Plasma cytokines were analyzed, and genotyping was conducted for 15 candidate genes involved in cytokine signaling: interferon-gamma (IFNG), IFNG receptor 1 (IFNGR1), interleukins (IL), nuclear factor of kappa light polypeptide gene enhancer in B cells (NFKB-1 and -2), and tumor necrosis factor alpha (TNFA). Demographic and clinical variables were evaluated as potential covariates. Controlling for genomic estimates of ancestry and self-reported race/ethnicity and gender, the high fatigue pattern was associated with five single nucleotide polymorphisms (SNPs): IL1B rs1071676 and rs1143627, IL4 rs2243274, and TNFA rs1800683 and rs1041981. The IL1B and TNFA polymorphisms were not associated with plasma levels of IL-1β or TNFα, respectively. This study strengthens the evidence for an association between inflammation and fatigue. In this chronic illness population, the cytokine polymorphisms associated with high levels of morning and evening fatigue provide direction for future personalized medicine intervention research.

Characterization of fatigue states in medicine and psychiatry by structured interview

CONTEXT

Unexplained fatigue states are prevalent, with uncertain diagnostic boundaries.

OBJECTIVE

Patients with fatigue-related illnesses were investigated by questionnaire and a novel semistructured interview to identify discriminatory features.

METHODS

Cross-sectional samples of women from specialist practices with chronic fatigue syndrome (n = 20), postcancer fatigue (PCF; n = 20), or major depression (n = 16) were recruited. Additionally, two longitudinal samples were studied: women with fatigue associated with acute infection who subsequently developed postinfective fatigue syndrome (n = 20) or recovered uneventfully (n = 21), and women undergoing adjuvant therapy for breast cancer experiencing treatment-related fatigue who subsequently developed PCF (n = 16) or recovered uneventfully (n = 16). Patients completed self-report questionnaires, and trained interviewers applied the Semi-structured Clinical Interview for Neurasthenia. The receiver operating characteristics curves of the interview were measured against clinician-designated diagnoses. Cluster analyses were performed to empirically partition participants by symptom characteristics.

RESULTS

The interview had good internal consistency (Cronbach alpha "fatigue" = .83), and diagnostic sensitivity and specificity for chronic fatigue syndrome (100% and 83%) and major depression (100% and 72%), with reasonable parameters for PCF (72% and 58%). Empirical clustering by "fatigue" or "neurocognitive difficulties" items allocated most patients to one group, whereas "mood disturbance" items correctly classified patients with depression only.

CONCLUSIONS

The Semi-structured Clinical Interview for Neurasthenia offers reliable diagnostic use in assessing fatigue-related conditions. The symptom domains of fatigue and neurocognitive difficulties are shared across medical and psychiatric boundaries, whereas symptoms of depression such as anhedonia are distinguishing.

Differing leukocyte gene expression profiles associated with fatigue in patients with prostate cancer versus chronic fatigue syndrome

BACKGROUND

Androgen deprivation therapy (ADT) often worsens fatigue in patients with prostate cancer, producing symptoms similar to chronic fatigue syndrome (CFS). Comparing expression (mRNA) of many fatigue-related genes in patients with ADT-treated prostate cancer versus with CFS versus healthy controls, and correlating mRNA with fatigue severity may clarify the differing pathways underlying fatigue in these conditions.

METHODS

Quantitative real-time PCR was performed on leukocytes from 30 fatigued, ADT-treated prostate cancer patients (PCF), 39 patients with CFS and 22 controls aged 40-79, together with ratings of fatigue and pain severity. 46 genes from these pathways were included: (1) adrenergic/monoamine/neuropeptides, (2) immune, (3) metabolite-detecting, (4) mitochondrial/energy, (5) transcription factors.

RESULTS

PCF patients showed higher expression than controls or CFS of 2 immune transcription genes (NR3C1 and TLR4), chemokine CXCR4, and mitochondrial gene SOD2. They showed lower expression of 2 vasodilation-related genes (ADRB2 and VIPR2), 2 cytokines (TNF and LTA), and 2 metabolite-detecting receptors (ASIC3 and P2RX7). CFS patients showed higher P2RX7 and lower HSPA2 versus controls and PCF. Correlations with fatigue severity were similar in PCF and CFS for only DBI, the GABA-A receptor modulator (r=-0.50, p<0.005 and r=-0.34, p<0.05). Purinergic P2RY1 was correlated only with PCF fatigue and pain severity (r=+0.43 and +0.59, p=0.025 and p=0.001).

CONCLUSIONS

PCF patients differed from controls and CFS in mean expression of 10 genes from all 5 pathways. Correlations with fatigue severity implicated DBI for both patient groups and P2RY1 for PCF only. These pathways may provide new targets for interventions to reduce fatigue.

C-reactive protein predicts fatigue independently of depression in breast cancer patients prior to chemotherapy

Heightened inflammatory activity has been proposed as a mechanism for the development of cancer-related fatigue (CRF), a common and distressing condition that can negatively affect quality of life. Inflammation is also implicated in the pathogenesis of depression, and depression is a strong predictor of CRF. Thus, the role of the pro-inflammatory cytokine network in CRF may be mediated by depression or both conditions may share similar underlying physiological processes. The current study investigated associations between fatigue, depression and inflammatory cytokine (IFN-γ, IL-6, TNF-α) and CRP concentrations, as well as kynurenine pathway (KP) activation, in 61 breast cancer patients prior to chemotherapy. Changes in inflammatory markers and KP activation over time were also explored, and associations with changes in fatigue and depression were examined. Higher levels of CRP were significantly correlated with fatigue and depression before chemotherapy; nevertheless, CRP predicted fatigue independently of depression. Although greater kynurenine concentrations were associated with increased immune activation, there was no evidence that the KP played a role in fatigue or depression. Furthermore, no relationships emerged between either fatigue or depression and IFN-γ, IL-6, or TNF-α before chemotherapy. Nevertheless, kynurenine levels pre- and post-treatment significantly predicted changes in depression, suggesting that heightened KP activation may contribute to depressive symptoms in patients treated for cancer. In addition, IL-6 significantly covaried with fatigue. These preliminary findings provide some support for the idea that low-grade inflammation contributes to the development of CRF, independently of depression; however, there was no evidence that this is mediated by KP activity.

Serum cytokines and chronic fatigue in adults surviving after childhood leukemia and lymphoma

INTRODUCTION

Fatigue is a common and distressing symptom in all phases of the cancer trajectory. Chronic fatigue (CF) is defined as fatigue with duration ⩾6months. The etiology of CF in cancer survivors is poorly understood, but a link to inflammatory activity has been suggested. In the present study we explored the relation between CF and the levels of 17 cytokines among a national representative sample of 232 adult survivors after childhood lymphoma and acute lymphoblastic leukemia (ALL).

METHODS

Chalder's fatigue questionnaire assessed CF. The sera of the survivors were analyzed for 27 cytokines, where of 17 were detectable.

RESULTS

Median age at survey and diagnosis was 29.7years (range 18.6-54.5years) and 9.6years (range 0.3-18.0years), respectively. Median follow-up time was 21.5years (range 7.1-40.0years). CF was not associated with increased levels of any of the 17 detectable cytokines when all three diagnostic groups were included in the analyses. In sub-analyses of the non-Hodgkin lymphoma survivors only, those with CF had significant higher levels of IL-9, FGF, PDGF and eotaxin compared to those without CF (p<0.05). Gender, age, diagnosis, obesity, or reduced heart function did not impact upon the results. Differences in cytokine levels between the diagnostic groups were observed irrespective of the presence/absence of CF.

CONCLUSION

This study could not confirm a relation between levels of cytokines and CF in adults who survived childhood lymphoma and ALL, except for among NHL survivors. Despite the broad spectrum of cytokines and relatively large sample, small aberrances may not have been traced.

The role of intratumoral and systemic IL-6 in breast cancer

Chronic low-grade inflammation plays an important role in the pathogenesis of several cancer forms including breast cancer. The pleiotropic cytokine IL-6 is a key player in systemic inflammation, regulating both the inflammatory response and tissue metabolism during acute stimulations. Here, we review the associations between IL-6 and breast cancer ranging from in vitro cell culture studies to clinical studies, covering the role of IL-6 in controlling breast cancer cell growth, regulation of cancer stem cell renewal, as well as breast cancer cell migration. Moreover, associations between circulating IL-6 and risk of breast cancer, prognosis for patients with prevalent disease, adverse effects and interventions to control systemic IL-6 levels in patients are discussed. In summary, direct application of IL-6 on breast cancer cells inhibits proliferation in estrogen receptor positive cells, while high circulating IL-6 levels are correlated with a poor prognosis in breast cancer patients. This discrepancy reflects distinct roles of IL-6, with elevated systemic levels being a biomarker for tumor burden, physical inactivity, and impaired metabolism, while local intratumoral IL-6 signaling is important for controlling breast cancer cell growth, metastasis, and self renewal of cancer stem cells.