Diabetes, metformin, and breast cancer in postmenopausal women

CARING (CAncer Risk and INsulin analoGues): the association of diabetes mellitus and cancer risk with focus on possible determinants - a systematic review and a meta-analysis

Background:

Patients suffering from diabetes mellitus (DM) may experience an increased risk of cancer; however, it is not certain whether this effect is due to diabetes per se.

Objective:

To examine the association between DM and cancers by a systematic review and meta-analysis according to the PRISMA guidelines.

Data Sources:

The systematic literature search includes Medline at PubMed, Embase, Cinahl, Bibliotek.dk, Cochrane library, Web of Science and SveMed+ with the search terms: “Diabetes mellitus”, “Neoplasms”, and “Risk of cancer”.

Study Eligibility Criteria:

The included studies compared the risk of cancer in diabetic patients versus non-diabetic patients. All types of observational study designs were included.

Results:

Diabetes patients were at a substantially increased risk of liver (RR=2.1), and pancreas (RR=2.2) cancer. Modestly elevated significant risks were also found for ovary (RR=1.2), breast (RR=1.1), cervix (RR=1.3), endometrial (RR=1.4), several digestive tract (RR=1.1-1.5), kidney (RR=1.4), and bladder cancer (RR=1.1). The findings were similar for men and women, and unrelated to study design. Meta-regression analyses showed limited effect modification of body mass index, and possible effect modification of age, gender, with some influence of study characteristics (population source, cancer- and diabetes ascertainment).

Limitations:

Publication bias seemed to be present. Only published data were used in the analyses.

Conclusions:

The systematic review and meta-analysis confirm the previous results of increased cancer risk in diabetes and extend this to additional cancer sites. Physicians in contact with patients with diabetes should be aware that diabetes patients are at an increased risk of cancer.

Metformin decreases circulating androgen and estrogen levels in nondiabetic women with breast cancer

INTRODUCTION

Diabetic patients treated with metformin have a lower risk of developing BC or a better BC prognosis. Metformin might reduce cancer growth through direct antiproliferative effects or through indirect mechanisms, particularly the reduction of insulin. In a randomized study on nondiabetic BC patients in natural menopause with high testosterone levels, we observed a significant decrease in insulin and in testosterone levels with metformin 1500 mg/d compared with 1000 mg/d. We present the results of a new analysis of our study on the effect of metformin on the bioavailability of sex hormones.

PATIENTS AND METHODS

One hundred twenty-four eligible women were initially invited to take metformin 500 mg/d for 3 months. The 108 women who completed the first 3 months continued the study using 1000 mg/d for 1 month. The women were then randomized into 2 groups, and, for the subsequent 5 months, 1 group increased the dose to 1500 mg/d, and the other group continued with 1000 mg/d.

RESULTS

Ninety-six women completed the study, 43 receiving metformin 1500 mg/day, and 53 receiving 1000 mg/day. The women receiving 1500 mg/d showed a greater and significant reduction of free testosterone (-29%) and estradiol (-38%), a borderline significant reduction of estrone and insulin-like growth factor-1, and a nonsignificant reduction of androstenedione. They also showed a nonsignificant increase of dehydroepiandrosterone sulfate.

CONCLUSION

Metformin does not interfere with the production of dehydroepiandrosterone sulfate. Besides, it decreases estradiol levels, basically through the reduction of testosterone. These hormonal changes might have clinical relevance.

Metformin and cancer risk and mortality: a systematic review and meta-analysis taking into account biases and confounders

Treatment of diabetics with metformin is associated with decreased breast cancer risk in observational studies, but it remains unclear if this drug has clinical antineoplastic activity. In a recent presurgical trial, we found a heterogeneous effect of metformin on breast cancer proliferation (ki-67) depending upon insulin resistance (HOMA index). Here, we determined the associations of additional serum biomarkers of insulin resistance, tumor subtype, and drug concentration with ki-67 response to metformin. Two-hundred non-diabetic women were randomly allocated to metformin (850 mg/bid) or placebo for 4 weeks prior to breast cancer surgery. The ki-67 response to metformin was assessed comparing data obtained from baseline biopsy (ki-67 and tumor subtype) and serum markers (HOMA index, C-peptide, IGF-I, IGFBP-1, IGFBP-3, free IGF-I, hs-CRP, adiponectin) with the same measurements at definitive surgery. For patients with a blood sample taken within 24 h from last drug intake, metformin level was measured. Compared with placebo, metformin significantly decreased ki-67 in women with HOMA > 2.8, those in the lowest IGFBP-1 quintile, those in the highest IGFBP-3 quartile, those with low free IGF-I, those in the top hs-CRP tertile, and those with HER2-positive tumors. In women with HOMA index > 2.8, drug levels were positively correlated with the ki-67 decrease, whereas no trend was noted in women with HOMA < 2.8 (p-interaction = 0.07). At conventional antidiabetic doses, the effect of metformin on tumor ki-67 of non-diabetic breast cancer patients varies with host and tumor characteristics. These findings are relevant to design breast cancer prevention and treatment trials with metformin.

Metformin and cancer risk and mortality: a systematic review and meta-analysis taking into account biases and confounders

Previous meta-analyses have shown that the antidiabetic agent metformin is associated with reduced cancer incidence and mortality. However, this effect has not been consistently demonstrated in animal models and recent epidemiologic studies. We performed a meta-analysis with a focus on confounders and biases, including body mass index (BMI), study type, and time-related biases. We identified 71 articles published between January 1, 1966, and May 31, 2013, through Pubmed, ISI Web of Science (Science Citation Index Expanded), Embase, and the Cochrane library that were related to metformin and cancer incidence or mortality. Study characteristics and outcomes were abstracted for each study that met inclusion criteria. We included estimates from 47 independent studies and 65,540 cancer cases in patients with diabetes. Overall cancer incidence was reduced by 31% [summary relative risk (SRR), 0.69; 95% confidence interval (CI), 0.52-0.90], although between-study heterogeneity was considerable (I(2) = 88%). Cancer mortality was reduced by 34% (SRR, 0.66; 95% CI, 0.54-0.81; I(2) = 21%). BMI-adjusted studies and studies without time-related biases also showed significant reduction in cancer incidence (SRR, 0.82; 95% CI, 0.70-0.96 with I(2) = 76% and SRR, 0.90; 95% CI, 0.89-0.91 with I(2) = 56%, respectively), albeit with lesser magnitude (18% and 10% reduction, respectively). However, studies of cancer mortality and individual organ sites did not consistently show significant reductions across all types of analyses. Although these associations may not be causal, our results show that metformin may reduce cancer incidence and mortality in patients with diabetes However, the reduction seems to be of modest magnitude and not affecting all populations equally. Clinical trials are needed to determine if these observations apply to nondiabetic populations and to specific organ sites.

The effect of metformin on breast cancer outcomes in patients with type 2 diabetes

Observational data suggest that metformin use decreases breast cancer (BC) incidence in women with diabetes; the impact of metformin on BC outcomes in this population is less clear. The purpose of this analysis was to explore whether metformin use influences BC outcomes in women with type 2 diabetes. Prospective institutional databases were reviewed to identify patients with diabetes who received chemotherapy for stages I–III BC from 2000 to 2005. Patients diagnosed with diabetes before or within 6 months of BC diagnosis were included. Males and those with type I, gestational, or steroid-induced diabetes were excluded. Patients were stratified based on metformin use, at baseline, defined as use at time of BC diagnosis or at diabetes diagnosis if within 6 months of BC diagnosis. Kaplan–Meier methods were used to estimate rates of recurrence-free survival (RFS), overall survival (OS), and contralateral breast cancer (CBC). We identified 313 patients with diabetes who received chemotherapy for BC, 141 (45%) fulfilled inclusion criteria and 76 (54%) used metformin at baseline. There were no differences in clinical presentation or tumor characteristics between metformin users and nonusers. At a median follow-up of 87 months (range, 6.9–140.4 months), there was no difference in RFS (P = 0.61), OS (P = 0.462), or CBC (P = 0.156) based on metformin use. Five-year RFS was 90.4% (95% CI, 84–97) in metformin users and 85.4% (95% CI, 78–94) in nonusers. In this cohort of patients with type 2 diabetes receiving systemic chemotherapy for invasive BC, the use of metformin was not associated with improved outcomes.

Adherence to oral diabetes medications and glycemic control during and following breast cancer treatment

OBJECTIVES

We evaluated changes in oral diabetes mellitus medication adherence and persistence, as well as glycemic control for the year prior to breast cancer (BC) diagnosis (Year -1), during BC treatment, and in subsequent years.

METHODS

Cohort study of 4216 women diagnosed with incident early stage (I and II) invasive BC from 1990-2008, enrolled in Group Health Cooperative. Adherence was measured in prevalent users at baseline (N = 509), during treatment, and 1-3 years post-diagnosis using medication possession ratio (MPR), % adherent (MPR ≥0.80) and discontinuation rates. Laboratory data on glycosylated hemoglobin (HbA1c ) was obtained for the corresponding periods.

RESULTS

Compared with Year -1, mean MPR for metformin/sulfonylureas (0.86 vs 0.49, p < 0.001) and % adherent (75.3% vs 24.6%, p < 0.001) declined during BC treatment. MPR and % adherent rose slightly during Years 1-3 post-diagnosis but never returned to baseline. Discontinuation rates increased from treatment to Year +1 (59.3% vs 75.6%, p < 0.001) and remained elevated during subsequent observation periods. Compared with baseline, increased HbA1c (7.0% vs 7.4%, p = 0.001) and % women with high HbA1c >7.0% (34.9% vs 51.1%, p < 0.001) coincided with decreased adherence.

CONCLUSION

Diabetes mellitus medication adherence declined following BC diagnosis, whereas discontinuation rates were relatively stable but poor overall. The proportion of adherent users increased only marginally following treatment, whereas the proportion of women meeting goals for HbA1c decreased considerably. These data support the hypothesis that adherence and subsequent glycemic control are sensitive to BC diagnosis and treatment. Confirmatory studies in other settings, on reasons for reduced adherence post-cancer diagnosis, and on subsequent indicators of glycemic control are warranted.

Aggressive estrogen-receptor-positive breast cancer arising in patients with elevated body mass index

BACKGROUND

Obese women with estrogen receptor (ER)-positive breast cancer may experience worse disease-free and overall survival. We hypothesize that this observation is due to intrinsically aggressive disease and that obesity will be associated with higher histologic grade and Ki67.

METHODS

A sequential cohort of women with breast cancer diagnosed over 2 years was assembled from institutional tumor registries. Patient and tumor characteristics were abstracted from medical records; those with non-invasive tumors, or lacking body mass index (BMI), Ki67 or histologic grade data, were excluded. Univariate and multivariate analysis was performed to investigate the relationship between markers of aggressive disease (grade and Ki67) and multiple variables associated with obesity. A subgroup analysis was performed to investigate further whether ER and menopausal status influenced associations between BMI and aggressive phenotypes.

RESULTS

Of the 1007 patients initially identified, 668 (68 %) met the eligibility criteria. In univariate analysis, histologic grade and Ki67 were strongly associated with increased BMI, younger age, and African-American race, but less so with diabetes, hypertension, and hyperlipidemia. Multivariate analysis confirmed that higher histologic grade was associated with increased BMI (p = 0.02), and that increased Ki67 was associated with younger age (p = 0.0003) and African-American race (p = 0.002). Additional analysis found that the association between increased BMI and higher-grade tumors was particularly significant in premenopausal women with ER-positive disease.

CONCLUSION

This study concludes that increased BMI is associated with aggressive-phenotype breast cancer and may be particularly relevant to ER-positive breast cancer developing in premenopausal African-American women.

The quality control theory of aging

The quality control (QC) theory of aging is based on the concept that aging is the result of a reduction in QC of cellular systems designed to maintain lifelong homeostasis. Four QC systems associated with aging are 1) inadequate protein processing in a distressed endoplasmic reticulum (ER); 2) histone deacetylase (HDAC) processing of genomic histones and gene silencing; 3) suppressed AMPK nutrient sensing with inefficient energy utilization and excessive fat accumulation; and 4) beta-adrenergic receptor (BAR) signaling and environmental and emotional stress. Reprogramming these systems to maintain efficiency and prevent aging would be a rational strategy for increased lifespan and improved health. The QC theory can be tested with a pharmacological approach using three well-known and safe, FDA-approved drugs: 1) phenyl butyric acid, a chemical chaperone that enhances ER function and is also an HDAC inhibitor, 2) metformin, which activates AMPK and is used to treat type 2 diabetes, and 3) propranolol, a beta blocker which inhibits BAR signaling and is used to treat hypertension and anxiety. A critical aspect of the QC theory, then, is that aging is associated with multiple cellular systems that can be targeted with drug combinations more effectively than with single drugs. But more importantly, these drug combinations will effectively prevent, delay, or reverse chronic diseases of aging that impose such a tremendous health burden on our society.

Current strategies for the prevention of breast cancer

Due to the high incidence of breast cancer in the United States, optimal strategies for its prevention are imperative. This entails identification of women who are at an increased risk for breast cancer and an integrative approach that includes effective screening methods as well as nutritional, pharmacologic, and surgical management. Several breast cancer risk-assessment tools, such as the Gail and Claus models, can help clinicians determine the quantitative risk of breast cancer. The role of selective estrogen receptor modulators, such as tamoxifen and raloxifene, for the prevention of breast cancer has been well established. Several other agents, such as aromatase inhibitors, are currently being investigated. The potential adverse effects of these chemopreventive agents, which include an impact on the quality of life, must be discussed with the patient before deciding on this approach. Additionally, breast cancer risk factors have been identified over the years; some of them are modifiable, but others are not. Although there is no conclusive evidence to suggest the protective role of specific dietary components, alcohol consumption and obesity are associated with an increased breast cancer risk; thus lifestyle changes can lead to a lower risk of developing breast cancer. Surgical approaches, including bilateral risk-reduction mastectomy and salpingo-oophorectomy, are usually limited to women with a hereditary predisposition to development of breast cancer. The objective of this review is to summarize the various approaches directed at reducing the incidence of breast cancer.

Update on Prognostic Markers for Endometrial Cancer

Endometrial cancer is the most common gynecologic cancer in the USA and the second most common worldwide after cervical cancer. While common symptomatology of endometrial cancer leads to early diagnosis and favorable 5-year survival in most cases, there is a subset of cancers that have a poorer prognosis. The clinical and pathologic prognostic factors for endometrial cancer are well known and instrumental in determining the need for adjuvant therapy. Recently, research has been focused on the identification of molecular changes leading to different histologic subtypes to improve classification of endometrial cancer. The identification of novel mutations and molecular profiles should enhance our ability to personalize adjuvant treatment with genome-guided targeted therapy.

Metformin may reduce bladder cancer risk in Taiwanese patients with type 2 diabetes

Whether metformin therapy affects bladder cancer risk in patients with type 2 diabetes mellitus (T2DM) has not been extensively investigated. The reimbursement databases of all Taiwanese patients with a new diagnosis of T2DM between 1998 and 2002 (n = 940,708) were retrieved from the National Health Insurance for follow-up of bladder cancer up to the end of 2009. Metformin was treated as a time-dependent variable, and of these patients, 532,519 were never-users and 408,189 were ever-users of metformin. A time-dependent approach was applied in the calculation of bladder cancer incidence and in the estimation of hazard ratios by Cox regression for ever-users, never-users, and subgroups of metformin exposure (using tertile cutoffs of cumulative duration of therapy and cumulative dose). During the study period, 1,847 (0.45%) metformin ever-users and 6,213 (1.17%) metformin never-users developed bladder cancer, representing an incidence of 72.03 and 189.22 per 100,000 person-years, respectively. The age-sex-adjusted and multivariable-adjusted hazard ratios (95% confidence intervals) for ever- versus never-users were 0.382 (0.360-0.405) and 0.600 (0.564-0.638), respectively. The multivariable-adjusted hazard ratios for the first, second, and third tertiles of cumulative duration of metformin therapy were 1.034 (0.954-1.120), 0.696 (0.632-0.766), and 0.258 (0.229-0.291), respectively (P trend <0.0001). Similarly, the multivariable-adjusted hazard ratios for the first, second, and third tertiles of cumulative dose of metformin were 0.997 (0.920-1.080), 0.615 (0.559-0.677), and 0.285 (0.253-0.321), respectively (P trend <0.0001). This study suggests that metformin use is associated with a decreased risk of bladder cancer in patients with T2DM.

Obesity and cancer pathogenesis

Overweight and obesity have reached pandemic levels on a worldwide basis and are associated with increased risk and worse prognosis for many but not all malignancies. Pathophysiologic processes that affect this association are reviewed, with a focus on the relationship between type 2 diabetes mellitus and cancer, lessons learned from the use of murine models to study the association, the impact of obesity on pancreatic cancer, the effects of dietary fats and cholesterol on cancer promotion, and the mechanisms by which the intestinal microbiome affects obesity and cancer.

Advances in Preventive Therapy for Estrogen-Receptor-Negative Breast Cancer

Preventing breast cancer is an effective strategy for reducing breast cancer deaths. The purpose of chemoprevention (also termed preventive therapy) is to reduce cancer incidence by use of natural, synthetic, or biological agents. The efficacy of tamoxifen, raloxifene, and exemestane as preventive therapy against estrogen-receptor (ER)-positive breast cancer is well established for women at increased risk for breast cancer. However, because breast cancer is a heterogeneous disease, distinct preventive approaches may be required for effective prevention of each subtype. Current research is, therefore, focused on identifying alternative mechanisms by which biologically active compounds can reduce the risk of all breast cancer subtypes including ER-negative breast cancer. Promising agents are currently being developed for prevention of HER2-positive and triple-negative breast cancer (TNBC) and include inhibitors of the ErbB family receptors, COX-2 inhibitors, metformin, retinoids, statins, poly(ADP-ribose) polymerase inhibitors, and natural compounds. This review focuses on recent progress in research to develop more effective preventive agents, in particular for prevention of ER-negative breast cancer.

Breast cancer prevention by antihormones and other drugs: where do we stand?

Breast cancer is the most common cancer in women worldwide. The selective estrogen-receptor (ER) modulators tamoxifen and raloxifene are approved by the Food and Drug Administration for the preventive therapy of breast cancer. Other drugs have shown promise but need further assessment. In the present review, we present an update of the chemoprevention of ER-positive breast cancer and discuss the potential role of metformin and aspirin, 2 drugs other than the specific "antihormones."

Hype versus hope: metformin and vitamin D as anticancer agents

There has been increasing interest in the use of metformin and vitamin D to reduce cancer risk and improve outcomes. Metformin, an oral antidiabetic drug, improves insulin resistance and has been associated with reduced cancer incidence and cancer mortality. Low levels of vitamin D have also been associated with increased cancer risk, mainly in retrospective studies, and it has been suggested that vitamin D supplementation might play a role in cancer prevention. Preclinical data provide a biologic rationale for these associations; however, the human data arise predominantly from observational studies and caution is needed in their translation into clinical practice. This is because of the recognized limitations of observational studies, such as time-related survival biases, selection and referral biases, short follow-up, and the presence of confounding factors that can lead to spurious or inaccurate findings. Combined examination of associations with cancer risk and outcome (occurring when exposure in a population that does not yet have cancer is analyzed in relation to cancer death) may yield results that are difficult to interpret. Finally, associations across all cancers may differ from those in specific cancer types. These shortcomings can be overcome in properly designed and adequately powered prospective randomized trials; however, such trials are both expensive and time consuming. We review the literature examining the associations of metformin and vitamin D with cancer, discussing weakness and strengths and making recommendations for further research and clinical practice.

Metformin use and endometrial cancer survival

OBJECTIVE

Impaired glucose tolerance and diabetes are risk factors for the development of uterine cancer. Although greater progression free survival among diabetic patients with ovarian and breast cancers using metformin has been reported, no studies have assessed the association of metformin use with survival in women with endometrial cancer (EC).

METHODS

We conducted a single-institution retrospective cohort study of all patients treated for uterine cancer from January 1999 through December 2009. Demographic, medical, social, and survival data were abstracted from medical records and the national death registry. Overall survival (OS) was estimated using Kaplan-Meier methods. Cox models were utilized for multivariate analysis. All statistical tests were two-sided.

RESULTS

Of 985 patients, 114 (12%) had diabetes and were treated with metformin, 136 (14%) were diabetic but did not use metformin, and 735 (74%) had not been diagnosed with diabetes. Greater OS was observed in diabetics with non-endometrioid EC who used metformin than in diabetic cases not using metformin and non-endometrioid EC cases without diabetes (log rank test (p=0.02)). This association remained significant (hazard ratio=0.54, 95% CI: 0.30-0.97, p<0.04) after adjusting for age, clinical stage, grade, chemotherapy treatment, radiation treatment and the presence of hyperlipidemia in multivariate analysis. No association between metformin use and OS in diabetics with endometrioid histology was observed.

CONCLUSION

Diabetic EC patients with non-endometrioid tumors who used metformin had lower risk of death than women with EC who did not use metformin. These data suggest that metformin might be useful as adjuvant therapy for non-endometrioid EC.

Evaluation of Diabetic Patients with Breast Cancer Treated with Metformin during Adjuvant Radiotherapy

Purpose. The purpose of this study was to evaluate acute locoregional toxicity in patients with breast cancer receiving concurrent metformin plus radiation therapy. Methods and Materials. Diabetic breast cancer patients receiving concurrent metformin and radiation therapy were matched with nondiabetic patients and diabetic patients using an alternative diabetes medication. Primary endpoints included the presence of a treatment break and development of dry or moist desquamation. Results. There was a statistically significant increase in treatment breaks for diabetic patients receiving concurrent metformin when compared to the nondiabetic patients (P value = 0.02) and a trend toward significance when compared to diabetic patients receiving an alternate diabetes medication (P value = 0.08). Multiple logistic regression analysis demonstrated concurrent metformin use as being associated with a trend toward the predictive value of determining the incidence of developing desquamation in diabetic patients receiving radiation therapy compared to diabetic patients receiving an alternate diabetes medication (P value = 0.06). Conclusions. Diabetic patients treated with concurrent metformin and radiation therapy developed increased acute locoregional toxicity in comparison with diabetic patients receiving an alternate diabetes medication and nondiabetic patients. Further clinical investigation should be conducted to determine the therapeutic ratio of metformin in combination with radiation therapy.

Diabetes and cancer relationships

Diabetes and cancer are both heterogeneous and multifactorial diseases with tremendous impact on health worldwide. Epidemiologic evidence suggests that certain malignancies may be associated with diabetes, as well as with diabetes risk factors and, perhaps, with certain diabetes treatments. Numerous biological mechanisms could account for these relationships. Insulin-like growth factor (IGF)-1, IGF-2, IGF-1 receptors, insulin, and the insulin receptor play roles in the development and progression of cancers. Although evidence from randomized controlled trials does not support or refute associations of diabetes and its treatments with either increased or reduced risk of cancer incidence or prognosis, consideration of malignancy incidence rates and the magnitude of the trials that would be required to address these issues explains why such studies may not be readily undertaken.

Metformin: On Ongoing Journey across Diabetes, Cancer Therapy and Prevention

Cancer metabolism is the focus of intense research, which witnesses its key role in human tumors. Diabetic patients treated with metformin exhibit a reduced incidence of cancer and cancer-related mortality. This highlights the possibility that the tackling of metabolic alterations might also hold promising value for treating cancer patients. Here, we review the emerging role of metformin as a paradigmatic example of an old drug used worldwide to treat patients with type II diabetes which to date is gaining strong in vitro and in vivo anticancer activities to be included in clinical trials. Metformin is also becoming the focus of intense basic and clinical research on chemoprevention, thus suggesting that metabolic alteration is an early lesion along cancer transformation. Metabolic reprogramming might be a very efficient prevention strategy with a profound impact on public health worldwide.

The impact of comorbidity on cancer survival: a review

Background

A number of studies have shown poorer survival among cancer patients with comorbidity. Several mechanisms may underlie this finding. In this review we summarize the current literature on the association between patient comorbidity and cancer prognosis. Prognostic factors examined include tumor biology, diagnosis, treatment, clinical quality, and adherence.

Methods

All English-language articles published during 2002–2012 on the association between comorbidity and survival among patients with colon cancer, breast cancer, and lung cancer were identified from PubMed, MEDLINE and Embase. Titles and abstracts were reviewed to identify eligible studies and their main results were then extracted.

Results

Our search yielded more than 2,500 articles related to comorbidity and cancer, but few investigated the prognostic impact of comorbidity as a primary aim. Most studies found that cancer patients with comorbidity had poorer survival than those without comorbidity, with 5-year mortality hazard ratios ranging from 1.1 to 5.8. Few studies examined the influence of specific chronic conditions. In general, comorbidity does not appear to be associated with more aggressive types of cancer or other differences in tumor biology. Presence of specific severe comorbidities or psychiatric disorders were found to be associated with delayed cancer diagnosis in some studies, while chronic diseases requiring regular medical visits were associated with earlier cancer detection in others. Another finding was that patients with comorbidity do not receive standard cancer treatments such as surgery, chemotherapy, and radiation therapy as often as patients without comorbidity, and their chance of completing a course of cancer treatment is lower. Postoperative complications and mortality are higher in patients with comorbidity. It is unclear from the literature whether the apparent undertreatment reflects appropriate consideration of greater toxicity risk, poorer clinical quality, patient preferences, or poor adherence among patients with comorbidity.

Conclusion

Despite increasing recognition of the importance of comorbid illnesses among cancer patients, major challenges remain. Both treatment effectiveness and compliance appear compromised among cancer patients with comorbidity. Data on clinical quality is limited.

Association between metformin therapy and mortality after breast cancer: a population-based study

OBJECTIVE

Metformin has been associated with a reduction in breast cancer risk and may improve survival after cancer through direct and indirect tumor-suppressing mechanisms. The purpose of this study was to evaluate the effect of metformin therapy on survival in women with breast cancer using methods that accounted for the duration of treatment with glucose-lowering therapies.

RESEARCH DESIGN AND METHODS

This population-based study, using Ontario health care databases, recruited women aged 66 years or older diagnosed with diabetes and breast cancer between 1 April 1997 and 31 March 2008. Using Cox regression analyses, we explored the association between cumulative duration of past metformin use and all-cause and breast cancer-specific mortality. We modeled cumulative duration of past metformin use as a time-varying exposure.

RESULTS

Of 2,361 breast cancer patients identified, mean (±SD) age at cancer diagnosis was 77.4±6.3 years, and mean follow-up was 4.5±3.0 years. There were 1,101 deaths (46.6%), among which 386 (16.3%) were breast cancer-specific deaths. No significant association was found between cumulative duration of past metformin use and all-cause mortality (adjusted hazard ratio 0.97 [95% CI 0.92-1.02]) or breast cancer-specific mortality (0.91 [0.81-1.03]) per additional year of cumulative use.

CONCLUSIONS

Our findings failed to show an association between improved survival and increased cumulative metformin duration in older breast cancer patients who had recent-onset diabetes. Further research is needed to clarify this association, accounting for effects of cancer stage and BMI in younger populations or those with differing stages of diabetes as well as in nondiabetic populations.

Beyond aspirin-cancer prevention with statins, metformin and bisphosphonates

Cancer risk reduction using pharmacological means is an attractive modern preventive approach that supplements the classical behavioural prevention recommendations. Medications that are commonly used by large populations to treat a variety of common, non-cancer-related, medical situations are an attractive candidate pool. This Review discusses three pharmacological agents with the most evidence for their potential as cancer chemopreventive agents: anti-hypercholesterolaemia medications (statins), an antidiabetic agent (metformin) and antiosteoporosis drugs (bisphosphonates). Data are accumulating to support a significant negative association of certain statins with cancer occurrence or survival in several major tumour sites (mostly gastrointestinal tumours and breast cancer), with an augmented combined effect with aspirin or other non-steroidal anti-inflammatory drugs. Metformin, but not other hypoglycaemic drugs, also seems to have some antitumour growth activity, but the amount of evidence in human studies, mainly in breast cancer, is still limited. Experimental and observational data have identified bisphosphonates as a pharmacological group that could have significant impact on incidence and mortality of more than one subsite of malignancy. At the current level of evidence these potential chemopreventive drugs should be considered in high-risk situations or using the personalized approach of maximizing individual benefits and minimizing the potential for adverse effects with the aid of pharmacogenetic indicators.

Effects of sulfonylureas on tumor growth: a review of the literature

Type 2 diabetes mellitus patients are at higher cancer risk, probably because of hyperinsulinemia and insulin growth factor 1 pathway activation. The effects of antidiabetic drugs on cancer risk have been described and discussed in several studies suggesting opposite effects of the biguanide metformin and sulfonylureas on cancer incidence and mortality. The anticancer mechanisms of metformin have been clarified, and some clinical studies, particularly in breast cancer patients, have been published or are currently ongoing; however, data about the effects of sulfonylureas on cancer growth are less consistent. The aims of this work are to review preclinical evidence of second-generation sulfonylureas effects on tumor growth, to clarify the potential mechanisms of action, and to identify possible metabolic targets for patient selection. Most evidence is on the adenosine triphosphate-sensitive potassium channels inhibitor glibenclamide, which interacts with reactive oxygen species production thus inducing cancer cell death. Among diarylsulfonylureas, next-generation DW2282 derivatives are particularly promising because of the proapoptotic activity in multidrug-resistant cells.

Metformin therapy and risk of cancer in patients with type 2 diabetes: systematic review

Aims/Hypothesis

Diabetes treatments were related with either an increased or reduced risk of cancer. There is ongoing debate about a potential protective action of metformin. To summarize evidence on the association between metformin and risk of cancer and cancer mortality in patients with diabetes.

Methods

Data source: MEDLINE and EMBASE (January 1966-April 2012). We selected randomized studies comparing metformin and other hypoglycaemic agents and observational studies exploring the association between exposure to metformin and cancer. Outcomes were cancer mortality, all malignancies and site-specific cancers.

Results

Of 25307 citations identified, 12 randomized controlled trials (21,595 patients) and 41 observational studies (1,029,389 patients) met the inclusion criteria. In observational studies there was a significant association of exposure to metformin with the risk of cancer death [6 studies, 24,410 patients, OR:0.65, 95%CI: 0.53-0.80], all malignancies [18 studies, 561,836 patients, OR:0.73, 95%CI: 0.61-0.88], liver [8 studies, 312,742 patients, OR:0.34; 95%CI: 0.19-0.60] colorectal [12 studies, 871,365 patients, OR:0.83, 95%CI: 0.74–0.92], pancreas [9 studies, 847,248 patients, OR:0.56, 95%CI: 0.36–0.86], stomach [2 studies, 100701 patients, OR:0.83, 95%CI: 0.76–0.91], and esophagus cancer [2 studies, 100694 patients, OR:0.90, 95%CI: 0.83–0.98]. No significant difference of risk was observed in randomized trials. Metformin was not associated with the risk of: breast cancer, lung cancer, ovarian cancer, uterus cancer, prostate cancer, bladder cancer, kidney cancer, and melanoma.

Conclusions/Interpretation

Results suggest that Metformin might be associated with a significant reduction in the risk of cancer and cancer-related mortality. Randomized trials specifically designed to evaluate the efficacy of metformin as an anticancer agent are warranted.

The impact of diabetes mellitus on breast cancer outcomes: a single center retrospective study

Diabetes mellitus has been implicated to affect the prognostic outcomes of patients with various types of cancer. This study explores the impact of diabetes mellitus on the survival outcomes of patients with all stages of breast cancer. We performed a retrospective analysis of 255 patients with all stages of breast cancer. Survival outcomes were compared for diabetic and non-diabetic patients. A greater percent of patients in the non-diabetic group (54.1%) presented with early-stage (stage 0 and 1) cancer than diabetics for which 41.2% presented with stage 0 or 1 breast cancer; however this difference did not achieve statistical significance (p = 0.068). Overall, we observed a significant difference in survival between the diabetics and non-diabetic subjects (p = 0.001). Even after adjustment for all covariates and after stratification for Body Mass Index (BMI), diabetics were found to have a poorer prognosis in terms of survival time. In patients with breast cancer, diabetes mellitus is an independent predictor of lower overall survival rates, even after adjusting for other comorbidities. Primary caregivers and oncologists alike should aggressively screen breast cancer patients for diabetes mellitus and vice versa.

Black race as a prognostic factor in triple-negative breast cancer patients treated with breast-conserving therapy: a large, single-institution retrospective analysis

Triple-negative breast cancer (TNBC) disproportionately affects black women. However, black race as a prognostic factor in TNBC has not been well studied. We evaluated the effect of race, among other variables, on outcomes in women with TNBC. A total of 704 patients with stages I-III TNBC treated with breast-conserving surgery ± adjuvant radiation therapy (RT) and chemotherapy were identified from an institutional database. Competing risk analyses, Kaplan-Meier methods, and Cox proportional hazards models identified associations among clinicopathologic variables on locoregional recurrence (LRR), distant recurrence (DR), and overall survival (OS). LRR was defined as a biopsy proven, triple receptor-negative recurrence in the ipsilateral breast or regional lymph nodes. At a median follow-up of 51 months, there were 55 LRR, 61 DR, and 111 death events. Compared to non-black women, black women had higher disease stage and were more likely to receive axillary lymph node dissection, chemotherapy, and nodal irradiation (all P < 0.05). After adjustment for stage, age, lymphovascular invasion, chemotherapy, and RT on multivariate analysis, black race was prognostic for increased risk of LRR (hazard ratio [HR] = 3.17; 95 % confidence interval: 1.7-5.8; P = 0.0002). The 5-year risk of regional recurrence was higher in black women (10 vs. 2 %, P < 0.0001), but local failures were similar between groups (3.0 vs. 5.3 %, P = 0.15). RT was an independent predictor for decreased LRR and increased OS on multivariate analyses (P = 0.0006 and P = 0.0003, respectively). Black women with TNBC had equivalent local control, but higher risk of regional nodal failure, compared with non-black counterparts. The routine use of comprehensive nodal irradiation may be beneficial for black women with TNBC.

Demographic and clinico-pathological characteristics in patients with invasive breast cancer receiving metformin

There was a contradictory data with metformin use on breast cancer risk, but there is growing evidence that the use of metformin in diabetic patients was associated with lower risks of breast cancer mortality and incidence. The effect of metformin on clinical and pathological properties of breast cancer was not known exactly, and we aimed to investigate the demographic and clinico-pathological characteristics of patients with metformin users at the time of breast cancer diagnosis. Patients with breast cancer diagnosed from 2000 to 2012 in our clinic were retrospectively analyzed. Patient's demographics, including survival data and tumor characteristics were obtained from medical charts. Breast cancer patients who were taking metformin at the time of breast cancer diagnosis were enrolled as metformin users (n = 148), where the patients matched with the same age who were not taking metformin were included as a control group (n = 636). A total of 784 patients were included in this study. Median age of both metformin users and nonusers was 57 (23-87). There were no significant differences in baseline tumor size (P = 0.60), tumor stage (P = 0.76), and node positivity (P = 0.13) between the two groups. Metformin user patients compared to nonusers had significantly lower incidence of histological grade III tumor (P = 0.03). A similar significant trend for lower incidence of triple negative (P = 0.01) and higher incidence ER positivity (P = 0.008) and PR positivity (P = 0.01) was also seen in metformin users. In survival analysis, the estimated median disease-free survival was 118 months in metformin users, whereas 69 months in nonusers (P = 0.09). Median overall survival (OS) could not be obtained due to low events. In patients with metformin users, OS rate was 98.4, 97.1, and 93.8 %, and in nonusers was 99.6, 94.4, and 90.5 %, the first, third, and fifth years, respectively. The use of metformin at the time of breast cancer diagnosis was associated with better clinico-pathological properties and nonsignificantly improved disease-free survival in breast cancer patients.

Postmenopausal breast cancer, androgens, and aromatase inhibitors

Recent data can help to better define the long debated relationship between androgens and breast cancer (BC) after menopause. We reviewed the available literature data on: the origin of androgens after menopause, the association between circulating androgens and BC incidence and recurrence, the relationship between circulating and intratumoral hormones, the prognostic significance of the presence of androgen receptors (ARs) in the different BC subtypes, the androgen effect on BC cell lines, and the relationship between androgens and aromatase inhibitors. Epidemiological, clinical, and preclinical data on the role of androgens and of ARs on estrogen receptor (ER)-negative BC are somewhat controversial. However, most preclinical studies suggest that activated ARs, when present, have a proliferative effect, particularly in HER2 expressing cell lines, due to the cross-talk between AR and HER2 pathways. As regards ER-positive BC, epidemiological studies associate androgen levels with increased incidence and risk of recurrences, whilst clinical studies associate the AR positivity with a better prognosis. Preclinical studies suggest that the action of androgens is bidirectional: mainly proliferative, because circulating androgens are the precursors of estrogens, but also anti-proliferative, because AR activation restrains ER activity. The relative increase of androgenic action that follows the blocking of androgen aromatization into estrogens by aromatase inhibitors (AIs), could contribute to their therapeutic efficacy in AR-positive cases. Available data, although defining a complex picture, suggest that circulating androgen levels are clinically relevant, particularly when AIs are used.

Obesity, diabetes mellitus, and the risk of female breast cancer in Eastern China

Background

This study was designed to explore the relationship between obesity, diabetes mellitus (DM), and female breast cancer in Eastern China.

Methods

A 1:3 matched case–control study was carried out, comprising 123 women with breast cancer and 369 controls. All of the 492 subjects were selected from a previous epidemiological survey of 122,058 women in Eastern China.

Results

There were significant differences between the case and control groups in waist circumference and body mass index (BMI), but not in waist to hip ratio or hip circumference. There was a significant difference between the two groups in BMI for post-menopausal women, and a significant difference in waist circumference for pre-menopausal women. After adjustment for other factors, BMI was still significantly associated with breast cancer (odds ratio (OR) = 1.58, 95% confidence interval (CI) 1.14 to 2.19). DM was significantly associated with breast cancer (OR = 3.35, 95% CI 1.02 to 11.01) in the univariate analysis but not in the multivariate analysis (P = 0.059).

Conclusions

Obesity might be a risk factor for female breast cancer. We found different strengths of association for women with different menopausal status when we examined the relationship between obesity and breast cancer. The association between DM and female breast cancer should be further confirmed with larger sample sizes.

Metformin and cancer

Type 2 diabetes mellitus is a rising cause of cardiovascular morbidity and mortality. A number of studies have also identified diabetic patients as having increased risk for the development of cancer. Metformin is a widely prescribed antidiabetic drug with an established efficacy coupled with a favorable safety profile and low cost. An increasing number of studies have associated metformin treatment with a decrease of cancer risk. Moreover, metformin has also been associated with improved outcomes in cancer patients. These possible pleiotropic effects of metformin may establish metformin as a cancer prevention and treatment option. However, any favorable effects of metformin on cancer are not always corroborated by clinical trials. Larger studies are expected to better investigate the possible antineoplastic effects of metformin.

Association of metformin use with cancer incidence and mortality: a meta-analysis

PURPOSE

To assess the effect of metformin intake on cancer incidence and mortality.

METHODS

Original articles in English published until June 15, 2012 were searched for in electronic databases (MEDLINE, ISI Web of Science and EMBASE databases) and relevant reviews were examined. Meta-analysis was applied to calculate the summary relative risk (SRR) and their 95% confidence intervals (95% CI). Sensitivity analysis was conducted to assess the robustness of the pooled estimator. The risk of publication bias was assessed by the Egger regression asymmetry test.

RESULTS

According to the eligibility criteria, 37 studies comprising 1,535,636 participants, were selected in terms of intervention and data of cancer incidence or mortality. Among metformin users compared with non-users, the SRR for overall-cancer incidence was 0.73 (95% CI, 0.64-0.83) and that for mortality was 0.82 (95% CI, 0.76-0.89). The risk reductions for liver, pancreatic, colorectal and breast cancer incidence were 78%, 46%, 23% and 6%, respectively. Also, metformin can reduce the mortality of liver cancer (SRR, 0.23; 95% CI, 0.09-0.60) and breast cancer (SRR, 0.63; 95% CI, 0.40-0.99). No statistically significant association between metformin and prostate cancer incidence was found.

CONCLUSIONS

Metformin can reduce the incidence of overall cancer, liver cancer, pancreatic cancer, colorectal cancer and breast cancer as well as the mortality of overall cancer, liver cancer and breast cancer. No beneficial effect on prostate cancer incidence was found for meformin intake in the meta-analysis.

Type 2 diabetes mellitus, oral diabetic medications, insulin therapy, and overall breast cancer risk

Breast cancer is among the most common cancers worldwide. Diabetes is an important chronic health problem associated with insulin resistance, increased insulin level, changes in growth hormones and factors, and activation of mitogen-activating protein kinase (MAPK) pathways, leading to an increased breast cancer risk. This paper looked at the epidemiologic studies of the association between type 2 diabetes and risk of breast cancer and its effect on overall cancer-specific survival. The combined evidence overall supported a modest association between type 2 diabetes and the risk of breast cancer, which was found to be more prevalent among postmenopausal women. Effect of oral diabetics and insulin therapy on breast cancer risk was also evaluated. It was found that metformin and thiazolidinones tended to have a protective role. Metformin therapy trials for its use as an adjuvant for breast cancer treatment are still ongoing. Sulfonylurea and insulin therapy were found to be mildly associated with increased overall cancers. No evidence or studies evaluated the association of DPPIV inhibitors and GLP 1 agonists with breast cancer risk because of their recent introduction into the management of diabetes.

Clinical pathological characteristics and prognostic analysis of 1,013 breast cancer patients with diabetes

The purpose of this study was to investigate the clinical, pathological, and prognostic characteristics of breast cancer patients with diabetes. In total, the study included 1,013 breast cancer patients with diabetes and 4,621 breast cancer patients without diabetes. Patients with diabetes were further divided into the metformin- and nonmetformin-treated subgroups. The percentage of elderly patients (P < 0.001), obese patients (P < 0.001), and menopausal patients (P < 0.001) as well as the percentage of patients with cardio-cerebrovascular complications (P < 0.001), negative PR (P < 0.001) expression, or low Ki67 expression (P = 0.001) tended to be higher in the diabetic group. In addition, these patients had later pathological stages (P < 0.001), more lymph node metastasis (P = 0.014), and a lower percentage of them were on the anthracycline-based chemotherapy regimen (P = 0.003). The diabetic group was further divided into the metformin and nonmetformin-treated subgroups. The pairwise comparison between the metformin-treated subgroup and the control group did not show a significant difference in the pathological stages (P = 0.0079). However, the HER-2 positive rate tended to be lower in the metformin-treated subgroup than in the nonmetformin-treated subgroup (P = 0.002). No significant difference was found in the lymph node status between the nonmetformin-treated subgroup and the control group (P = 0.057), while the nonmetformin-treated subgroup was associated with higher HER-2 positive expression (P = 0.002). The median follow-up time for this study was 68 months (10-120 months). In Kaplan-Meier analysis, The diabetic group predicted worse survival compared with the control group (P < 0.001) with 5-year survival rates of 79 and 82 %, respectively. The breast cancer mortality rates in the metformin-treated subgroup, the nonmetformin-treated subgroup, and the control group were significantly different (long-rank test, P < 0.001), and the 5-year survival rates were 88, 73, and 82 %, respectively. As shown in the multivariate survival analysis using Cox's regression model, compared with the control group, the metformin-treated subgroup was associated with lower mortality risk (HR 0.762; 95 % CI 0.6-0.968; P = 0.026), whereas the nonmetformin-treated subgroup was associated with higher mortality risk (HR 1.708; 95 % CI 1.461-1.997; P < 0.001). In conclusion, the diabetic group is associated with poor prognosis. Compared with the control group, the metformin-treated subgroup is associated with better clinical outcomes, while nonmetformin-treated subgroup with poorer prognosis. The selection of different antidiabetic drugs may impact the prognosis of breast cancer patients with diabetes.

The epidemiology and molecular mechanisms linking obesity, diabetes, and cancer

The worldwide epidemic of obesity is associated with increasing rates of the metabolic syndrome and type 2 diabetes. Epidemiological studies have reported that these conditions are linked to increased rates of cancer incidence and mortality. Obesity, particularly abdominal obesity, is associated with insulin resistance and the development of dyslipidemia, hyperglycemia, and ultimately type 2 diabetes. Although many metabolic abnormalities occur with obesity and type 2 diabetes, insulin resistance and hyperinsulinemia appear to be central to these conditions and may contribute to dyslipidemia and altered levels of circulating estrogens and androgens. In this review, we will discuss the epidemiological and molecular links between obesity, type 2 diabetes, and cancer, and how hyperinsulinemia and dyslipidemia may contribute to cancer development. We will discuss how these metabolic abnormalities may interact with estrogen signaling in breast cancer growth. Finally, we will discuss the effects of type 2 diabetes medications on cancer risk.

Metformin and cancer: from the old medicine cabinet to pharmacological pitfalls and prospects

Metformin is a biguanide derivative used in the treatment of type II diabetes (T2D) and one of the world's most widely prescribed drugs. Owing to its safety profile, it has been recently promoted for a range of other indications, particularly for its role in cancer prevention. There is evidence from studies in diabetic cohorts, as well as laboratory studies, that the action of metformin depends on a balance between the concentration and duration of exposure, which depends crucially on cell- and tissue-specific pharmacological factors. Mechanistic studies have revealed the involvement of increasingly complex pathways. Yet, there are several missing links regarding the role of drug transporters and drug-drug interactions, as well as the expression levels of transporters in normal versus tumor tissues, which may affect patient exposure and dosing when metformin is used in cancer prevention. This review highlights the current knowledge on metformin action and pharmacology, including novel insights into genomic factors, with a specific focus on cancer prevention. Furthermore, future challenges that may influence therapeutic outcome will be discussed.

Diabetes increases the risk of breast cancer: a meta-analysis

The aim of this meta-analysis was to collate and analyse all primary observational studies investigating the risk of breast cancer (BC) associated with diabetes. In addition, we aimed to complete subgroup analyses by both type of diabetes and gender of study participants to further clarify the origin of any such association between the two. Studies were obtained from a database search of MEDLINE, EMBASE, PubMed, Current Contents Connect and Google Scholar with additional cross-checking of reference lists. Collated data were assessed for heterogeneity and a pooled odds ratio (OR) calculated. Forty-three studies were included in the meta-analysis with 40 studies investigating BC in women and six studies investigating BC in men. Overall, we found a significantly increased risk of BC associated with diabetes in women (OR 1.20, 95% confidence interval (CI) 1.13-1.29). After subgroup analysis by type of diabetes, the association was unchanged with type 2 diabetes (OR 1.22, 95% CI 1.07-1.40) and nullified with gestational diabetes (OR 1.06, 95% CI 0.79-1.40). There were insufficient studies to calculate a pooled OR of the risk of BC associated with type 1 diabetes. There was an increased risk of BC in males with diabetes mellitus; however, the results did not reach statistical significance (OR 1.29, 95% CI 0.99-1.67). In conclusion, diabetes increases the risk of BC in women. This association is confirmed in women with type 2 diabetes and supports the hypothesis that diabetes is an independent risk factor for BC.

Carbon source and myc expression influence the antiproliferative actions of metformin

Epidemiologic and experimental data have led to increased interest in possible roles of biguanides in cancer prevention and/or treatment. Prior studies suggest that the primary action of metformin is inhibition of oxidative phosphorylation, resulting in reduced mitochondrial ATP production and activation of AMPK. In vitro, this may lead to AMPK-dependent growth inhibition if AMPK and its effector pathways are intact or to an energetic crisis if these are defective. We now show that the effect of exposure of several transformed cell lines to metformin varies with carbon source: in the presence of glutamine and absence of glucose, a 75% decrease in cellular ATP and an 80% decrease in cell number is typical; in contrast, when glucose is present, metformin exposure leads to increased glycolysis, with only a modest reduction in ATP level and cell number. Overexpression of myc was associated with sensitization to the antiproliferative effects of metformin, consistent with myc involvement in "glutamine addiction". Our results reveal previously unrecognized factors that influence metformin sensitivity and suggest that metformin-induced increase in glycolysis attenuates the antiproliferative effects of the compound.

Diabetes and pancreatic cancer

Epidemiological studies clearly indicate that the risk of pancreatic cancer (PC) is increased in diabetic patients, but most studies focus on overall diabetes or type 2 diabetes mellitus (T2DM), and there are few studies on the risks of type 1 and type 3c (secondary) diabetes. Possible mechanisms for increased cancer risk in diabetes include cellular proliferative effects of hyperglycemia, hyperinsulinemia, and abnormalities in insulin/IGF receptor pathways. Recently, insulin and insulin secretagogues have been observed to increase the PC risk, while metformin treatment reduces the cancer risk in diabetic subjects. In addition, anticancer drugs used to treat PC may either cause diabetes or worsen coexisting diabetes. T3cDM has emerged as a major subset of diabetes and may have the highest risk of pancreatic carcinoma especially in patients with chronic pancreatitis. T3cDM is also a consequence of PC in at least 30% of patients. Distinguishing T3cDM from the more prevalent T2DM among new-onset diabetic patients can be aided by an assessment of clinical features and confirmed by finding a deficiency in postprandial pancreatic polypeptide release. In conclusion, diabetes and PC have a complex relationship that requires more clinical attention. The risk of developing PC can be reduced by aggressive prevention and treatment of T2DM and obesity and the prompt diagnosis of T3cDM may allow detection of a tumor at a potentially curable stage.

Weight gain, metabolic syndrome, and breast cancer recurrence: are dietary recommendations supported by the data?

Metabolic syndrome, which can include weight gain and central obesity, elevated serum insulin and glucose, and insulin resistance, has been strongly associated with breast cancer recurrence and worse outcomes after treatment. Epidemiologic and prospective data do not show conclusive evidence as to which dietary factors may be responsible for these results. Current strategies employ low-fat diets which emphasize supplementing calories with increased intake of fruit, grain, and vegetable carbohydrate sources. Although results thus far have been inconclusive, recent randomized trials employing markedly different dietary strategies in noncancer patients may hold the key to reducing multiple risk factors in metabolic syndrome simultaneously which may prove to increase the long-term outcome of breast cancer patients and decrease recurrences. Since weight gain after breast cancer treatment confers a poor prognosis and may increase recurrence rates, large-scale randomized trials are needed to evaluate appropriate dietary interventions for our breast cancer patients.

Metformin in early breast cancer: a prospective window of opportunity neoadjuvant study

Metformin may exert anti-cancer effects through indirect (insulin-mediated) or direct (insulin-independent) mechanisms. We report results of a neoadjuvant "window of opportunity" study of metformin in women with operable breast cancer. Newly diagnosed, untreated, non-diabetic breast cancer patients received metformin 500 mg tid after diagnostic core biopsy until definitive surgery. Clinical (weight, symptoms, and quality of life) and blood [fasting serum insulin, glucose, homeostasis model assessment (HOMA), C-reactive protein (CRP), and leptin] attributes were compared pre- and post-metformin as were terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and Ki67 scores (our primary endpoint) in tumor tissue. Thirty-nine patients completed the study. Mean age was 51 years, and metformin was administered for a median of 18 days (range 13-40) up to the evening prior to surgery. 51 % had T1 cancers, 38 % had positive nodes, 85 % had ER and/or PgR positive tumors, and 13 % had HER2 overexpressing or amplified tumors. Mild, self-limiting nausea, diarrhea, anorexia, and abdominal bloating were present in 50, 50, 41, and 32 % of patients, respectively, but no significant decreases were seen on the EORTC30-QLQ function scales. Body mass index (BMI) (-0.5 kg/m(2), p < 0.0001), weight (-1.2 kg, p < 0.0001), and HOMA (-0.21, p = 0.047) decreased significantly while non-significant decreases were seen in insulin (-4.7 pmol/L, p = 0.07), leptin (-1.3 ng/mL, p = 0.15) and CRP (-0.2 mg/L, p = 0.35). Ki67 staining in invasive tumor tissue decreased (from 36.5 to 33.5 %, p = 0.016) and TUNEL staining increased (from 0.56 to 1.05, p = 0.004). Short-term preoperative metformin was well tolerated and resulted in clinical and cellular changes consistent with beneficial anti-cancer effects; evaluation of the clinical relevance of these findings in adequately powered clinical trials using clinical endpoints such as survival is needed.

Investigating metformin for cancer prevention and treatment: the end of the beginning

Laboratory research and pharmacoepidemiology are providing converging evidence that the widely used antidiabetic drug metformin has antineoplastic activity, but there are caveats. Although population studies suggest that metformin exposure is associated with reduced cancer risk and/or improved prognosis, these data are mostly retrospective and nonrandomized. Laboratory models show antineoplastic activity, but metformin concentrations used in many experiments exceed those achieved with conventional doses used for diabetes treatment. Ongoing translational research should be useful in guiding design of clinical trials, not only to evaluate metformin at conventional antidiabetic doses, where reduction of elevated insulin levels may contribute to antineoplastic activity for certain subsets of patients, but also to explore more aggressive dosing of biguanides, which may lead to reprogramming of energy metabolism in a manner that could provide important opportunities for synthetic lethality through rational drug combinations or in the context of genetic lesions associated with hypersensitivity to energetic stress.

SIGNIFICANCE

There are tantalizing clues that justify the investigation of antineoplastic activities of biguanides. The complexity of their biologic effects requires further translational research to guide clinical trial design.