Metformin and the risk of endometrial cancer: A population-based cohort study

Metformin: A Dual-Role Player in Cancer Treatment and Prevention

Cancer continues to pose a significant global health challenge, as evidenced by the increasing incidence rates and high mortality rates, despite the advancements made in chemotherapy. The emergence of chemoresistance further complicates the effectiveness of treatment. However, there is growing interest in the potential of metformin, a commonly prescribed drug for type 2 diabetes mellitus (T2DM), as an adjuvant chemotherapy agent in cancer treatment. Although the precise mechanism of action of metformin in cancer therapy is not fully understood, it has been found to have pleiotropic effects, including the modulation of metabolic pathways, reduction in inflammation, and the regulation of cellular proliferation. This comprehensive review examines the anticancer properties of metformin, drawing insights from various studies conducted in vitro and in vivo, as well as from clinical trials and observational research. This review discusses the mechanisms of action involving both insulin-dependent and independent pathways, shedding light on the potential of metformin as a therapeutic agent for different types of cancer. Despite promising findings, there are challenges that need to be addressed, such as conflicting outcomes in clinical trials, considerations regarding dosing, and the development of resistance. These challenges highlight the importance of further research to fully harness the therapeutic potential of metformin in cancer treatment. The aims of this review are to provide a contemporary understanding of the role of metformin in cancer therapy and identify areas for future exploration in the pursuit of effective anticancer strategies.

Associations of metformin therapy treatment with endometrial cancer risk and prognosis: A systematic review and meta-analysis

BACKGROUND

Several abstract studies have demonstrated that metformin may be beneficial for preventing and treating endometrial cancer (EC), while the results have been inconsistent and inconclusive. This systematic review and meta-analysis aimed to investigate the association between metformin use and the incidence and mortality of endometrial cancer in diabetic patients.

METHODS

A systematic literature search was performed in Pubmed, EMBASE, Web of Science, Cochrane Library, SinoMed, CNKI, Wanfang Data, and VIP from inception to November 2022. The outcome measures were hazard ratios (HRs) comparing the EC incidence and mortality in patients with type 2 diabetes mellitus (T2DM) on metformin and non-metformin. A random or fixed-effects model was applied for data analysis, and subgroup analysis was performed to look for factors of heterogeneity. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) assessed the evidence's certainty.

RESULTS

Eleven studies reported data on EC incidence. The pooled results suggested that the use of metformin was associated with a significantly higher incidence of EC (HR = 1.17, 95% CI 1.09-1.26, P < 0.0001). Further, seventeen studies were included for survival analysis. The pooled data showed that metformin could significantly decrease all-cause mortality (HR = 0.62, 95% CI 0.52-0.74, P < 0.00001) and endometrial cancer-specific mortality (HR = 0.95, 95% CI 0.90, 1.00, P = 0.03). Finally, we noted that metformin was associated with significantly improving the progression-free survival (PFS) of EC patients with T2DM (HR = 0.55, 95% CI 0.44, 0.68, P < 0.00001).

CONCLUSIONS

This meta-analysis did not prove that metformin was beneficial for preventing EC. However, metformin could reduce their mortality risk and prolong the progression-free survival time of EC patients with T2DM.

An effective treatment approach of liposomally encapsulated metformin in colon cancer

Metformin is a drug that is widely used in the treatment of type-2 diabetes and its anticarcinogenic effect has been detected in many studies since the 2000s. Metformin has a short half-life and poor biocompatibility, which limits the activity of the drug. As a solution to this situation, our study aimed to increase the anticarcinogenic effects and reduce the side effects of metformin in colon cancer by liposomal encapsulation. For this purpose, in our study, liposome production was carried out using the thin film hydration method. The amount of metformin loaded in liposomes was determined by a standard absorbance curve at 237 nm. Size distributions and membrane zeta potentials of the liposomes were evaluated with Malvern Zetasizer ZS90. Transmission electron microscopy was performed by staining the liposomes negatively with uranyl acetate. Cultured HT-29 cells were treated with liposomal metformin or free metformin at concentrations of 0, 10, 20, and 40 mM for 24 and 48 h. At the end of the treatment period, cell viability was evaluated by CellTiter-Glo luminescent cell viability test. The anticarcinogenic effects of liposomal and free metformin on HT-29 cells were compared. As a result, liposome encapsulated metformin treatment for 24 h was more effective on HT-29 cells at 20- and 40-mM concentrations causing significantly greater decrease in the IC-50 dose compared to the free metformin. The result suggests that liposomal encapsulated metformin may offer a promising approach to increase the efficacy of the drug in the treatment of colon cancer.

Association Between Metformin Use and the Risk, Prognosis of Gynecologic Cancer

Background

For gynecological cancer patients, the beneficial effect of metformin use remains controversial due to inconsistent results of published articles. By conducting a meta-analysis, we aimed to evaluate the effect of metformin in reducing the risk and improving the survival of gynecological cancer among women with diabetes mellitus (DM).

Methods

Articles exploring association between metformin use and the risk, as well as prognosis of gynecologic cancer in DM, were searched in the databases: PubMed, Web of Science, SCOPUS, EMBASE, EBSCO, and PROQUEST. Articles were published before May 2022. All the studies were conducted using STATA 12.0 software.

Results

The meta-analysis showed no significant association between metformin use and risk of gynecologic cancer in DM with a random effects model [odds ratio (ORs)/relative risk (RR) = 0.91, 95% confidence intervals (CI) 0.77 to 1.08, I² = 84.2%, p < 0.001]. Metformin use was associated with reduced overall survival (OS) and progression-free survival (PFS) of gynecologic cancer in DM with random effects models [OS: hazard ratio (HR) = 0.60, 95% CI 0.49–0.74, I² = 55.2%, p = 0.002; PFS: HR = 0.55, 95% CI 0.33–0.91, I² = 69.1%, p = 0.006], whereas no significant association was showed between metformin use and recurrence-free survival (RFS), as well as cancer-specific survival (CSS) of gynecologic cancer in DM with random effects models (RFS: HR = 0.60, 95% CI 0.30–1.18, I² = 73.7%, p = 0.010; CSS: HR = 0.78, 95% CI 0.43–1.41, I² = 72.4%, p = 0.013).

Conclusions

In conclusion, this meta-analysis indicated that metformin may be a useful adjuvant agent for gynecological cancer with DM, especially for patients with ovarian cancer and endometrial cancer.

The Risk of Thrombosis Around Pregnancy: Where Do We Stand?

Pregnancy and puerperium increase the relative risk of venous thromboembolism (VTE) and the absolute risk remains low, around 1 per 1,000, with induced mortality of around 1 per 100,000. Analysis of large databases has helped specify the modes of presentation and risk factors (RF) whose impact is greater after than before childbirth, since VTE during pregnancy and post-partum obey different RFs. The evolution of the population concerned (mostly women over 35, obese, of multi-ethnicity undergoing medically assisted reproduction) affects the frequency of these RFs. Pulmonary embolism (PE) is over-represented after childbirth, but 30% of PE in pregnancy occurs without any RFs. Recommendations for prevention, mainly from expert groups, are heterogeneous and often discordant. Low molecular weight heparins (LMWH) are the mainstay of pharmacological thromboprophylaxis, in a field where randomized controlled studies are definitely lacking. VTE risk assessment in pregnancy must be systematic and repetitive. Risk assessment methods and scores are beginning to emerge to guide thromboprophylaxis and should be used more systematically. In the future, analyzing observational data from huge, nationwide registries and prospective cluster clinical trials may bring to light clinically relevant outcomes likely to feed comprehensive guidelines.

Metformin use and risk of cancer in patients with type 2 diabetes: a cohort study of primary care records using inverse probability weighting of marginal structural models

BACKGROUND

Previous studies provide conflicting evidence on whether metformin is protective against cancer. When studying time-varying exposure to metformin, covariates such as body mass index (BMI) and glycated haemoglobin (HbA1c) may act as both confounders and causal pathway variables, and so cannot be handled adequately by standard regression methods. Marginal structural models (MSMs) with inverse probability of treatment weights (IPTW) can correctly adjust for such confounders. Using this approach, the main objective of this study was to estimate the effect of metformin on cancer risk compared with risk in patients with T2DM taking no medication.

METHODS

Patients with incident type 2 diabetes (T2DM) were identified in the Clinical Practice Research Datalink (CPRD), a database of electronic health records derived from primary care in the UK. Patients entered the study at diabetes diagnosis or the first point after this when they had valid HbA1c and BMI measurements, and follow-up was split into 1-month intervals. Logistic regression was used to calculate IPTW; then the effect of metformin on all cancers (including and excluding non-melanoma skin cancer) and breast, prostate, lung, colorectal and pancreatic cancers was estimated in the weighted population.

RESULTS

A total of 55 629 T2DM patients were alive and cancer-free at their study entry; 2530 people had incident cancer during a median follow-up time of 2.9 years [interquartile range (IQR) 1.3-5.4 years]. Using the MSM approach, the hazard ratio (HR) for all cancers, comparing treatment with metformin with no glucose-lowering treatment, was 1.02 (0.88-1.18). Results were robust to a range of sensitivity analyses and remained consistent when estimating the treatment effect by length of exposure. We also found no evidence of a protective effect of metformin on individual cancer outcomes.

CONCLUSIONS

We find no evidence that metformin has a causal association with cancer risk.

Effect of Metformin For Decreasing Proliferative Marker in Women with Endometrial Cancer: A Randomized Double-blind Placebo-Controlled Trial

Objective:

To compare the Ki-67 index of endometrial cancer cells before and after treatment between the metformin and placebo group in women with endometrial cancer (EC).

Methods:

This study was a randomized, double-blind, placebo-controlled trial conducting in non-diabetic women who diagnosed with endometrioid EC and had a schedule for elective surgical staging at Rajavithi Hospital between August 2018 and June 2019. Tissue specimens were obtained via endometrial curettage at the time of initial diagnosis (pre-treatment) and hysterectomy (post-treatment) to assess the value of the Ki-67 index by immunochemistry. Patients were randomly assigned into 2 groups: metformin and placebo group. Metformin 850 mg or placebo 1 tab were administered once daily for at least 7 days, starting on the first morning after recruitment until one day before surgery. Baseline characteristics (e.g., age, body mass index, co-morbidities) including surgical and pathological characteristics were recorded. The metabolic effect of metformin was also evaluated by a recording of fasting blood sugar, HbA1C and potential adverse events including nausea, vomiting, dizziness, and hypoglycemic symptom.

Results:

A total of 49 EC patients were included in this study. Twenty-five patients were assigned to the metformin group and 24 patients were assigned to the placebo group. Baseline demographic, surgical, and pathological characteristics between the 2 groups were similar. Metformin significantly changed the Ki-67 index relative to placebo, with a mean decrease of 23.3% (p=0.001) and a mean proportional decrease of 39.1% (p=0.006) before and after treatment. Additionally, no significant differences were detected in metabolic effects and adverse events between the metformin and the placebo groups.

Conclusion:

Short-term treatment with an oral metformin significantly reduced a proliferative marker Ki-67 index in women with endometrioid EC awaiting surgical staging. This study supports the biological effect of metformin in EC and potential applications in the adjuvant treatment in EC patients.

Sodium-glucose co-transporter-2 inhibitor use and risk of lower-extremity amputation: Evolving questions, evolving answers

AIM

To examine whether sodium-glucose co-transporter-2 (SGLT2) inhibitors are associated with a higher risk of lower-extremity amputation than dipeptidyl-peptidase-4 (DPP-4) inhibitors and sulphonylureas.

METHODS

We conducted a retrospective cohort study, using the MarketScan Commercial Claims and Encounters Database (2013-2015), to compare the incidence of lower-extremity amputation (LEA) between initiators of SGLT2 inhibitors and initiators of two second-line drugs, DPP-4 inhibitors and sulphonylureas (SUs). We estimated crude incidence rates (IRs) and adjusted hazard ratios (aHR), with 95% confidence intervals (CIs), before and after propensity-score weighting. We additionally conducted sensitivity analyses using a comparator group of all non-metformin, non-SGLT2 inhibitor glucose-lowering drugs, as previous studies used this approach.

RESULTS

In a cohort of 328 150 individuals aged 18 to 64 years, the IR of LEA ranged from 1.5 to 2.4 per 1000 person-years. In as-treated analysis, the estimated hazard of LEA was increased among SGLT2 inhibitor initiators compared to DPP-4 inhibitor initiators (aHR 1.69, 95% CI 1.20-2.38), but not compared to SU initiators (aHR 1.02, 95% CI 0.67-1.55) or non-metformin, non-SGLT2 inhibitor initiators (aHR 1.02, 95% CI 0.54-1.93). Results were consistent in intention-to-treat analysis and across a number of sensitivity analyses.

CONCLUSIONS

Among commercially insured patients in the United States, our results suggest that initiation of SGLT2 inhibitors may increase the risk of LEA compared to initiation of DPP-4 inhibitors. Contrasting results when comparing SGLT2 inhibitor initiators to DPP-4 inhibitor and SU initiators highlight the importance of choosing appropriate comparator drugs when addressing comparative effectiveness and safety questions that can inform clinical decision-making.

The association between metformin therapy and risk of gynecological cancer in patients: Two meta-analyses

BACKGROUND

Recently, metformin, first-line drug for type 2 diabetes, has been reported to treat some gynecological tumors. However, these epidemiological studies have never been formally summarized. Considering a single study may lack the power to provide reliable conclusion, we performed two meta-analyses with different indicators to assess metformin's role in reducing the risk of gynecological cancers.

MATERIALS AND METHODS

A systematic literature search was carried out in PubMed, Medline (Ovid), Embase database (last search was performed on August 15, 2018). The relative risk (RR) along with a random-effects model were performed on Revman 5.3 and STATA 15.1 for risks analyzing.

RESULTS

A total of 1,710,080 patients in 7 studies were included in first meta-analysis. The results suggested metformin may reduce the risk of gynecological cancers (RR=0.49, 95%CI=0.29-0.82, and p=0.006). In the subgroup analyses: significantly decreased risks were found among Asians (RR=0.27, 95%CI=0.17-0.41, and p<0.00001), ovarian cancer (RR=0.18, 95%CI=0.12-0.28, and p<0.00001), and cervical cancer (RR=0.60, 95%CI=0.43-0.83, and p=0.002), but not in Caucasians (RR=0.81, 95%CI=0.50-1.32, and p=0.40) or in endometrial cancer (RR=0.71, 95%CI=0.29-1.74, and p=0.45). Meanwhile, another total of 8,335,332 cumulative follow-up years, person years, were conducted in 8 studies. The results indicated no statistical significance in general (RR=0.59, 95%CI=0.32-1.10, p=0.10), and no difference in Caucasians (RR=1.15, 95%CI=0.88-1.48, and p=0.30), endometrial cancer (RR=0.89, 95%CI=0.27-2.95, and p=0.84) or ovarian cancer (RR=0.37, 95%CI=0.09-1.49, and p=0.16) when performing subgroup analyses. However, in the subgroup analyses, results in Asians (RR=0.26, 95%CI=0.17-0.40, and p<0.00001) and cervical cancer (RR=0.56, 95%CI=0.40-0.78, and p=0.0005) had an apparent significance.

CONCLUSIONS

The results suggested the metformin can be used as a potential anticarcinogenic drug for gynecological cancers' prevention, especially for Asians and cervical cancer. The question remains, still, whether metformin is beneficial for ovarian cancer. Also, we don't know whether it is worth to give metformin to non-diabetes to prevent gynecological cancer.

Metformin as a Therapeutic Target in Endometrial Cancers

Endometrial cancer is the most common gynecologic malignancy in developed countries. Its increasing incidence is thought to be related in part to the rise of metabolic syndrome, which has been shown to be a risk factor for the development of hyperestrogenic and hyperinsulinemic states. This has consequently lead to an increase in other hormone-responsive cancers as well e.g., breast and ovarian cancer. The correlation between obesity, hyperglycemia, and endometrial cancer has highlighted the important role of metabolism in cancer establishment and persistence. Tumor-mediated reprogramming of the microenvironment and macroenvironment can range from induction of cytokines and growth factors to stimulation of surrounding stromal cells to produce energy-rich catabolites, fueling the growth, and survival of cancer cells. Such mechanisms raise the prospect of the metabolic microenvironment itself as a viable target for treatment of malignancies. Metformin is a biguanide drug that is a first-line treatment for type 2 diabetes that has beneficial effects on various markers of the metabolic syndrome. Many studies suggest that metformin shows potential as an adjuvant treatment for uterine and other cancers. Here, we review the evidence for metformin as a treatment for cancers of the endometrium. We discuss the available clinical data and the molecular mechanisms by which it may exert its effects, with a focus on how it may alter the tumor microenvironment. The pleiotropic effects of metformin on cellular energy production and usage as well as intercellular and hormone-based interactions make it a promising candidate for reprogramming of the cancer ecosystem. This, along with other treatments aimed at targeting tumor metabolic pathways, may lead to novel treatment strategies for endometrial cancer.

Metformin and cancer in type 2 diabetes: a systematic review and comprehensive bias evaluation

Background: Existing observational studies provide conflicting evidence for the causal effect of metformin use on cancer risk in patients with type-2 diabetes, and there are concerns about bias affecting a number of studies.

Methods: MEDLINE was used to identify observational studies investigating the association between metformin and overall or site-specific cancer in people with type-2 diabetes. A systematic data extraction and bias assessment was conducted, in which risk of eight bias domains (outcome, exposure, control selection, baseline confounding, time-dependent confounding, immortal time, missing data, censoring methods) were assessed against pre-defined criteria, and rated as unlikely, low, medium or high.

Results: Of 46 studies identified, 21 assessed the effect of metformin on all cancer. Reported relative risks ranged from 0.23 to 1.22, with 12/21 reporting a statistically significant protective effect and none a harmful effect. The range of estimates was similar for site-specific cancers; 3/46 studies were rated as low or unlikely risk of bias in all domains. Two of these had results consistent with no effect of metformin; one observed a moderate protective effect overall, but presented further analyses that the authors concluded were inconsistent with causality. However, 28/46 studies were at risk from bias through exposure definition, 22 through insufficient baseline adjustment and 35 from possible time-dependent confounding.

Conclusions: Observational studies on metformin and cancer varied in design, and the majority were at risk of a range of biases. The studies least likely to be affected by bias did not support a causal effect of metformin on cancer risk.

Effect of metformin use on the risk and prognosis of endometrial cancer: a systematic review and meta-analysis

BACKGROUND

Previous studies have suggested that metformin may be useful for preventing and treating endometrial cancer (EC), while the results have been inconsistent. This systematic review and meta-analysis aimed to investigate the association between metformin use and risk and prognosis of patients with EC.

METHODS

PubMed, Embase, and the Cochrane Library databases were searched for observational studies evaluating the effect of metformin on EC prevention or treatment. The odds ratio (OR) was used for analyzing risks, and the hazard ratio (HR) was used for analyzing survival outcomes. A random-effects model was used for data analysis.

RESULTS

Seven studies reported data on EC risk. The pooled results suggested that metformin was not significantly associated with a lower risk of EC [OR = 1.05, 95% confidence interval (CI) 0.82-1.35, P = 0.70]. For patients with diabetes, metformin showed no advantage in reducing the EC risk compared with other interventions (OR = 0.99, 95% CI 0.78-1.26, P = 0.95). Further, seven studies were included for survival analysis. The pooled data showed that metformin could significantly improve the overall survival of patients with EC (HR = 0.61, 95% CI 0.48-0.77, P < 0.05) and reduce the risk of EC recurrence (OR = 0.50, 95% CI 0.28-0.92, P < 0.05) Finally, we noted metformin was associated with significantly improving the overall survival of EC patients among diabetes (HR = 0.47; 95%CI 0.33-0.67, P < 0.05).

CONCLUSIONS

This meta-analysis did not prove that metformin was beneficial for preventing EC. However, metformin could prolong the overall survival of patients with EC and reduce their risk of cancer relapse.

Metformin, other antidiabetic drugs, and endometrial cancer risk: a nested case-control study within Italian healthcare utilization databases

Metformin may reduce the risk of endometrial cancer whereas other drugs for the treatment of type 2 diabetes mellitus appear to increase it, although the evidence is still limited. We investigated this issue using data from a nested case-control study within the healthcare utilization databases of the Lombardy Region, Italy. This study included 376 diabetic women with endometrial cancer and 7485 diabetic controls matched for cases on age, date at cohort entry, and duration of follow-up. We used conditional logistic regression models to estimate the odds ratio (OR) of endometrial cancer in relation to use of antidiabetic drugs, adjusted for the Charlson's comorbidity index, selected medical conditions, prescription of selected drugs, and concomitant use of other antidiabetic drugs. At cohort entry, no significant associations were observed for metformin [OR=0.99, 95% confidence interval (CI) 0.80-1.23], sulfonylureas (OR=1.14, 95% CI 0.91-1.42), insulin (OR=0.72, 95% CI 0.34-1.56), and other antidiabetic drugs (OR=1.21, 95% CI 0.75-1.95). When we considered use during follow-up, a borderline significant excess risk was found for metformin (OR=1.30, 95% CI 1.00-1.70). However, this estimate decreased to 1.07 (95% CI 0.82-1.41) when taking into account BMI using a Monte Carlo sensitivity analysis. No significant associations were found for sulfonylureas (OR=1.16, 95% CI 0.91-1.47), thiazolidinediones (OR=0.77, 95% CI 0.48-1.24), repaglinide (OR=1.32, 95% CI 0.94-1.87), incretins (OR=1.21, 95% CI 0.63-2.32), and insulin (OR=1.19, 95% CI 0.82-1.71). Our data indicate that metformin, insulin, and other antidiabetic drugs did not meaningfully affect the risk of endometrial cancer.

Metformin as an anti-cancer agent: actions and mechanisms targeting cancer stem cells

Metformin, a first line medication for type II diabetes, initially entered the spotlight as a promising anti-cancer agent due to epidemiologic reports that found reduced cancer risk and improved clinical outcomes in diabetic patients taking metformin. To uncover the anti-cancer mechanisms of metformin, preclinical studies determined that metformin impairs cellular metabolism and suppresses oncogenic signaling pathways, including receptor tyrosine kinase, PI3K/Akt, and mTOR pathways. Recently, the anti-cancer potential of metformin has gained increasing interest due to its inhibitory effects on cancer stem cells (CSCs), which are associated with tumor metastasis, drug resistance, and relapse. Studies using various cancer models, including breast, pancreatic, prostate, and colon, have demonstrated the potency of metformin in attenuating CSCs through the targeting of specific pathways involved in cell differentiation, renewal, metastasis, and metabolism. In this review, we provide a comprehensive overview of the anti-cancer actions and mechanisms of metformin, including the regulation of CSCs and related pathways. We also discuss the potential anti-cancer applications of metformin as mono- or combination therapies.

Antidiabetic medication, statins and the risk of endometrioid endometrial cancer in patients with type 2 diabetes

OBJECTIVE

To gain further evidence of an association between the incidence of endometrial cancer (EC) and the use of metformin, other antidiabetic medication (ADM) and statins in women with type 2 diabetes (T2D).

METHODS

A retrospective cohort of 92,366 women with newly diagnosed T2D was obtained from a diabetes register (FinDM). 590 endometrioid ECs were observed during the follow-up time. Poisson regression was utilized to estimate the hazard ratios (HRs) with 95% confidence intervals (95% CIs) of the endometrioid EC in relation to the use of metformin, other oral ADM, insulin and statins. Nested case-control analyses were performed, where up to 20 controls were matched for age and duration of DM for each EC case. The HRs were estimated by conditional logistic regression for never/ever and cumulative use of different forms of ADM and statins.

RESULTS

In the case-control analyses the use of metformin (HR 1.24, 95% CI 1.02-1.51) and other oral ADM (HR 1.25, 95% CI 1.04-1.50) was associated with an increased incidence of endometrioid EC compared to no ADM use. No difference was observed between metformin users and those using other oral ADMs. The use of statins was inversely related to the incidence of endometrioid EC (HR 0.78, 95% CI 0.65-0.94). Results from the full cohort analysis supported this finding.

CONCLUSIONS

In our study the use of metformin or other oral forms of ADM was not associated with a lowered risk of endometrioid EC in women with T2D. Instead statins were observed to be inversely associated with endometrioid EC in this population.

Cancer risk of sulfonylureas in patients with type 2 diabetes mellitus: A systematic review

BACKGROUND

Increasing evidence suggests that oral hypoglycemic agents used in type 2 diabetes mellitus (T2DM) may affect cancer risk. Sulfonylureas (SUs) are the most frequently used antidiabetic medications for T2DM. Whether using SUs has any effect on cancer has received considerable attention. The aim of this study was to assess the effects of SUs on cancer risk in T2DM patients.

METHODS

Published studies were identified in PubMed, EMBASE, and the Cochrane Register of Clinical Studies, and ClinicalTrials.gov was searched for additional information to identify randomized controlled trials (RCTs), cohort studies, and case-control studies. The abstracts and full text were screened, data collected, and the risk of bias assessed for each individual study.

RESULTS

Seventy-seven studies (33 RCTs, 27 cohort studies, and 17 case-control studies) were analyzed. The RCTs did not report a difference in the risk of malignant tumor between SU-treated T2DM patients and controls (odds ratio [OR] 0.96; 95% confidence interval [CI] 0.78-1.18); cohort studies showed that cancer risk was higher in patients using SUs than metformin (relative risk 1.60 [95%CI 1.37-1.87]; adjusted hazard ratio 1.13 [95%CI 1.06-1.19]), and case-control studies suggested a trend for increased cancer risk in those using SUs compared with non-SU users (adjusted OR 1.13; 95%CI 0.93-1.37).

CONCLUSIONS

The available evidence clearly shows that SUs can significantly increase the risk of cancer compared with metformin. Although the evidence suggests the possibility that SU users may have a higher risk of cancer than those using alternative medications in addition to metformin, it remains inadequate to enable definitive conclusions to be drawn.

Metformin Use Is Associated with Reduced Incidence and Improved Survival of Endometrial Cancer: A Meta-Analysis

Studies have suggested that metformin can potentially decrease the incidence of cancer and improve survival outcomes. However, the association between metformin use and the incidence and survival of endometrial cancer (EC) remains controversial. So, a meta-analysis was performed. An electronic search was conducted using PubMed, EMBASE, and Web of Science. The outcome measures were relative risks (RRs) or hazard ratios (HRs) with 95% confidence intervals (CIs) comparing the EC incidence and survival in patients treated with and without metformin. Eleven studies involving 766,926 participants were included in this study. In the pooled analysis of five studies which evaluated the association of metformin use with the incidence of EC, we found that metformin use was associated with a 13% reduction in EC risk among patients with diabetes (RR = 0.87, 95% CI: 0.80–0.95; p = 0.006). In the pooled analysis of six retrospective cohort studies evaluating the effect of metformin on the survival of EC patients, we found that, relative to nonuse, metformin use significantly improved the survival of EC patients (HR = 0.63, 95% CI: 0.45–0.87; p = 0.006). This study showed that metformin use was significantly associated with a decreased incidence of EC in diabetes and a favorable survival outcome of EC patients.

Diabetic Pharmacotherapy and Endometrial Cancer Risk Within a Publicly Funded Health Care System

OBJECTIVE

There is conflicting evidence regarding the association between metformin and endometrial cancer risk. The objective of this study was to evaluate the association between type of diabetic pharmacotherapy and endometrial cancer risk within a population-based study. The hypothesis was that metformin was associated with the lowest risk.

METHODS

This was a nested case-control study using data from the BC Cancer Registry (2000-2009) and from a province-wide prescription network (PharmaNet) since 1996. Patients were classified by drug exposure (metformin, thiazolidinediones, secretagogues, with or without insulin). The primary analysis was a conditional logistic regression to estimate the odds ratios for endometrial cancer in the drug exposure groups. Sensitivity analysis was carried out to account for uncertainty regarding various parameters. The secondary analysis evaluated the effect of dosage using a principal components analysis.

RESULTS

The study cohort comprised 492 cases and 4404 controls. The primary analysis revealed no difference in endometrial cancer risk between those using metformin and those prescribed other classes of medications (OR 1.5, 95% CI 0.9 to 2.4). Women receiving all classes of medications had almost a two-fold increase in risk (OR 1.9, 95% CI 1.1 to 3.3). The secondary analysis revealed an increased risk associated with a greater duration of treatment and number of prescriptions (OR 1.3, 95% CI 1.2 to 1.4).

CONCLUSION

In this population-based study, metformin was not associated with a decreased endometrial cancer risk. Women receiving multiple types of medications over a long time had the highest risk, implying that the extent of insulin resistance, rather than the effect of any specific medication, drives endometrial cancer risk.

Epidemiology of Endometrial Carcinoma: Etiologic Importance of Hormonal and Metabolic Influences

Endometrial carcinoma is the most common gynecologic cancer in developed nations, and the annual incidence is projected to increase, secondary to the high prevalence of obesity, a strong endometrial carcinoma risk factor. Although endometrial carcinomas are etiologically, biologically, and clinically diverse, hormonal and metabolic mechanisms are particularly strongly implicated in the pathogenesis of endometrioid carcinoma, the numerically predominant subtype. The centrality of hormonal and metabolic disturbances in the pathogenesis of endometrial carcinoma, combined with its slow development from well-characterized precursors in most cases, offers a substantial opportunity to reduce endometrial carcinoma mortality through early detection, lifestyle modification, and chemoprevention. In this chapter, we review the epidemiology of endometrial carcinoma, emphasizing theories that link risk factors for these tumors to hormonal and metabolic mechanisms. Future translational research opportunities related to prevention are discussed.

Polycystic ovary syndrome and risk of endometrial, ovarian, and breast cancer: a systematic review

Background

Polycystic ovary syndrome (PCOS) is a complex endocrine disorder with an estimated prevalence of 4–21% in reproductive aged women. The altered metabolic and hormonal environment among women with PCOS may increase their risk of some types of cancer.

Methods

We performed a comprehensive review of the literature using numerous search terms for all studies examining the associations between polycystic ovary syndrome and related characteristics and cancer published in English through October 2016. This review summarizes the epidemiological findings on the associations between PCOS and endometrial, ovarian, and breast cancers and discusses the methodological issues, complexities, and underlying mechanisms of these associations.

Results

We identified 11 individual studies and 3 meta-analyses on the associations between PCOS and endometrial cancer, 8 studies and 1 meta-analysis for ovarian cancer, and 10 studies and 1 meta-analysis for breast cancer. Multiple studies reported that women with PCOS were at a higher risk for endometrial cancer; however, many did not take into account body mass index (BMI), a strong and well-established risk factor for endometrial cancer. The association with ovarian cancer was less clear, but a potentially increased risk of the borderline serous subtype was reported by two studies. No consistent association between PCOS risk and breast cancer was observed.

Conclusion

The associations between PCOS and endometrial, ovarian, and breast cancer are complex, with the need to consider many methodological issues in future analyses. Larger well-designed studies, or pooled analyses, may help clarify these complex associations.

Metformin use and gynecological cancers: A novel treatment option emerging from drug repositioning

Metformin exerts antitumor effects mainly through AMP-activated protein kinase [AMPK] activation and phosphatidylinositol 3-kinase [PI3K]-Akt-mammalian target of rapamycin [mTOR] inhibition. This drug leads to activation of the cellular energy-sensing liver kinase B1 [LKB1]/AMPK pathway. LKB1 is implicated as a tumor suppressor gene in molecular pathogenesis of different malignancies. AMPK is a serine/threonine protein kinase that acts as an ultra-sensitive cellular energy sensor maintaining the energy balance within the cell. AMPK activation inhibits mRNA translation and proliferation in cancer cells via down-regulation of PI3K/Akt/mTOR pathway. Moreover, metformin decreases the production of insulin, insulin-like growth factor, inflammatory cytokines and vascular endothelial growth factor, and therefore it exerts anti-mitotic, anti-inflammatory and anti-angiogenetic effects. Recent in vitro and experimental data suggest that metformin electively targets cancer stem cells, and acts together with chemotherapy to block tumor growth in different cancers. Several epidemiological studies and meta-analysis have shown that metformin use is associated with decreased cancer risk and/or reduced cancer mortality for different malignancies. The present review analyzes the recent biological and clinical data suggesting a possible growth-static effect of metformin also in gynecological cancers. The large majority of available clinical data on the anti-cancer potential of metformin are based on observational studies. Therefore long-term phase II-III clinical trials are strongly warranted to further investigate metformin activity in gynecological cancers.

Lifestyle changes and the risk of developing endometrial and ovarian cancers: opportunities for prevention and management

Modifiable lifestyle factors, such as obesity, lack of physical activity, and smoking, contribute greatly to cancer and chronic disease morbidity and mortality worldwide. This review appraises recent evidence on modifiable lifestyle factors in the prevention of endometrial cancer (EC) and ovarian cancer (OC) as well as new evidence for lifestyle management of EC and OC survivors. For EC, obesity continues to be the strongest risk factor, while new evidence suggests that physical activity, oral contraceptive pills, and bariatric surgery may be protective against EC. Other medications, such as metformin and nonsteroidal anti-inflammatory drugs, may be protective, and interventional research is ongoing. For OC, we find increasing evidence to support the hypothesis that obesity and hormone replacement therapy increase the risk of developing OC. Oral contraceptive pills are protective against OC but are underutilized. Dietary factors such as the Mediterranean diet and alcohol consumption do not seem to affect the risk of either OC or EC. For EC and OC survivors, physical activity and weight loss are associated with improved quality of life. Small interventional trials show promise in increasing physical activity and weight maintenance for EC and OC survivors, although the impact on long-term health, including cancer recurrence and overall mortality, is unknown. Women's health providers should integrate counseling about these modifiable lifestyle factors into both the discussion of prevention for all women and the management of survivors of gynecologic cancers.

Metformin: A Hopeful Promise in Aging Research

Even though the inevitable process of aging by itself cannot be considered a disease, it is directly linked to life span and is the driving force behind all age-related diseases. It is an undisputable fact that age-associated diseases are among the leading causes of death in the world, primarily in industrialized countries. During the last several years, an intensive search of antiaging treatments has led to the discovery of a variety of drugs that promote health span and/or life extension. The biguanide compound metformin is widely used for treating people with type 2 diabetes and appears to show protection against cancer, inflammation, and age-related pathologies. Here, we summarize the recent developments about metformin use in translational aging research and discuss its role as a potential geroprotector.

Targeting P-glycoprotein expression and cancer cell energy metabolism: combination of metformin and 2-deoxyglucose reverses the multidrug resistance of K562/Dox cells to doxorubicin

P-glycoprotein (P-gp) is one of the major obstacles to efficiency of cancer chemotherapy. Here, we investigated whether combination of metformin and 2-deoxyglucose reverses the multidrug resistance (MDR) of K562/Dox cells and tried to elucidate the possible mechanisms. The combination of metformin and 2-deoxyglucose selectively enhanced the cytotoxicity of doxorubicin against K562/Dox cells. Metformin was not a substrate of P-gp but suppressed the elevated level of P-gp in K562/Dox cells. The downregulation of P-gp may be partly attributed to the inhibition of extracellular signal-regulated kinase pathway. The addition of 2-deoxyglucose to metformin initiated a strong metabolic stress in both K562 and K562/Dox cells. Combination of metformin and 2-deoxyglucose inhibited glucose uptake and lactate production in K562 and K562/Dox cells leading to a severe depletion in ATP and a enhanced autophagy. Above all, P-gp substrate selectively aggravated this ATP depletion effect and increased cell apoptosis in K562/Dox cells. In conclusion, metformin decreases P-gp expression in K562/Dox cells via blocking phosphorylation of extracellular signal-regulated kinase. P-gp substrate increases K562/Dox cell apoptosis via aggravating ATP depletion induced by combination of metformin and 2-deoxyglucose. Our observations highlight the importance of combination of metformin and 2-deoxyglucose in reversing multidrug resistance.

Does Metformin Reduce Cancer Risks? Methodologic Considerations

The substantial burden of cancer and diabetes and the association between the two conditions has been a motivation for researchers to look for targeted strategies that can simultaneously affect both diseases and reduce their overlapping burden. In the absence of randomized clinical trials, researchers have taken advantage of the availability and richness of administrative databases and electronic medical records to investigate the effects of drugs on cancer risk among diabetic individuals. The majority of these studies suggest that metformin could potentially reduce cancer risk. However, the validity of this purported reduction in cancer risk is limited by several methodological flaws either in the study design or in the analysis. Whether metformin use decreases cancer risk relies heavily on the availability of valid data sources with complete information on confounders, accurate assessment of drug use, appropriate study design, and robust analytical techniques. The majority of the observational studies assessing the association between metformin and cancer risk suffer from methodological shortcomings and efforts to address these issues have been incomplete. Future investigations on the association between metformin and cancer risk should clearly address the methodological issues due to confounding by indication, prevalent user bias, and time-related biases. Although the proposed strategies do not guarantee a bias-free estimate for the association between metformin and cancer, they will reduce synthesis of and reporting of erroneous results.

Expanding the therapeutic spectrum of metformin: from diabetes to cancer

INTRODUCTION

Metformin, an oral hypoglycemic agent, was introduced in the clinical practice for the treatment of type 2 diabetes mellitus more than a half-century ago. Over the years, several studies demonstrated that diabetic patients treated with metformin have a lower incidence of cancer, raising the hypothesis that the spectrum of clinical applications of the drug could be expanded also to cancer therapy. Following these initial findings, a large number of studies were performed aimed at elucidating the effects of metformin on different types of tumor, at explaining its direct and indirect anti-cancer mechanisms and at identifying the molecular pathways targeted by the drug. Several clinical trials were also performed aimed at evaluating the potential anti-cancer effect of metformin among diabetic and non-diabetic patients affected by different types of cancer. While the results of several clinical studies are encouraging, a considerable number of other investigations do not support a role of metformin as an anti-cancer agent, and highlight variables possibly accounting for discrepancies.

AIM

We hereby review the results of in vitro and in vivo studies addressing the issue of the anti-cancer effects of metformin.

CONCLUSIONS

If in vitro data appear solid, the results provided by in vivo studies are somehow controversial. In this view, larger studies are needed to fully elucidate the role of metformin on cancer development and progression, as well as the specific clinical settings in which metformin could become an anti-cancer drug.

The Impact of Diabetes on Gynecologic Cancer: Current Status and Future Directions

Diabetes mellitus has reached epidemic proportions in both the United States and worldwide with most authorities reporting a doubling in the prevalence of diabetes over the last 20-30 years. While this epidemic is closely tied to obesity, diabetes mellitus presents potential clinical challenges over and above that observed with obesity alone. From a women's health care prospective, this rise in diabetes may impact a woman's health across her lifespan. More specifically, diabetes impacts not only pregnancy as well as well as other medical conditions, but increases the risk for the development of various malignancies. From a gynecologic cancer standpoint, diabetes is most closely associated with endometrial adenocarcinomas, although increasing attention is being placed upon diabetes and ovarian cancer. Attention is also being placed on the potential role of metformin and its impact on outcomes in diabetics with cancer, as well as a potential preventative and/or adjunctive therapy for gynecologic cancer.

Metformin and endometrial cancer risk in Chinese women with type 2 diabetes mellitus in Taiwan

OBJECTIVE

To evaluate metformin effects on endometrial cancer risk in Chinese female patients with type 2 diabetes mellitus (T2DM) in Taiwan.

METHODS

This is a retrospective cohort analysis using the National Health Insurance database of Taiwan. Female patients with newly diagnosed T2DM and without endometrial cancer in 1998-2002 were followed to end of 2009 (n=478,921). Among them, 285,916 were never-users and 193,005 were ever-users of metformin. A time-dependent approach was used to calculate endometrial cancer incidence and estimate hazard ratios by Cox regression for ever-users, never-users, and subgroups of metformin exposure (tertiles of cumulative duration and cumulative dose). Sensitivity analyses were conducted in various subgroups.

RESULTS

During follow-up, 728 metformin ever-users and 2157 never-users developed endometrial cancer, representing an incidence of 60.00 and 121.69 per 100,000 person-years, respectively. The overall hazard ratio (95% confidence intervals) for ever- versus never-users after adjustment for propensity score (PS) was 0.675 (0.614-0.742). The PS-adjusted hazard ratios for the first, second, and third tertiles of cumulative duration of metformin therapy were 1.089 (0.966-1.228), 0.707 (0.616-0.812) and 0.313 (0.262-0.374), respectively (P-trend<0.0001); and 1.062 (0.942-1.197), 0.620 (0.538-0.715) and 0.376 (0.317-0.447), respectively (P-trend<0.0001), for cumulative dose of metformin. The dose-response relationship was demonstrated in various models and an overall reduced risk was consistently supported by sensitivity analyses.

CONCLUSIONS

The use of metformin in women with T2DM was associated with an overall significantly lower risk of endometrial cancer with dose-response relationship.