Metformin use and the risk of colorectal adenoma: A systematic review and meta-analysis

Metformin administration in prevention of colorectal polyps in type 2 diabetes mellitus patients

BACKGROUND

Colorectal polyps are frequently observed in patients with type 2 diabetes mellitus (DM), posing a significant risk for colorectal cancer. Metformin, a widely prescribed biguanidine drug for type 2 DM, has been suggested to have potential chemoprophylactic effects against various cancers.

AIM

To explore the correlation between colorectal polyps and metformin use in type 2 DM patients.

METHODS

Type 2 DM patients were categorized into polyp and non-polyp groups. Following this, all patients were categorized into the type 2 DM-metformin, type 2 DM-non-metformin, and non-type 2 DM groups. Based on the baseline colonoscopy results, we performed pairwise comparisons of the incidence of colorectal polyps among the three groups. Additionally, we analyzed the relationship between colorectal polyps and the duration of metformin use and between the size and number of polyps and metformin use. Simultaneously, we focused on the specific pathological types of polyps and analyzed their relationship with metformin use. Finally, we compared the incidence of polyps between metformin and non-metformin groups according to the interval colonoscopy results.

RESULTS

The rate of metformin use in patients with colorectal polyps was 0.502 times that of patients without colorectal polyps [odds ratio (OR) = 0.502, 95% confidence interval (CI): 0.365-0.689; P < 0.001]. The incidence of colorectal polyps did not differ significantly between the type 2 DM-metformin and non-type 2 DM groups (P > 0.05). Furthermore, the correlations between the duration of metformin use and the incidence of colorectal polyps and between the size and number of polyps and metformin use were not statistically significant (P > 0.05). Metformin use did not affect the incidence of colorectal polyps during interval colonoscopy (P > 0.05).

CONCLUSION

Metformin use and colorectal polyp incidence in type 2 DM patients showed a negative correlation, independent of the hypoglycemic effect of metformin.

Additive Cytotoxic and Colony-Formation Inhibitory Effects of Aspirin and Metformin on PI3KCA-Mutant Colorectal Cancer Cells

Human malignancies are one of the major health-related issues throughout the world and are anticipated to rise in the future. Despite huge investments made in anticancer drug development, limited success has been obtained and the average number of FDA approvals per year is declining. So, an increasing interest in drug repurposing exists. Metformin (MET) and aspirin (ASP) possess anticancer properties. This work aims to test the effect of these two drugs in combination on colorectal cancer (CRC) cells in vitro. The effects of MET and/or ASP on cell proliferation, viability, migratory ability, anchorage-independent growth ability (colony formation), and nutrient uptake were determined in two (HT-29 and Caco-2) human CRC cell lines. Individually, MET and ASP possessed antiproliferative, cytotoxic, and antimigratory effects and reduced colony formation in HT-29 cells (BRAF- and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit α (PI3KCA)-mutant), although MET did not affect either 3H-deoxy-D-glucose or 14C-butyrate uptake and lactate production, and ASP caused only a small decrease in 14C-butyrate uptake. Moreover, in these cells, the combination of MET and ASP resulted in a tendency to an increase in the cytotoxic effect and in a potentiation of the inhibitory effect on colony formation, although no additive antiproliferative and antimigratory effects, and no effect on nutrient uptake and lactate production were observed. In contrast, MET and ASP, both individually and in combination, were almost devoid of effects on Caco-2 cells (BRAF- and PI3KCA-wild type). We suggest that inhibition of PI3K is the common mechanism involved in the anti-CRC effect of both MET, ASP and their combination and, therefore, that the combination of MET + ASP may especially benefit PI3KCA-mutant CRC cases, which currently have a poor prognostic.

Metformin: From Diabetes to Cancer-Unveiling Molecular Mechanisms and Therapeutic Strategies

Metformin, a widely used anti-diabetic drug, has garnered attention for its potential in cancer management, particularly in breast and colorectal cancer. It is established that metformin reduces mitochondrial respiration, but its specific molecular targets within mitochondria vary. Proposed mechanisms include inhibiting mitochondrial respiratory chain Complex I and/or Complex IV, and mitochondrial glycerophosphate dehydrogenase, among others. These actions lead to cellular energy deficits, redox state changes, and several molecular changes that reduce hyperglycemia in type 2 diabetic patients. Clinical evidence supports metformin's role in cancer prevention in type 2 diabetes mellitus patients. Moreover, in these patients with breast and colorectal cancer, metformin consumption leads to an improvement in survival outcomes and prognosis. The synergistic effects of metformin with chemotherapy and immunotherapy highlights its potential as an adjunctive therapy for breast and colorectal cancer. However, nuanced findings underscore the need for further research and stratification by molecular subtype, particularly for breast cancer. This comprehensive review integrates metformin-related findings from epidemiological, clinical, and preclinical studies in breast and colorectal cancer. Here, we discuss current research addressed to define metformin's bioavailability and efficacy, exploring novel metformin-based compounds and drug delivery systems, including derivatives targeting mitochondria, combination therapies, and novel nanoformulations, showing enhanced anticancer effects.

Will metformin use lead to a decreased risk of thyroid cancer? A systematic review and meta-analyses

BACKGROUND

It has been reported that metformin use may reduce the risk of thyroid cancer, but existing studies have generated inconsistent results. The purpose of this study was to investigate such association between metformin use and the risk of thyroid cancer.

METHODS

Studies of metformin use for the risk of thyroid cancer were searched in Web of Science, PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure, China Biomedical Database, Wanfang Data, and Chinese Scientific Journals Database (VIP) from the establishment date to December 2022. Newcastle-Ottawa scale is adopted for assessing the methodological quality of included studies, and the inter-study heterogeneity was assessed by using the I-squared statistic. Combined odds ratios (ORs) with the corresponding 95% confidence intervals (CIs) were calculated through either fixed-effects or random-effects model according to the heterogeneity. Besides, subgroup analyses, sensitivity analyses and test for publication bias were conducted.

RESULTS

Five studies involving 1,713,528 participants were enrolled in the qualitative and quantitative synthesis. The result of the meta-analyses showed that metformin use was associated with a statistically significant lower risk of thyroid cancer (pooled OR = 0.68, 95% CI = 0.50-0.91, P = 0.011). Moreover, in the subgroup analysis, we found that the use of metformin may also aid in the prevention of thyroid cancer in Eastern population (pooled OR = 0.55, 95% CI = 0.35-0.88, P = 0.012) rather than Western population (pooled OR = 0.89, 95% CI = 0.52-1.54, P = 0.685). Sensitivity analysis suggested the results of this meta-analyses were relatively stable. No publication bias was detected.

CONCLUSION

Metformin use is beneficial for reducing the risk of thyroid cancer. For further investigation, more well-designed studies are still needed to elucidate the association between metformin use and the risk of thyroid cancer.

Updated Perspectives on the Diagnosis and Management of Familial Adenomatous Polyposis

Familial adenomatous polyposis (FAP) is an autosomal dominant cancer predisposition syndrome marked by extensive colorectal polyposis and a high risk of colorectal cancer (CRC). Having access to screening and enrollment programs can improve survival for patients with FAP by enabling them to undergo surgery before the development of colorectal cancer. Provided that there are a variety of surgical options available to treat colorectal polyps in patients with adenomatous polyposis, the appropriate surgical option for each patient should be considered. The gold-standard treatment to reduce this risk is prophylactic colectomy, typically by the age of 40. However, colectomy is linked to morbidity and constitutes an ineffective way at preventing extra-colonic disease manifestations, such as desmoid disease, thyroid malignancy, duodenal polyposis, and cancer. Moreover, extensive studies have been conducted into the use of chemopreventive agents to prevent disease progression and delay the necessity for a colectomy as well as the onset of extracolonic disease. The ideal chemoprevention agent should demonstrate a biologically plausible mechanism of action and provide safety, easy tolerance over an extended period of time and a lasting and clinically meaningful effect. Although many pharmaceutical and non-pharmaceutical products have been tested through the years, there has not yet been a chemoprevention agent that meets these criteria. Thus, it is necessary to develop new FAP agents that target novel pathways, such as the mTOR pathway. The aim of this article is to review the prior literature on FAP in order to concentrate the current and future perspectives of diagnosis and treatment. In conclusion, we will provide an update on the diagnostic and therapeutic options, surgical or pharmaceutical, while focusing on the potential treatment strategies that could further reduce the risk of CRC.

Metformin increases pathological responses to rectal cancers with neoadjuvant chemoradiotherapy: a systematic review and meta-analysis

BACKGROUND

To summarize the chemo-radio effect of metformin in rectal cancers with neoadjuvant chemoradiotherapy on pathological response, tumor regression grade (TRG), and T/N downstaging.

METHODS

PubMed, MEDLINE, Embase, and Cochrane Database of collected reviews were searched up to June 30, 2022. This study conducted systematic review and meta-analysis based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) sheet. Odds ratios (ORs) and confidence intervals (CIs) which calculated by random-effects models were displayed in forest plots. Newcastle-Ottawa scale was used to assess the risk of bias of the observational cohort studies.

RESULTS

This systematic review and meta-analysis comprised eight cohorts out of seven studies, with 2294 patients in total. We performed two-way comparison for metformin in diabetic patients vs (1) non-metformin drugs in diabetic patients and (2) nondiabetic patients. In diabetes patient studies, the metformin group had a significantly increased pathological response on TRG (OR: 3.28, CI: 2.01-5.35, I² = 0%, p < 0.001) and T downstaging (OR: 2.14, CI: 1.24-3.67, I² = 14%, p = 0.006) in comparison with a non-metformin group. When compared with nondiabetic patients, the pathological response on TRG (OR: 2.67, CI: 1.65-4.32, I² = 43%, p < 0.001) and T downstaging (OR: 1.96, CI: 1.04-3.71, I² = 66%, p = 0.04) were also higher in metformin group. The limitation was that no randomized controlled trials were available based on current literature review. Small sample sizes for diabetic metformin or non-metformin users in rectal cancer patients reduced the power of the study.

CONCLUSIONS

For patients with rectal cancer and treated with neoadjuvant chemoradiotherapy, metformin administration in diabetic patients increased the pathological response on tumor-regression grade and T downstaging. Further well-designed, high-quality randomized controlled trials are required to reveal the actual effect of metformin.

Colorectal Cancer Chemoprevention: A Dream Coming True?

Colorectal cancer (CRC) is one of the deadliest forms of cancer worldwide. CRC development occurs mainly through the adenoma-carcinoma sequence, which can last decades, giving the opportunity for primary prevention and early detection. CRC prevention involves different approaches, ranging from fecal occult blood testing and colonoscopy screening to chemoprevention. In this review, we discuss the main findings gathered in the field of CRC chemoprevention, focusing on different target populations and on various precancerous lesions that can be used as efficacy evaluation endpoints for chemoprevention. The ideal chemopreventive agent should be well tolerated and easy to administer, with low side effects. Moreover, it should be readily available at a low cost. These properties are crucial because these compounds are meant to be used for a long time in populations with different CRC risk profiles. Several agents have been investigated so far, some of which are currently used in clinical practice. However, further investigation is needed to devise a comprehensive and effective chemoprevention strategy for CRC.

American Association of Clinical Endocrinology Clinical Practice Guideline: Developing a Diabetes Mellitus Comprehensive Care Plan-2022 Update

OBJECTIVE

The objective of this clinical practice guideline is to provide updated and new evidence-based recommendations for the comprehensive care of persons with diabetes mellitus to clinicians, diabetes-care teams, other health care professionals and stakeholders, and individuals with diabetes and their caregivers.

METHODS

The American Association of Clinical Endocrinology selected a task force of medical experts and staff who updated and assessed clinical questions and recommendations from the prior 2015 version of this guideline and conducted literature searches for relevant scientific papers published from January 1, 2015, through May 15, 2022. Selected studies from results of literature searches composed the evidence base to update 2015 recommendations as well as to develop new recommendations based on review of clinical evidence, current practice, expertise, and consensus, according to established American Association of Clinical Endocrinology protocol for guideline development.

RESULTS

This guideline includes 170 updated and new evidence-based clinical practice recommendations for the comprehensive care of persons with diabetes. Recommendations are divided into four sections: (1) screening, diagnosis, glycemic targets, and glycemic monitoring; (2) comorbidities and complications, including obesity and management with lifestyle, nutrition, and bariatric surgery, hypertension, dyslipidemia, retinopathy, neuropathy, diabetic kidney disease, and cardiovascular disease; (3) management of prediabetes, type 2 diabetes with antihyperglycemic pharmacotherapy and glycemic targets, type 1 diabetes with insulin therapy, hypoglycemia, hospitalized persons, and women with diabetes in pregnancy; (4) education and new topics regarding diabetes and infertility, nutritional supplements, secondary diabetes, social determinants of health, and virtual care, as well as updated recommendations on cancer risk, nonpharmacologic components of pediatric care plans, depression, education and team approach, occupational risk, role of sleep medicine, and vaccinations in persons with diabetes.

CONCLUSIONS

This updated clinical practice guideline provides evidence-based recommendations to assist with person-centered, team-based clinical decision-making to improve the care of persons with diabetes mellitus.

Metformin Use Is Inversely Associated with Prevalent, but Not Incident Colorectal Adenomas

BACKGROUND

Chemoprevention for colorectal neoplasia has attracted growing interest, with multiple medications investigated. Metformin may decrease the overall incidence of cancer in patients with diabetes and may decrease the incidence of colorectal cancer.

AIMS

We aimed to determine the impact of metformin use on the behavior of colorectal adenomas in a US veteran population.

METHODS

All patients with at least two high-quality colonoscopies between January 1997 and December 2013 at Veterans Affairs New York Harbor Healthcare System were identified. Outpatient prescription records were used to determine metformin exposure, and colonoscopy findings were recorded. Multivariable logistic regression was used to determine factors associated with adenoma detection on baseline and interval colonoscopy.

RESULTS

In total, 1869 patients with two successive colonoscopies (median 4.5 years) were included. Four hundred and sixty patients had metformin exposure prior to baseline and/or interval colonoscopy. Overall adenoma detection rate was 59.7% at baseline and 45.9% at interval colonoscopy. On multivariable analysis, metformin use was associated with decreased adenoma prevalence at baseline (OR 0.68; 95% CI 0.51-0.92; p = 0.015). Metformin did not impact adenoma incidence at interval colonoscopy whether prescribed before baseline (OR 1.26; 95% CI 0.60-2.67), after baseline (OR 1.25; 95% CI 0.91-1.72), or before and after baseline (OR 1.14; 95% CI 0.82-1.58).

CONCLUSIONS

In this retrospective analysis of an average-risk cohort, metformin use was associated with a decreased prevalence of colorectal adenomas at baseline colonoscopy. This inverse association did not persist on interval colonoscopy. Prospective studies are needed to evaluate potential chemoprotective effects of metformin over time.

Type 2 Diabetes Mellitus and Cancer: Epidemiology, Physiopathology and Prevention

Individuals with type 2 diabetes mellitus are at greater risk of developing cancer and of dying from it. Both diseases are age-related, contributing to the impact of population aging on the long-term sustainability of health care systems in European Union countries. The purpose of this narrative review was to describe, from epidemiological, pathophysiological and preventive perspectives, the links between type 2 diabetes mellitus and the most prevalent cancers in these patients. Multiple metabolic abnormalities that may occur in type 2 diabetes mellitus, particularly obesity, could explain the increased cancer risk. In addition, the effectiveness of drugs commonly used to treat type 2 diabetes mellitus (e.g., metformin and thiazolidinediones) has been broadly evaluated in cancer prevention. Thus, a better understanding of the links between type 2 diabetes mellitus and cancer will help to identify the contributing factors and the pathophysiological pathways and to design personalized preventive strategies. The final goal is to facilitate healthy aging and the prevention of cancer and other diseases related with type 2 diabetes mellitus, which are among the main sources of disability and death in the European Union and worldwide.

Is Metformin Associated With Improved Response to Neoadjuvant Chemoradiotherapy in Locally Advanced Rectal Cancer?

Efforts to determine whether metformin can increase the effectiveness of neoadjuvant chemoradiotherapy in rectal cancer have increased in recent years. However, retrospective studies have yielded inconclusive results.

OBJECTIVES

The aim of this study was to compare oncological outcomes and survival after neoadjuvant chemoradiotherapy in patients with rectal cancer taking metformin versus in those not taking metformin.

METHODS

This study analyzed 423 consecutive patients with locally advanced rectal cancer who underwent neoadjuvant chemoradiotherapy and curative surgery between January 2010 and May 2020; of these, 59 were taking metformin and 364 were not taking metformin.

RESULTS

Patients taking metformin had a lower proportion of tumor regression (6.8% versus 22.0%, P = 0.012) as well as a lower proportion of patients achieving a pathological complete response (6.8% versus 20.6%, P = 0.011). In the multivariate analysis, independent predictors of pathologic complete response were not taking metformin (OR: 5.26, 95% CI: 1.12-24.85, P= 0.035) and cT2 stage (OR: 3.49, 95% CI: 1.10-11.07, P= 0.034); the interval was also an independent predictor of tumor regression (OR: 1.78, 95% CI: 1.06-2.96, P= 0.028). No differences were observed in survival between groups.

CONCLUSION

Metformin was not associated with better tumor responses or survival after neoadjuvant treatment.

Self-reported Metabolic Risk Factor Associations with Adenomatous, Sessile Serrated, and Synchronous Adenomatous and Sessile Serrated Polyps

Studies have found a positive association between metabolic risk factors, such as obesity and diabetes, and adenomatous polyps (AP). However, fewer studies have assessed the association between sessile serrated polyps (SSP) or synchronous diagnosis of APs and SSPs (synch polyps). Study participants (N = 1,370; ages 40-85) undergoing screening colonoscopy were enrolled between August 2016 and February 2020. Self-reported metabolic risk factors, including diabetes, hypertension, hyperlipidemia, and overweight/obesity, were evaluated for associations with new diagnoses of APs, SSPs, and synch polyps at the present colonoscopy. Average participant age was 60.73 ± 8.63 (SD) years; 56.7% were female and 90.9% white. In an assessment of individual metabolic risk factors, adjusted for age, sex, race, and smoking status, increased body mass index (BMI; overweight or obese vs. normal BMI of <25 kg/m2) was associated with an increased odds for new onset of colon APs (P trend < 0.001) as was a diagnosis of diabetes [adjusted conditional OR (aCOR) = 1.59 (1.10-2.29)]. No associations were seen between the metabolic risk factors and onset of SSPs. Being obese or hypertensive each increased the odds of new onset of synch polyps with aCOR values of 2.09 (1.01-4.32) and 1.79 (1.06-3.02), respectively. Self-reported risk factors may help assess polyp type risk. Because SSPs and synch polyps are rare, larger studies are needed to improve our understanding of the contribution of these factors to polyp risk. These data lead us to hypothesize that differences in observed metabolic risk factors between polyp types reflect select metabolic impact on pathways to colorectal cancer. PREVENTION RELEVANCE: Self-reported medical history provides valuable insight into polyp risk, potentially enabling the use of larger retrospective studies of colonoscopy populations to assess knowledge gaps. More aggressive colonoscopy screening, critical to colorectal cancer prevention, may be considered in populations of individuals with metabolic risk factors and modifiable lifestyle risk factors.

The Effect of Metformin in Treatment of Adenomas in Patients with Familial Adenomatous Polyposis

Familial adenomatous polyposis (FAP) is a hereditary disease characterized by the development of numerous colorectal adenomas in young adults. Metformin, an oral diabetic drug, has been shown to have antineoplastic effects and a favorable safety profile. We performed a randomized, double-blind, controlled trial to evaluate the efficacy of metformin on the regression of colorectal and duodenal adenoma in patients with FAP. Thirty-four FAP patients were randomly assigned in a 1:2:2 ratio to receive placebo, 500 mg metformin, or 1,500 mg metformin per day orally for 7 months. The number and size of polyps and the global polyp burden were evaluated before and after the intervention. This study was terminated early based on the results of the interim analysis. No significant differences were determined in the percentage change of colorectal and duodenal polyp number over the course of treatment among the three treatment arms (P = 0.627 and P = 1.000, respectively). We found no significant differences in the percentage change of colorectal or duodenal polyp size among the three groups (P = 0.214 and P = 0.803, respectively). The overall polyp burdens of the colorectum and duodenum were not significantly changed by metformin treatment at either dosage. Colon polyps removed from the metformin-treated patients showed significantly lower mTOR signal (p-S6) expression than those from patients in the placebo arm. In conclusion, 7 months of treatment with 500 mg or 1,500 mg metformin did not reduce the mean number or size of polyps in the colorectum or duodenum in FAP patients (ClinicalTrials.gov ID: NCT01725490). PREVENTION RELEVANCE: A 7-month metformin treatment (500 mg or 1,500 mg) did not reduce the number or size of polyps in the colorectum or duodenum of FAP patients as compared to placebo. These results do not support the use of metformin to promote regression of intestinal adenomas in FAP patients.

Time course and dose effect of metformin on weight in patients with different disease states

OBJECTIVES

The present study was to quantitate and compare the efficacy of metformin on weight in different disease states using model-based meta-analysis (MBMA).

METHODS

Randomized controlled trials (RCT) of metformin effects on weight in different disease states were collected by searching the public databases. The change rate of weight from baseline was selected as the efficacy indicator.

RESULTS

A total 21 RCTs containing 1885 patients including patients with type 2 diabetes mellitus, patients with antipsychotic induced weight gain, patients with obesity, were included into the present study. After deducting placebo effect, the maximal effect (E_max) of metformin on weight in patients with type 2 diabetes mellitus, patients with antipsychotic induced weight gain, patients with obesity were -6.86%, -8.82%, and -4.14%, respectively. The treatment duration to reach half of the maximal effect (ET₅₀) were 107, 45.5, and 15.1 weeks, respectively. Within the metformin dose range from 21 RCTs, no significant dose-response relationship was observed. However, the time-course relationship is obvious for efficacy of metformin on weight.

CONCLUSIONS

The present study firstly provided quantitative information for metformin effects on weight in different disease states, including patients with type 2 diabetes mellitus, patients with antipsychotic induced weight gain, patients with obesity.

Use of metformin and risk of breast and colorectal cancer

BACKGROUND

Diabetes has been associated with increased risk of cancer, including breast cancer and colorectal cancer. Metformin, an oral hypoglycemic drug, but not other anti-diabetic drugs, has been associated with reduced risk of breast and of colon cancers in some, but not in other, studies.

METHODS

Data from two large-scale, population-based, case-control studies of breast and colorectal cancers etiology, conducted in Northern Israel since 1998 were analyzed to evaluate the association between regular use (>3 times) of metformin prior to diagnosis and risk of developing cancer. The multivariate analyses for both cancer sites included age, family history of breast/colorectal cancer, history of diabetes, sports participation, fruits/vegetables consumption, aspirin and statins use, and for breast cancer, also included use of oral contraceptives and postmenopausal hormones and number of pregnancies. Use of metformin and diabetes status were determined based on valid electronic medical records of the participants.

RESULTS

Metformin use prior to diagnosis of cancer was associated with a decrease in risk of both breast cancer (OR = 0.821, 0.726-0.928, p = 0.002) and colorectal cancer (OR = 0.754, 0.623-0.912, p = 0.004). An inverse association was not identified with use of other anti-diabetic medications. Diabetes was found to be associated with risk of colorectal cancer (OR = 1.204, 1.014-1.431, p = 0.034) but not of breast cancer. No dose response by years of use of metformin was found.

CONCLUSION

These analyses of large population-based studies provide evidence of a strong inverse association of metformin with breast and, even more so, with colorectal cancer risk.

Chemoprevention of Colorectal Cancer

Although colorectal cancer (CRC) screening has reduced the incidence of and mortality from CRC, chemoprevention strategies have the potential to further reduce CRC incidence and mortality. Chemoprevention agents might be used for average-risk as well as high-risk groups, and to prevent CRC recurrence after therapy. CRC chemoprevention agents that have been studied include aspirin, nonaspirin nonsteroidal anti-inflammatory drugs, statins, agents that target metabolic pathways, and vitamins and minerals. We review the prospect of chemoprevention of CRC, results from preclinical and human studies, challenges, and future directions.

Metformin in colorectal cancer: molecular mechanism, preclinical and clinical aspects

Growing evidence showed the increased prevalence of cancer incidents, particularly colorectal cancer, among type 2 diabetic mellitus patients. Antidiabetic medications such as, insulin, sulfonylureas, dipeptyl peptidase (DPP) 4 inhibitors and glucose-dependent insulinotropic peptide (GLP-1) analogues increased the additional risk of different cancers to diabetic patients. Conversely, metformin has drawn attention among physicians and researchers since its use as antidiabetic drug exhibited beneficial effect in the prevention and treatment of cancer in diabetic patients as well as an independent anticancer drug. This review aims to provide the comprehensive information on the use of metformin at preclinical and clinical stages among colorectal cancer patients. We highlight the efficacy of metformin as an anti-proliferative, chemopreventive, apoptosis inducing agent, adjuvant, and radio-chemosensitizer in various colorectal cancer models. This multifarious effects of metformin is largely attributed to its capability in modulating upstream and downstream molecular targets involved in apoptosis, autophagy, cell cycle, oxidative stress, inflammation, metabolic homeostasis, and epigenetic regulation. Moreover, the review highlights metformin intake and colorectal cancer risk based on different clinical and epidemiologic results from different gender and specific population background among diabetic and non-diabetic patients. The improved understanding of metformin as a potential chemotherapeutic drug or as neo-adjuvant will provide better information for it to be used globally as an affordable, well-tolerated, and effective anticancer agent for colorectal cancer.

Suppressive effects of metformin on colorectal adenoma incidence and malignant progression

BACKGROUND

The linear progression from normal colonic epithelium to adenoma initiation, carcinoma transformation and metastasis is considered the classical model of colorectal cancer (CRC) development. Although metformin has been extensively reported to be negatively related to cancer incidence, the effect of metformin on CRC development remains unclear. We aimed to evaluate the role of metformin in the entire CRC linear progression.

METHODS

Systematic searches and data extraction were performed in the PubMed, Embase, and Cochrane Library databases on Jan 31, 2019. The combined relative ratios (RRs) of colorectal tumor incidence and the hazard ratios (HRs) of overall survival (OS) and cancer-specific survival (CSS) were evaluated by a random-effects model. Then, the effects of metformin were further assessed through stratified analyses by population, medication duration and dosage, dose-response analysis and comparison with other antidiabetic agents.

RESULTS

A total of 50 studies consisting of 238,540 cases of diabetes mellitus (DM) were included in this study. Metformin use was negatively associated with the incidence of colorectal adenoma (RR: 0.75, 95% CI: 0.65-0.86) and CRC (RR: 0.73, 95% CI: 0.58-0.90). Moreover, CRC patients benefited from metformin in terms of both OS (HR: 0.73, 95% Cl: 0.63-0.84) and CSS (HR: 0.60, 95% Cl: 0.50-0.73). Stratified analyses suggested that a long duration of high-dose metformin (RR: 0.52, 95% Cl: 0.36-0.83) was more effective than a short duration in Asian populations against colorectal adenoma (RR: 0.66, 95% Cl: 056-0.70) and CRC (RR: 0.45, 95% Cl: 0.29-0.70). Interestingly, metformin use decreased CRC risk in a dose-dependent manner (RR: 0.91, 95% CI: 0.87-0.95). In addition, the benefit of metformin on CRC was more significant than that of other antidiabetic agents, including insulin.

CONCLUSIONS

The use of metformin is associated with a lower incidence of adenoma and CRC and a better prognosis, especially in Asian populations.

Difference in Physician- and Patient-Dependent Factors Contributing to Adenoma Detection Rate and Serrated Polyp Detection Rate

BACKGROUND

Adenoma detection rate (ADR) is correlated with the risk of interval colorectal cancer and is considered as a quality benchmark for colonoscopy. Serrated polyp detection rate (SPDR) might be a more stringent indicator of quality in polyp detection.

AIMS

To evaluate in a 2-year monocentric observational study patient-dependent and endoscopist-dependent factors influencing ADR and SPDR in daily practice.

METHODS

We determined ADR and SPDR. We collected patient-dependent factors and endoscopist-dependent factors. Links between these data and detection rates were assessed by uni- and multivariate analysis.

RESULTS

A total of 11682 colonoscopies were performed (female: 54.3%; male: 45.7%; median age 58) by 30 endoscopists (female: 9; male: 21). ADR and SPDR were 29.2% and 8%, respectively. In multivariate analysis, ADR was associated with patient-dependent factors: age (OR 1.044, CI 95% 1.040-1.048), male gender (OR 1.7, CI 95% 1.56-1.85), personal history of polyp/cancer (OR 1.53, CI 95% 1.3-1.9), and positive fecal immunochemical test (OR 2.47, CI 95% 2.0-3.1). In multivariate analysis, SPDR was associated with withdrawal time (OR 1.25, CI 95% 1.17-1.32), low volume activity (OR 1.3, CI 95% 1.1-1.52), and personal history of polyp/cancer (OR 1.61, CI 95% 1.15-2.25).

CONCLUSION

In this large series of routine colonoscopies, we found that ADR was mainly driven by patient-dependent conditions, i.e., age, male gender, colonoscopy indication for positive FIT, and a personal history of polyp or cancer. In contrast, SPDR was mainly related to endoscopist-dependent factor, i.e., withdrawal time and low volume activity.

Lifestyle and dietary environmental factors in colorectal cancer susceptibility

Colorectal cancer (CRC) incidence changes with time and by variations in diet and lifestyle, as evidenced historically by migrant studies and recently by extensive epidemiologic evidence. The worldwide heterogeneity in CRC incidence is strongly suggestive of etiological involvement of environmental exposures, particularly lifestyle and diet. It is established that physical inactivity, obesity and some dietary factors (red/processed meats, alcohol) are positively associated with CRC, while healthy lifestyle habits show inverse associations. Mechanistic evidence shows that lifestyle and dietary components that contribute to energy excess are linked with increased CRC via metabolic dysfunction, inflammation, oxidative stress, bacterial dysbiosis and breakdown of gut barrier integrity while the reverse is apparent for components associated with decreased risk. This chapter will review the available evidence on lifestyle and dietary factors in CRC etiology and their underlying mechanisms in CRC development. This short review will also touch upon available information on potential gene-environment interactions, molecular sub-types of CRC and anatomical sub-sites within the colorectum.

Therapeutic cancer prevention: achievements and ongoing challenges - a focus on breast and colorectal cancer

The constant increase of cancer incidence and the huge costs of new treatments make cancer prevention a crucial goal in order to maintain sustainable public health systems across the world. Carcinogenesis is a multistep process, which allows time for active intervention with natural or synthetic agents to stop or reverse the pathological process. Cancer prevention medicine can be considered to be treatment of premalignant cells or preneoplastic conditions. Clearly such interventions require well‐defined risk classification so that personalized strategies and specific treatments can be applied to cohorts with a documented increased cancer risk, and not to the general population as a whole. Further development of these strategies in an efficient and timely manner requires investment in the discovery and validation of surrogate cancer biomarkers with both prognostic and predictive value to detect and monitor the efficacy of interventions in clinical trials and beyond. In the field of cancer prevention medicine, breast and colon cancer demonstrates the strongest clinical evidence that pharmacological intervention can lower cancer risk. Here, we offer an overview of the major clinical achievements for these cancers and the critical issues to improve implementation and clinical uptake of efficacious therapies, as well as further developments needed in the field of preventive medicine.

Metformin in cancer

Metformin is a lipophilic biguanide which inhibits hepatic gluconeogenesis and improves peripheral utilization of glucose. It is the first line pharmacotherapy for glucose control in patients with Type 2 diabetes due to its safety, efficacy and tolerability. Metformin exhibits pleotropic effects, which may have beneficial effects on a variety of tissues independent of glucose control. A potential anti-tumourigenic effect of metformin may be mediated by its role in activating AMP-kinase, which in turn inhibits mammalian target of rapamycin (mTOR). Non-AMPK dependent protective pathways may include reduction of insulin, insulin-like growth factor-1, leptin, inflammatory pathways and potentiation of adiponectin, all of which may have a role in tumourigenesis. A role in inhibiting cancer stem cells is also postulated. A number of large scale observational and cohort studies suggest metformin is associated with a reduced risk of a number of cancers, although the data is not conclusive. Recent randomised studies reporting use of metformin in treatment of cancer have revealed mixed results, and the results of much larger randomised trials of metformin as an adjuvant therapy in breast and colorectal cancers are awaited.

Cancer cell specific inhibition of Wnt/β-catenin signaling by forced intracellular acidification

Use of the diabetes type II drug Metformin is associated with a moderately lowered risk of cancer incidence in numerous tumor entities. Studying the molecular changes associated with the tumor-suppressive action of Metformin we found that the oncogene SOX4, which is upregulated in solid tumors and associated with poor prognosis, was induced by Wnt/β-catenin signaling and blocked by Metformin. Wnt signaling inhibition by Metformin was surprisingly specific for cancer cells. Unraveling the underlying specificity, we identified Metformin and other Mitochondrial Complex I (MCI) inhibitors as inducers of intracellular acidification in cancer cells. We demonstrated that acidification triggers the unfolded protein response to induce the global transcriptional repressor DDIT3, known to block Wnt signaling. Moreover, our results suggest that intracellular acidification universally inhibits Wnt signaling. Based on these findings, we combined MCI inhibitors with H⁺ ionophores, to escalate cancer cells into intracellular hyper-acidification and ATP depletion. This treatment lowered intracellular pH both in vitro and in a mouse xenograft tumor model, depleted cellular ATP, blocked Wnt signaling, downregulated SOX4, and strongly decreased stemness and viability of cancer cells. Importantly, the inhibition of Wnt signaling occurred downstream of β-catenin, encouraging applications in treatment of cancers caused by APC and β-catenin mutations.

Molecular mechanisms of the preventable causes of cancer in the United States

Annually, there are 1.6 million new cases of cancer and nearly 600,000 cancer deaths in the United States alone. The public health burden associated with these numbers has motivated enormous research efforts into understanding the root causes of cancer. These efforts have led to the recognition that between 40% and 45% of cancers are associated with preventable risk factors and, importantly, have identified specific molecular mechanisms by which these exposures modify human physiology to induce or promote cancer. The increasingly refined knowledge of these mechanisms, which we summarize here, emphasizes the need for greater efforts toward primary cancer prevention through mitigation of modifiable risk factors. It also suggests exploitable avenues for improved secondary prevention (which includes the development of therapeutics designed for cancer interception and enhanced techniques for noninvasive screening and early detection) based on detailed knowledge of early neoplastic pathobiology. Such efforts would complement the current emphasis on the development of therapeutic approaches to treat established cancers and are likely to result in far greater gains in reducing morbidity and mortality.

Pushing the Limits of Cancer Therapy: The Nutrient Game

The standard cancer treatments include chemotherapy, radiotherapy, or their combination, which are generally associated with a multitude of side effects ranging from discomfort to the development of secondary tumors and severe toxicity to multiple systems including immune system. Mounting evidence has highlighted that the fine-tuning of nutrients may selectively sensitize cancer cells to conventional cancer therapies, while simultaneously protecting normal cells from their side effects. Nutrient modulation through diet also improves cancer immunesurveillance in a way that severe immunosuppression could be avoided or even the immune response or immune-based cancer therapies be potentiated also through patient microbiota remodeling. Here, we review recent advances in cancer therapy focusing on the effects of adjuvant dietary interventions (e.g., ketogenic diets, fasting) on the metabolic pathways within cancer cells and tumor environment (e.g., microbiota, immune system, tumor microenvironment) that are involved in cancer progression and resistance as well as cancer cell death. Finally, based on the overall literature data, we designed a nutritional intervention consisting in a plant-based moderate ketogenic diet that could be exploited for future preclinical research in cancer therapy.

Adenomas - Genetic factors in colorectal cancer prevention

Colorectal cancer is the second most common type of cancer both in Europe and Poland. During the last 30 years more than a 3-fold increase has been observed in Poland due to environmental and genetic factors. Almost all colorectal malignancies are related to the formation and malignant transformation of colorectal dysplasia and adenoma. Efforts aiming to decrease the number of colorectal cancer deaths are focused on the disease early detection. Genetic diagnosis for hereditary syndromes predisposing to colorectal cancer has been developed and is a part of the routine treatment. Most cancers are sporadic. They often develop from polyps in the colon. In addition to the genetic events described in the 1990s, showing the adenoma transformation into carcinoma that has been a prime example of malignant transformation for a long time, there are also other possibilities of neoplastic transformation. The recognition of colorectal cancer risk factors make sense as their nature is lifestyle- and diet-related. In this review paper those risk factors are presented and the prevention of colorectal cancer is discussed taking into account genetic factors.

Different effects of metformin and insulin on primary and secondary chemoprevention of colorectal adenoma in diabetes type 2: Traditional and Bayesian meta-analysis

Metformin and insulin differently affect the risk of colon cancer in type 2 diabetic patients, however their effects on colon adenoma is not clear. PubMed, ISI, Scopus and Cochrane databases were searched for studies reporting. The outcomes were total adenoma; advanced adenoma and recurrent adenoma. Traditional and Bayesian meta-analysis were conducted via random-effects models. Odds ratios (OR) with 95 % confidence intervals (CIs) / or credible intervals (CrI) were used to describe the ratio of different events. A random-effects model described by DerSimonian and Laird was performed, when significant between-study heterogeneity existed. Alternatively, an inverse variance fixed effects model was used, when there was no significant heterogeneity across studies. The potential publication bias was assessed with funnel plot, Egger and Begg's regression asymmetry tests. Moreover, “trim and fill” procedure was used to assess the possible effect of publication bias. For metformin intake, 11 studies (51991 patients) were included. The results showed that metformin significantly decreased the risk of advance adenoma (OR= 0.51, p< 0.001). The risk of total adenoma was not associated with metformin use (OR= 0.86, p=0.274), and metformin did not affect the risk of adenoma recurrence (OR= 0.89, p=0.137). Five studies (2678 patients) were included in the analysis to determine the effect of insulin therapy. Insulin significantly increased the risk of colorectal adenoma (OR= 1.43, p=0.002). These findings indicate that metformin has no protective effect on total and recurrent adenoma, whilst it significantly reduces the risk of advanced adenoma, but insulin increases the risk of total adenoma.

Repurposing metformin for the prevention of cancer and cancer recurrence

Multiple epidemiological studies have documented an association between metformin, used for treatment of type 2 diabetes, and reduced cancer incidence and mortality. Cell line models may not accurately reflect the effects of metformin in the clinical setting. Moreover, findings from animal model studies have been inconsistent, whilst those from more recent epidemiological studies have tempered the overall effect size. The purpose of this review is to examine metformin's chemopreventive potential by outlining relevant mechanisms of action, the most recent epidemiologic evidence, and recently completed and ongoing clinical trials. Although repurposing drugs with excellent safety profiles is an appealing strategy for cancer prevention and treatment in the adjuvant setting, there is no substitute for well-executed, large randomised clinical trials to define efficacy and determine the populations that are most likely to benefit from an intervention. Thus, enthusiasm remains for understanding the role of metformin in cancer through ongoing clinical research.