Does metformin affect the incidence of colonic polyps and adenomas in patients with type 2 diabetes mellitus?

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.

Is Metformin Associated with a Lower Prevalence of Polyps, Adenomas, and Colorectal Carcinoma in Patients with Diabetes Mellitus?

PURPOSE

Recent studies suggested a protective role of metformin in the development of colorectal cancer (CRC) and its precursors. We aimed to investigate if metformin was associated with a lower prevalence and number of colorectal polyps in diabetic patients and also adenomas, high-risk adenomas, and CRC.

METHODS

Retrospective study on adult patients with diabetes mellitus followed in our hospital with a total colonoscopy between 2015 and 2019, treated with either metformin for > 5 years or other antidiabetic agent (control group). We assessed the number, size, and histopathology examination of proliferative lesions detected on colonoscopy.

RESULTS

We included 401 patients aged 69 ± 9 years, 57% males, divided into two groups: treated with metformin (n = 260) and without (n = 141). The number of polyps detected was significantly lower in patients under metformin (p = 0.014). There was a nonsignificant trend towards lower polyp detection rates in the metformin compared to the control group both in unadjusted analysis (50% vs 60%, p = 0.058) and multivariable adjusted analysis (odds ratio [OR] 0.68, 95% confidence interval [CI] 0.43-1.09, p = 0.111). In the latter, we identified male gender (OR 2.24, 95%CI 1.44-3.49, p < 0.001), age (OR 1.35 for every 10 years, 95%CI 1.07-1.71, p = 0.012), glycated hemoglobin value (OR 1.20 for every 1% increase, 95%CI 1.06-1.37, p = 0.005), and hypertension (OR 1.76, 95%CI 1.01-3.08, p = 0.046) as factors associated with a higher prevalence of polyps. We saw no statistically significant differences regarding adenoma (p = 0.231), high-risk adenoma (p = 0.810), and CRC (p = 0.705) diagnoses between groups.

CONCLUSION

In our study, metformin was associated with less colorectal polyps in diabetic patients compared to other treatment modalities. We observed a nonsignificant trend towards lower polyp detection rates in the metformin group both in unadjusted and adjusted analyses.

Effect of metformin on thyroid cancer risk in patients with acromegaly: A preliminary observational study

PURPOSE

To evaluate the role of metformin on thyroid cancer risk in patients with acromegaly.

METHODS

Medical charts of 534 patients with acromegaly that were followed-up between 1983 and 2019 were reviewed. Patients with follow-up duration at least 6 months were included. Cohort entry was defined as first visit date. The date of each case's thyroid cancer diagnosis was defined as index date. Patients were followed until the index date, death, or last visit date, whichever came first. Nested case-control study design was selected to evaluate the association between metformin and the thyroid cancer risk in patients with acromegaly.

RESULTS

291 patients with acromegaly were included into final analysis. The mean age at acromegaly diagnosis was 42.3 ± 1.3 years. The median follow-up duration was 76 [34-132] months. Among 291 patients, 13 patients (4.5%) had thyroid cancer. Thirty-one percent (n = 92) of the patients used metformin for 6 months or longer. One standard deviation (SD) increase in average growth hormone increased the odds of having thyroid cancer by 1.164 folds (p = 0.017). One SD increase of the average insulin-like growth factor 1 to upper limit of normal ratio increased the odds of having thyroid cancer by 1.201 folds (p = 0.004). If a patient used metformin for at least 6 months, the odds to have thyroid cancer was decreased, multiplied by 0.62 with a 95% confidence interval of [0.47, 0.83] (p = 0.0013). The risk of thyroid cancer decreased with increasing duration of metformin use.

CONCLUSION

Metformin may decrease the thyroid cancer risk in patients with acromegaly.

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.

Bovine Meat and Milk Factors (BMMFs): Their Proposed Role in Common Human Cancers and Type 2 Diabetes Mellitus

Simple Summary

This manuscript emphasizes the mechanistic differences of infectious agents contributing to human cancers either by “direct” or “indirect” interactions. The epidemiology of cancers linked to direct carcinogens differs (e.g., response to immunosuppression) from those cancers linked with indirect infectious interactions. We discuss their role in colon, breast, and prostate cancers and type II diabetes mellitus. A brief discussion covers the potential role of BMMF (bovine meat and milk factor) infections in acute myeloid leukemia.

Abstract

Exemplified by infections with bovine meat and milk factors (BMMFs), this manuscript emphasizes the different mechanistic aspects of infectious agents contributing to human cancers by “direct” or “indirect” interactions. The epidemiology of cancers linked to direct carcinogens (e.g., response to immunosuppression) differs from those cancers linked with indirect infectious interactions. Cancers induced by direct infectious carcinogens commonly increase under immunosuppression, whereas the cancer risk by indirect carcinogens is reduced. This influences their responses to preventive and therapeutic interferences. In addition, we discuss their role in colon, breast and prostate cancers and type II diabetes mellitus. A brief discussion covers the potential role of BMMF infections in acute myeloid leukemia.

Metformin Modifies the Gut Microbiota of Mice Infected with Helicobacter pylori

Metformin is widely prescribed to treat type 2 diabetes. Diabetes patients treated with metformin have a decreased risk of cancers, including gastric cancer. Among the factors influencing digestive carcinogenesis, gut microbiota interactions have been intensively studied. Metformin exhibits direct antimicrobial activity toward Helicobacterpylori, which plays a crucial role in gastric carcinogenesis. Mice were infected with H. pylori and treated for 12 days with either metformin or phosphate-buffered saline (PBS) as a control. At the end of the treatment period, the mice were euthanized and cecal and intestinal contents and stool were collected. The gut microbiota of the three different digestive sites (stool, cecal, and intestinal contents) were characterized through 16S RNA gene sequencing. In mice infected with H. pylori, metformin significantly decreased alpha diversity indices and led to significant variation in the relative abundance of some bacterial taxa including Clostridium and Lactobacillus, which were directly inhibited by metformin in vitro. PICRUSt analysis suggested that metformin modifies functional pathway expression, including a decrease in nitrate reducing bacteria in the intestine. Metformin significantly changed the composition and predicted function of the gut microbiota of mice infected with H. pylori; these modifications could be implicated in digestive cancer prevention.

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.

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.

Diabetes Mellitus and Colon Carcinogenesis: Expectation for Inhibition of Colon Carcinogenesis by Oral Hypoglycemic Drugs

The global deaths due to colorectal cancer and diabetes mellitus have increased by 57% and 90%, respectively. The relationship between various cancers and diabetes mellitus has been shown in multiple epidemiological studies. Hence, better management of diabetes mellitus is expected to reduce the risk of various cancers. This review focuses on colorectal cancer and aims to summarize recent findings on the antitumor effects of various oral hypoglycemic drugs on colorectal cancer and their estimated mechanisms. Of the seven classes of oral hypoglycemic agents, only metformin was found to have suppressive effects on colorectal cancer in both clinical and basic research. Clinical and basic researches on suppressing effects of glinides, dipeptidyl peptidase-4 inhibitors, thiazolidinedione, α-glucosidase inhibitors, and sodium glucose cotransporter-2 inhibitors against colon carcinogenesis have been insufficient and have not arrived at any conclusion. Therefore, further research regarding these agents is warranted. In addition, the suppressive effects of these agents in healthy subjects without diabetes should also be investigated.

Postoperative adjuvant chemotherapy is associated with a lower incidence of colorectal adenomas in patients with previous colorectal cancer

BACKGROUND AND AIMS

The effects of chemotherapeutic agents on the development of colorectal adenomas in patients with previous colorectal cancer (CRC) are not defined. Therefore, we evaluated the potential effect of adjuvant chemotherapy on the incidence of colorectal adenomas in patients with previous CRC.

METHODS

We selected patients with low-risk stage II CRC with or without postoperative 5-fluorouracil-based adjuvant chemotherapy to reduce selection bias. Among 1808 patients with stage II CRC who underwent colonoscopic surveillance after curative resection of CRC between 2006 and 2013, 192 patients were retrospectively enrolled in this study after matching for age and sex. The patients were divided into 96 patients receiving and 96 patients not receiving 5-fluorouracil-based chemotherapy.

RESULTS

Forty patients (41.7%) exhibited colorectal adenomas among 96 patients who received adjuvant chemotherapy, compared with 50 patients (52.1%) with colorectal adenomas among 96 patients who received surgery only. The incidence rate of advanced adenoma was significantly lower in the chemotherapy group than in the nonchemotherapy group (3.1% vs 10.4%, P = .044). After adjustment for clinically relevant factors such as body mass index, aspirin use, metformin use, number of follow-up colonoscopies, and operation type, adjuvant chemotherapy was found to be associated with a decreased incidence of advanced adenoma (odds ratio, .151; 95% confidence interval, .035-.653; P = .011) in patients with stage II CRC.

CONCLUSIONS

The results showed that chemotherapy in patients with CRC may be associated with a lower risk of colorectal advanced adenoma development.

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.

Therapeutic strategies against cancer stem cells in human colorectal cancer

Colorectal cancer (CRC) is the third most frequent malignancy and represents the fourth most common cause of cancer-associated mortalities in the world. Despite many advances in the treatment of CRC, the 5-year survival rate of patients with CRC remains unsatisfactory due to tumor recurrence and metastases. Recently, cancer stem cells (CSCs), have been suggested to be responsible for the initiation and relapse of the disease, and have been identified in CRC. Due to their basic biological features, which include self-renewal and pluripotency, CSCs may be novel therapeutic targets for CRC and other cancer types. Conventional therapeutics only act on proliferating and mature cancer cells, while quiescent CSCs survive and often become resistant to chemotherapy. In this review, markers of CRC-CSCs are evaluated and the recently introduced experimental therapies that specifically target these cells by inducing CSC proliferation, differentiation and sensitization to apoptotic signals via molecules including Dickkopf-1, bone morphogenetic protein 4, Kindlin-1, tankyrases, and p21-activated kinase 1, are discussed. In addition, novel strategies aimed at inhibiting some crucial processes engaged in cancer progression regulated by the Wnt, transforming growth factor β and Notch signaling pathways (pyrvinium pamoate, silibinin, PRI-724, P17, and P144 peptides) are also evaluated. Although the metabolic alterations in cancer were first described decades ago, it is only recently that the concept of targeting key regulatory molecules of cell metabolism, such as sirtuin 1 (miR-34a) and AMPK (metformin), has emerged. In conclusion, the discovery of CSCs has resulted in the definition of novel therapeutic targets and the development of novel experimental therapies for CRC. However, further investigations are required in order to apply these novel drugs in human CRC.

Metformin therapy and risk of colorectal adenomas and colorectal cancer in type 2 diabetes mellitus patients: A systematic review and meta-analysis

Recent evidence indicates that metformin therapy may be associated with a decreased colorectal adenoma/colorectal cancer risk in type 2 diabetes patients. However, results are not consistent. We therefore performed a systematic review and meta-analysis to assess the association between metformin therapy and risk of colorectal adenomas/colorectal cancer in type 2 diabetes mellitus patients. We searched the literature published before Aug 31, 2016 in four databases: PubMed, Embase database, CNKI and VIP Library of Chinese Journal. Summary risk estimates (adjusted OR/adjusted RR/adjusted HR) with their 95% confidence interval (95% CI) were obtained using a random effects model. Twenty studies (including 12 cohort studies, 7 case-control studies and 1 randomized controlled trial study) were selected in terms of data of colorectal adenomas or colorectal cancer incidence. Metformin therapy was found to be associated with a decreased incidence of colorectal adenomas (unadjusted OR=0.80, 95% CI: 0.71-0.90, p=0.0002). When the adjusted data were analyzed, the summary estimate decreased to 25% reduction in colorectal adenomas risk (adjusted OR=0.75, 95% CI: 0.59-0.97, p=0.03). Besides, a significant reduction of colorectal cancer risk was also observed (unadjusted OR=0.73, 95% CI: 0.62-0.86, p=0.0002). And when the adjusted data were analyzed, colorectal cancer risk for metformin users was decreased with a reduction of 22%, compared with non-metformin users and other treatment users (adjusted OR=0.78, 95% CI: 0.70-0.87, p<0.00001). Our meta-analysis suggested that metformin therapy may be associated with a decreased risk of colorectal adenomas and colorectal cancer in type 2 diabetes mellitus patients.

Energy sensing pathways: Bridging type 2 diabetes and colorectal cancer?

The recently rapid increase of obesity and type 2 diabetes mellitus has caused great burden to our society. A positive association between type 2 diabetes and risk of colorectal cancer has been reported by increasing epidemiological studies. The molecular mechanism of this connection remains elusive. However, type 2 diabetes may result in abnormal carbohydrate and lipid metabolism, high levels of circulating insulin, insulin growth factor-1, and adipocytokines, as well as chronic inflammation. All these factors could lead to the alteration of energy sensing pathways such as the AMP activated kinase (PRKA), mechanistic (mammalian) target of rapamycin (mTOR), SIRT1, and autophagy signaling pathways. The resulted impaired SIRT1 and autophagy signaling pathway could increase the risk of gene mutation and cancer genesis by decreasing genetic stability and DNA mismatch repair. The dysregulated mTOR and PRKA pathway could remodel cell metabolism during the growth and metastasis of cancer in order for the cancer cell to survive the unfavorable microenvironment such as hypoxia and low blood supply. Moreover, these pathways may be coupling metabolic and epigenetic alterations that are central to oncogenic transformation. Further researches including molecular pathologic epidemiologic studies are warranted to better address the precise links between these two important diseases.

Diabetes-induced mechanophysiological changes in the small intestine and colon

The disorders of gastrointestinal (GI) tract including intestine and colon are common in the patients with diabetes mellitus (DM). DM induced intestinal and colonic structural and biomechanical remodeling in animals and humans. The remodeling is closely related to motor-sensory abnormalities of the intestine and colon which are associated with the symptoms frequently encountered in patients with DM such as diarrhea and constipation. In this review, firstly we review DM-induced histomorphological and biomechanical remodeling of intestine and colon. Secondly we review motor-sensory dysfunction and how they relate to intestinal and colonic abnormalities. Finally the clinical consequences of DM-induced changes in the intestine and colon including diarrhea, constipation, gut microbiota change and colon cancer are discussed. The final goal is to increase the understanding of DM-induced changes in the gut and the subsequent clinical consequences in order to provide the clinicians with a better understanding of the GI disorders in diabetic patients and facilitates treatments tailored to these patients.

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

BACKGROUND AND AIM

Although it is known that metformin can reduce risk of colorectal cancer, it is unclear whether it protects against colorectal adenoma.

METHODS

This study conducted a systematic literature search on MEDLINE, EMBASE, and the Cochrane Library using the primary keywords "colorectal," "colon," "rectal," "rectum," "adenoma," "polyp," "neoplasia," "neoplasm," "metformin," and "diabetes." Studies were included if they evaluated the association between metformin use and colorectal adenoma and reported odds ratios (ORs) or provided data from which these could be estimated.

RESULTS

Ten studies and a total of 8726 patients were evaluated. Across all studies, a median of 32.1% (range: 15.2-53.0%) of patients taking metformin also had adenoma; a median of 43.5% (range: 20.5-59.6%) of those not taking metformin had adenoma. In our meta-analysis, metformin use reduced the risk of adenoma (pooled OR = 0.76, 95% confidence interval [CI] = 0.63-0.92, I²  = 60%). Upon subgroup analyses, metformin use tended to reduce risk of adenoma in a high-risk population consisting of patients with a history of colorectal neoplasia (CRN) (pooled OR = 0.61, 95% CI = 0.34-1.10, I²  = 79%). In addition, metformin reduced the risk of adenoma in a high-risk population consisting of patients with diabetes mellitus (pooled OR = 0.75, 95% CI = 0.62-0.91, I²  = 57%).

CONCLUSION

Metformin use seemed to be associated with a reduced risk of colorectal adenoma, especially in high-risk populations consisting of patients with diabetes mellitus or a history of CRN, although statistical power was not achieved in patients with a history of CRN.

Parameters of Glucose and Lipid Metabolism Affect the Occurrence of Colorectal Adenomas Detected by Surveillance Colonoscopies

PURPOSE

Limited data are available regarding the associations between parameters of glucose and lipid metabolism and the occurrence of metachronous adenomas. We investigated whether these parameters affect the occurrence of adenomas detected on surveillance colonoscopy.

MATERIALS AND METHODS

This longitudinal study was performed on 5289 subjects who underwent follow-up colonoscopy between 2012 and 2013 among 62171 asymptomatic subjects who underwent an initial colonoscopy for a health check-up between 2010 and 2011. The risk of adenoma occurrence was assessed using Cox proportional hazards modeling.

RESULTS

The mean interval between the initial and follow-up colonoscopy was 2.2±0.6 years. The occurrence of adenomas detected by the follow-up colonoscopy increased linearly with the increasing quartiles of fasting glucose, hemoglobin A1c (HbA1c), insulin, homeostasis model assessment of insulin resistance (HOMA-IR), and triglycerides measured at the initial colonoscopy. These associations persisted after adjusting for confounding factors. The adjusted hazard ratios for adenoma occurrence comparing the fourth with the first quartiles of fasting glucose, HbA1c, insulin, HOMA-IR, and triglycerides were 1.50 [95% confidence interval (CI), 1.26-1.77; p(trend)<0.001], 1.22 (95% CI, 1.04-1.43; p(trend)=0.024), 1.22 (95% CI, 1.02-1.46; p(trend)=0.046), 1.36 (95% CI, 1.14-1.63; p(trend)=0.004), and 1.19 (95% CI, 0.99-1.42; p(trend)=0.041), respectively. In addition, increasing quartiles of low-density lipoprotein-cholesterol and apolipoprotein B were associated with an increasing occurrence of adenomas.

CONCLUSION

The levels of parameters of glucose and lipid metabolism were significantly associated with the occurrence of adenomas detected on surveillance colonoscopy. Improving the parameters of glucose and lipid metabolism through lifestyle changes or medications may be helpful in preventing metachronous adenomas.

Metformin therapy and the risk of colorectal adenoma in patients with type 2 diabetes: A meta-analysis

BACKGROUND

Existing data evaluating the impact of metformin on the colorectal adenoma (CRA) risk in patients suffering from type 2 diabetes (T2D) are limited and controversial. We therefore summarized the studies currently available and assessed the relationship between metformin treatment and risk of CRA in T2D patients.

METHODS

We systematically searched databases for eligible studies that explored the impact of metformin treatment on the occurrence of CRA in T2D patients from inception to June 2016. The summary odds ratio (OR) estimates with their 95% confidence interval (CI) were derived using random-effect, generic inverse variance methods. Sensitivity analysis and subgroup analysis were performed.

RESULTS

Seven studies involving 7178 participants met the inclusion criteria. The pooling showed that metformin therapy has a 27% decrease in the CRA risk (OR, 0.73; 95% CI, 0.58 - 0.90). In subgroup analysis, we detected that metformin exhibits significant chemoprevention effects in Asia region (OR, 0.68; 95% CI, 0.48 - 0.96). Similar results were identified in both studies with adjusted ORs and high-quality studies (OR, 0.66; 95% CI, 0.50 - 0.86 and OR, 0.70; 95% CI, 0.58 - 0.84, respectively). Of note, an inverse relationship was noted that metformin therapy may result in a significant decrease in the advanced adenoma risk (OR, 0.52; 95% CI, 0.38 - 0.72). Low heterogeneity was observed, however, the results remained robust in multiple sensitivity analyses.

CONCLUSIONS

This meta-analysis indicates that metformin therapy is correlated with a significant decrease in the risk of CRA and advanced adenoma in T2D patients. Further confirmatory studies are warranted.

Potential Benefit of Metformin as Treatment for Colon Cancer: the Evidence so Far

Metformin is known as a hypoglycaemic agent that regulates glucose homeostasis by inhibiting liver glucose production and increasing muscle glucose uptake. Colorectal cancer (CRC) is one of the most common cancers worldwide, with about a million new cases diagnosed each year. The risk factors for CRC include advanced age, smoking, black race, obesity, low fibre diet, insulin resistance, and the metabolic syndrome. We have searched Medline for the metabolic syndrome and its relation to CRC, and metformin as a potential treatment of colorectal cancer. Administration of metformin alone or in combination with chemotherapy has been shown to suppress CRC. The mechanism that explains how insulin resistance is associated with CRC is complex and not fully understood. In this review we have summarised studies which showed an association with the metabolic syndrome as well as studies which tackled metformin as a potential treatment of CRC. In addition, we have also provided a summary of how metformin at the cellular level can induce changes that suppress the activity of cancer cells.

Weight Change and Obesity Are Associated with a Risk of Adenoma Recurrence

BACKGROUND

Obesity is reportedly a risk factor for colorectal adenoma. However, the influence of weight change and obesity on colorectal adenoma recurrence is unclear.

AIM

To investigate whether weight change and obesity are associated with recurrence and development of colorectal adenoma.

PATIENTS AND METHODS

Of 62,171 asymptomatic subjects who underwent a colonoscopy for a heath checkup between 2010 and 2011, this longitudinal study was performed with the 5297 subjects who underwent another colonoscopy between 2012 and 2013. The risk of recurrence or development of adenoma according to quartiles of weight change (<-1.6, -1.6 to 0.1, 0.2-1.8, and ≥1.9 kg) and baseline BMI categories (<25, 25-29, and ≥30 kg/m(2)) was assessed using Cox proportional hazards modeling.

RESULTS

The average period between visits 1 and 2 was 2.2 ± 0.6 years. Among the 2176 subjects with adenomas, the risk of recurrence of any adenoma increased with increasing weight change quartiles (p for trend = 0.030), whereas the risk of recurrence of advanced adenoma was not associated with weight change (p for trend = 0.852). The risk of recurrence of advanced adenoma increased with increasing baseline BMI categories (p for trend = 0.029). Among 3121 subjects with no adenoma, the risk of developing any adenoma increased with increasing baseline BMI categories (p for trend <0.001). However, the risk of developing any or advanced adenoma was not associated with weight change.

CONCLUSIONS

Weight change over 2.2 years affected adenoma recurrence and obesity was related to advanced adenoma recurrence and adenoma development.

Metformin, Diabetes, and Survival among U.S. Veterans with Colorectal Cancer

BACKGROUND

Metformin has been associated with improved colorectal cancer survival, but investigations are limited by small numbers of patients and confounding by diabetic severity. We examined the association between metformin use and overall survival (OS) in patients with diabetes and colorectal cancer in a large population of U.S. veterans, while adjusting for measures of diabetic severity.

METHODS

Patients diagnosed with colorectal cancer from January 2001 to December 2008 were identified from the Veterans Affairs Central Cancer Registry. Multivariable models were used to examine the adjusted association of OS with diabetes and use of antidiabetic medications.

RESULTS

There were 21,352 patients diagnosed with colorectal cancer identified (n = 16,355 nondiabetic patients, n = 2,038 diabetic patients on metformin, n = 2,136 diabetic patients on medications other than metformin, n = 823 diabetic patients not on antidiabetic medication). Diabetic patients had a significantly worse OS than nondiabetic patients, but metformin users had only a 10% increase in death (HR_adj 1.10; 95% CI, 1.03-1.17, P = 0.004), as compared with 22% for users of other antidiabetic medications (HR_adj 1.22; 95% CI, 1.15-1.29, P < 0.0001). Among colorectal cancer patients with diabetes, metformin users had a 13% improved OS versus patients taking other antidiabetic medications (HR_adj 0.87; 95% CI, 0.79-0.95, P = 0.003), while diabetic patients not on any antidiabetic medications did not differ with respect to OS (HR_adj 1.02; 95% CI, 0.90-1.15, P = 0.76).

CONCLUSIONS

Among diabetics with colorectal cancer, metformin use is associated with improved survival, despite adjustments for diabetes severity and other risk factors.

IMPACT

These data lend further support to the conduct of randomized studies of possible anticancer effects of metformin among patients with colorectal cancer. Cancer Epidemiol Biomarkers Prev; 25(10); 1418-25. ©2016 AACR.

Associations between amount of smoking and alcohol intake and risk of colorectal neoplasm

BACKGROUND AND AIM

Although smoking and alcohol has been linked to an increased risk of colorectal neoplasm (CRN), large-scale studies to identify dose-dependent relationship between amount of smoking and alcohol consumption and risk of CRN are rare. We aimed to investigate the risk for CRN according to the amount of smoking and alcohol intake in a large sample of Korean adults.

METHODS

A cross-sectional study was performed on 31,714 examinees aged ≥30 years undergoing their first colonoscopy as part of routine preventive health care between 2010 and 2011. Never smokers were compared with six groups of smokers according to smoking amount, and individuals with alcohol intake of ≤ 6.25 g ethanol per day were compared with three groups according to alcohol amount.

RESULTS

In adjusted models, the risk of overall CRN increased with increasing amount of smoking (P for trend < 0.001). The adjusted odds ratios for overall CRN comparing never smokers with six smoker groups according to smoking amount (≤2.50, 2.51-5.60, 5.61-9.00, 9.01-13.00, 13.01-19.50, and ≥19.51 pack-years) were 1.02, 1.19, 1.35, 1.53, 1.63, and 2.03, respectively. In addition, the risk of both non-advanced and advanced CRN increased with increasing amount of smoking (both P for trend < 0.001). However, the amount of alcohol consumption was not correlated with the risk of CRN.

CONCLUSIONS

The prevalence of CRN was associated with increasing amount of smoking in a dose-response manner, whereas it was not associated with the amount of alcohol consumption. Our study suggests that smoking amount as well as smoking status should be considered for CRN risk stratification.

Inhibitory effect of metformin therapy on the incidence of colorectal advanced adenomas in patients with diabetes

BACKGROUND/AIMS

Metformin use has been associated with decreased colorectal cancer risk and mortality among diabetic patients. Recent research suggests that metformin use may decrease the incidence of colorectal adenomas in diabetic patients with previous colorectal cancer. This study aimed to assess the clinical effect of metformin use on the development of colorectal adenomas in diabetic patients without previous colorectal cancer.

METHODS

Among 604 consecutive diabetic patients who underwent colonoscopic surveillance after initial colonoscopy between January 2002 and June 2012, 240 patients without previous colorectal cancer were enrolled in this study and were divided in two groups: 151 patients receiving metformin and 89 patients not receiving metformin. Patient demographics and clinical characteristics as well as the colorectal adenoma incidence rate were retrospectively analyzed.

RESULTS

The incidence rate of total colorectal adenomas was not different according to metformin use (P=0.349). However, the advanced adenoma incidence rate was significantly lower in the metformin group compared with the non-metformin group (relative risk [RR], 0.09; P=0.011). Metformin use was independently associated with a decreased incidence of advanced colorectal adenomas after adjustment for clinically relevant factors (RR, 0.072; P=0.016). In addition, the cumulative development rate of advanced adenomas during follow-up was significantly lower in the metformin group compared with the non-metformin group (P=0.007).

CONCLUSIONS

Metformin use in diabetic patients without previous colorectal cancer is associated with a lower risk of advanced colorectal adenomas.