Association of diabetes duration and diabetes treatment with the risk of hepatocellular carcinoma

Metformin and reduced risk of hepatocellular carcinoma in diabetic patients: a meta-analysis

OBJECTIVES

Recent epidemiological studies suggest that metformin treatment may reduce the risks of cancer and overall cancer mortality among patients with diabetes mellitus (DM). However, data on hepatocellular carcinoma (HCC) are very limited and inconsistent. This meta-analysis was designed to pool data currently available to determine the association between metformin use and HCC among diabetic patients.

METHODS

The Medline and Embase databases were searched to identify the relevant studies between January 1966 and December 2011. The overall analysis was derived using a random-effects meta-analysis model (DerSimonian and Laird method). Subgroup analysis was performed to explore the source of heterogeneity and validate the results from overall analysis. The Newcastle-Ottawa Quality assessment scales were adopted for quality assessment; Begg's funnel plot and Egger's regression asymmetry test were used to detect the publication bias.

RESULTS

A total of seven studies were identified, including three cohort studies and four case-control studies. Based on the available data, the overall prevalence of HCC was 3.40% (562/16,549) in DM patients. The overall analysis showed a significantly reduced risk of HCC in metformin users versus nonusers in diabetic patients (relative risk (RR) 0.24, 95% confidence interval (CI) 0.13-0.46, p < 0.001). Fifteen subgroup analyses were performed, and most of them (12/15 = 80%) provided supporting evidence for the results of overall analysis. Begg's (Z = -0.15, p = 0.8819) and Egger's test (t = -0.79, p = 0.468) showed no significant risk of having a publication bias.

CONCLUSION

Metformin treatment was associated with reduced risk of HCC in diabetic patients. To clarify this relationship, more high-quality studies are required.

The effect of sorafenib treatment on the diabetic status of patients with renal cell or hepatocellular carcinoma

AIM

To evaluate the effect of sorafenib on the glucose tolerance and diabetic status of patients with metastatic renal cell carcinoma (RCC) or advanced hepatocellular carcinoma (HCC).

MATERIALS & METHODS

Eighty patients with metastatic RCC or advanced HCC received 400 mg sorafenib twice daily for an average of approximately 8 and 5 months, respectively; 22 had diabetes mellitus and three had prediabetes.

RESULTS

One of 55 nondiabetic patients, and one of three patients with impaired fasting glucose or impaired glucose tolerance developed diabetes mellitus, one of 12 patients on oral antihyperglycemic agents switched to insulin and no patient treated with insulin needed to increase their dose.

CONCLUSION

Sorafenib has the potential to be a feasible and safe treatment option for patients with advanced HCC or metastatic RCC and comorbid diabetes mellitus or prediabetes.

Metformin and the risk of cancer: time-related biases in observational studies

OBJECTIVE

Time-related biases in observational studies of drug effects have been described extensively in different therapeutic areas but less so in diabetes. Immortal time bias, time-window bias, and time-lag bias all tend to greatly exaggerate the benefits observed with a drug.

RESEARCH DESIGN AND METHODS

These time-related biases are described and shown to be prominent in observational studies that have associated metformin with impressive reductions in the incidence of and mortality from cancer. As a consequence, metformin received much attention as a potential anticancer agent; these observational studies sparked the conduction of randomized, controlled trials of metformin as cancer treatment. However, the spectacular effects reported in these studies are compatible with time-related biases.

RESULTS

We found that 13 observational studies suffered from immortal time bias; 9 studies had not considered time-window bias, whereas other studies did not consider inherent time-lagging issues when comparing the first-line treatment metformin with second- or third-line treatments. These studies, subject to time-related biases that are avoidable with proper study design and data analysis, led to illusory extraordinarily significant effects, with reductions in cancer risk with metformin ranging from 20 to 94%. Three studies that avoided these biases reported no effect of metformin use on cancer incidence.

CONCLUSIONS

Although observational studies are important to better understand the effects of drugs, their proper design and analysis is essential to avoid major time-related biases. With respect to metformin, the scientific evidence of its potential beneficial effects on cancer would need to be reassessed critically before embarking on further long and expensive trials.

Evaluation of a novel non-invasive (13) C-glucose breath test for the identification of diabetes mellitus in cirrhotic patients

AIM

  Diabetes mellitus (DM) has been reported to worsen the long-term prognosis of cirrhotic patients, and many studies have reported that DM is an independent risk factor for hepatocellular carcinoma. However, an accurate diagnosis of DM is sometimes difficult in cirrhotic patients. Recently, a novel non-invasive (13) C-glucose breath test has been reported to be useful for diagnosing insulin resistance in non-cirrhotic patients. The aim of this study was to evaluate the efficacy of this tool for the identification of DM in cirrhotic patients.

METHODS

  Thirty eight cirrhotic patients with normal fasting serum glucose and hemoglobin A1c levels underwent the (13) C-glucose breath test and the oral glucose tolerance test. Blood and breath samples were collected at baseline and at 30, 60 and 120 min after ingestion of 100 mg (13) C-labeled glucose and 75 g glucose.

RESULTS

  There was a strong correlation between the change in the concentrations at 2 h for the measured (13) C-glucose breath test (2h-BT) and the 2 h plasma glucose level (r = -0.60, P < 0.0001). In a receiver-operator curve analysis using the 2h-BT, the area under the curve was determined to be 0.88, with a sensitivity and specificity (cut-off value of 3.5‰) of 82% and 85%, respectively, for the detection of DM. Multivariate analysis showed the 2h-BT to be an independent parameter to identify DM.

CONCLUSION

  The (13) C-glucose breath test is a useful tool and has the potential to become a routine outpatient examination for the screening of DM in cirrhotic patients.

Insulin therapy and cancer in type 2 diabetes

Despite the availability of many other agents, insulin is widely used as a treatment for type 2 diabetes. In vitro, insulin stimulates the growth of cancer cells, through the interaction with insulin-like growth factor-1 (IGF-1) receptors and its own receptors. In observational surveys on type 2 diabetes, insulin therapy is associated with an increased incidence of several forms of cancer, although it is difficult to discriminate the effect of confounders from that of insulin itself. Randomized trials do not confirm the increased risk associated with insulin therapy, although they do not allow to rule out some negative effects on specific forms of cancer, at least at higher doses. Among insulin analogues, glargine has a higher affinity for the IGF-1 receptor and a greater mitogenic potency in vitro than human insulin, but it is extensively metabolized in vitro to products with low IGF-1 receptor affinity. Overall, epidemiological studies suggest a possible increase of risk with glargine, with respect to human insulin, only at high doses and for some forms of cancer (i.e., breast). Data from clinical trials do not confirm, but are still insufficient to totally exclude, such increased risk. However, beneficial effects of insulin outweigh potential cancer risks.

Thiazolidinedione use and cancer incidence in type 2 diabetes: a systematic review and meta-analysis

AIMS

Evidence suggests thiazolidinediones (TZDs) may modify the relationship between type 2 diabetes and cancer incidence. We aimed to summarize data from randomized controlled trials (RCTs) and observational studies to examine risk of overall and site-specific cancers with TZD use in individuals with type 2 diabetes.

METHODS

We searched 12 key biomedical databases and seven grey literature sources up to June 2011, without language restrictions. We performed separate meta-analyses according to cancer site and study design, comparing ever-use to never-use of TZDs, and pioglitazone alone.

RESULTS

The search yielded 1338 unique citations; we included four RCT, seven cohort and nine nested case-control studies, contributing data from 2.5 million people. Estimates from observational studies suggested any TZD use was associated with a decreased risk of colorectal (pooled RR: 0.93, 95%CI 0.87-1.00, P=0.04, I(2)=30%), lung (pooled RR: 0.91, 95%CI 0.84-0.98, P=0.02, heterogeneity (I(2))=35%) and breast (pooled RR: 0.89, 95%CI 0.81-0.98, P=0.02, I(2)=44%) cancer. Risk of overall cancer with TZD use was not significantly modified in RCTs (pooled RR: 0.92, 95%CI 0.79-1.07, P=0.26, I(2)=0%) or observational studies (pooled OR: 0.95, 95%CI 0.78-1.16, P=0.63, I(2)=70%). Pioglitazone use was, however, associated with a decreased risk of overall cancer (colorectal, lung, breast, prostate and renal sub-sites combined) in observational studies (pooled RR: 0.95, 95%CI 0.91-0.99, P=0.009, I(2)=0%).

CONCLUSIONS

Our findings suggest that use of TZDs is associated with a modest but significantly decreased risk of lung, colorectal and breast cancers. Results were limited by the paucity of studies designed to answer our research question. Further evaluation of TZD use, cancer risk factors and potential confounders is required.

Enhanced cytotoxic effect of low doses of metformin combined with ionizing radiation on hepatoma cells via ATP deprivation and inhibition of DNA repair

Metformin, one of the most widely used antidiabetic drugs, has recently been associated with potential antitumorigenic effects. In this study, we evaluated the possible cytotoxic impact of combined low doses of metformin and ionizing radiation (IR) on 2 human hepatoma cell lines. The cytotoxic effect of metformin combined with IR was subsequently determined by clonogenic survival and cell cycle assays, assessment of mitochondrial complex I and lactate dehydrogenase (LDH) activity, measurement of cellular adenosine triphosphate (ATP) levels, comet assay and analyses of the formation and disappearance of phosphorylated histone H2AX (γ-H2AX) protein. The combination of metformin and IR caused a much stronger cytotoxicity than the treatment with metformin or IR alone, leading to an ~80% decrease in cell viability and ~35% increase in the accumulation of cells in the G2/M phase of the cell cycle in the 2 hepatoma cell lines. In addition, a reduction in mitochondrial complex I activity (~70%) and a significant increase in LDH activity, as well as lactate production were observed in the cells exposed to metformin. Interestingly, a severe depletion in ATP, increased olive tail moment and the delayed disappearance of γ-H2AX expression were detected in the hepatoma cells treated by metformin plus IR. These findings show that the combination of a low concentration of metformin and IR results in the considerable enhancement of cytotoxic effects in human hepatoma cell lines, leading to decreased DNA repair by reducing ATP production. The data provided in this study may elucidate the remarkable efficiency of this combination treatment and suggest that metformin may be used as a potential adjunct to the radiotherapy of hepatocellular carcinoma.

Epidemiology and surveillance of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most frequently occurring malignancies and has a high mortality rate. The incidence of HCC differs greatly according to the geographic area. East and Southeast Asia, as well as middle and West Africas have the highest prevalence of HCC. The risk factors for developing HCC are well known and include cirrhosis, hepatitis B virus (HBV) infection, hepatitis C virus (HCV) infection, alcohol consumption, smoking, diabetes, and nonalcoholic steatohepatitis. Cirrhosis is the most significant risk factor, and there is a correlation between the degree of noninvasively measured liver fibrosis and the risk of HCC occurrence. HBV exerts carcinogenic effects by several mechanisms, including host genome integration, and studies have revealed that HBV replication predicts HCC development. HCV induces multistep carcinogenesis from inflammation, to fibrosis and liver cancer. HCC is an appropriate target for surveillance programs for early cancer detection. Currently, liver ultrasonography (US) combined with serum alpha-fetoprotein (AFP, a biomarker of HCC) measurement every 6 months is the standard method of HCC surveillance. Although US is the most widely used tool, its sensitivity in detecting early HCC (i.e., within the Milan criteria) during surveillance is only 63%. AFP is the representative biomarker for both HCC surveillance and diagnosis; however, the unsatisfactory performance of AFP as a surveillance tool means that a novel biomarker or combination with other serum markers is required. Des-gamma-carboxy prothrombin and AFP-L3 are candidate biomarkers that are complementary to AFP. The strategies of HCC surveillance vary in different countries according to the healthcare system, the resources available, and health insurance coverage. Many studies have shown that the rate of early cancer detection and rate of application of curative therapies were increased, as was the survival time, by HCC surveillance, which should now become a part of standard care, rather than just a recommendation. Improved US technology and the discovery of new biomarkers are necessary to make further progress in HCC surveillance.

Metformin in cancer: translational challenges

The anti-diabetic drug metformin is rapidly emerging as a potential anti-cancer agent. Metformin, effective in treating type 2 diabetes and the insulin resistance syndromes, improves insulin resistance by reducing hepatic gluconeogenesis and by enhancing glucose uptake by skeletal muscle. Epidemiological studies have consistently associated metformin use with decreased cancer incidence and cancer-related mortality. Furthermore, numerous preclinical and clinical studies have demonstrated anti-cancer effects of metformin, leading to an explosion of interest in evaluating this agent in human cancer. The effects of metformin on circulating insulin levels indicate a potential efficacy towards cancers associated with hyperinsulinaemia; however, metformin may also directly inhibit tumour growth. In this review, we describe the mechanism of action of metformin and summarise the epidemiological, clinical and preclinical evidence supporting a role for metformin in the treatment of cancer. In addition, the challenges associated with translating preclinical results into therapeutic benefit in the clinical setting will be discussed.

Hepatocellular carcinoma in non-alcoholic fatty liver disease: an emerging menace

Hepatocellular carcinoma (HCC) is a common cancer worldwide that primarily develops in cirrhosis resulting from chronic infection by hepatitis B virus and hepatitis C virus, alcoholic injury, and to a lesser extent from genetically determined disorders such as hemochromatosis. HCC has recently been linked to non-alcoholic fatty liver disease (NAFLD), the hepatic manifestation of obesity and related metabolic disorders such as diabetes. This association is alarming due to the globally high prevalence of these conditions and may contribute to the rising incidence of HCC witnessed in many industrialized countries. There is also evidence that NAFLD acts synergistically with other risk factors of HCC such as chronic hepatitis C and alcoholic liver injury. Moreover, HCC may complicate non-cirrhotic NAFLD with mild or absent fibrosis, greatly expanding the population potentially at higher risk. Major systemic and liver-specific molecular mechanisms involved include insulin resistance and hyperinsulinemia, increased TNF signaling pathways, and alterations in cellular lipid metabolism. These provide new targets for prevention, early recognition, and effective treatment of HCC associated with NAFLD. Indeed, both metformin and PPAR gamma agonists have been associated with lower risk and improved prognosis of HCC. This review summarizes current evidence as it pertains to the epidemiology, pathogenesis, and prevention of NAFLD-associated HCC.

Cancer risk associated with use of metformin and sulfonylurea in type 2 diabetes: a meta-analysis

OBJECTIVE

Oral antidiabetic drugs (including metformin and sulfonylurea) may play a role in the relationship between type 2 diabetes and cancer. To quantify the association between metformin and sulfonylurea and the risk of cancer, we performed a meta-analysis of available studies on the issue.

MATERIALS AND METHODS

We performed a MEDLINE search for observational studies that investigated the risk of all cancers and specific cancer sites in relation to use of metformin and/or sulfonylurea among patients with type 2 diabetes mellitus. Fixed- and random-effect models were fitted to estimate the summary relative risk (RR). Between-study heterogeneity was tested using χ(2) statistics and measured with the I(2) statistic. Publication bias was evaluated using funnel plot and Egger's regression asymmetry test.

RESULTS

Seventeen studies satisfying inclusion criteria and including 37,632 cancers were evaluated after reviewing 401 citations. Use of metformin was associated with significantly decreased RR of all cancers (summary RR 0.61, 95% confidence interval [CI] 0.54-0.70), colorectal cancer (0.64, 95% CI 0.54-0.76), and pancreatic cancer (0.38, 95% CI 0.14-0.91). With the exception of colorectal cancer, significant between-study heterogeneity was observed. Evidence of publication bias for metformin-cancer association was also observed. There was no evidence that metformin affects the risk of breast and prostate cancers, nor that sulfonylurea affects the risk of cancer at any site.

CONCLUSIONS

Metformin, but not sulfonylurea, appears to reduce subsequent cancer risk. This has relevant implications in light of the exploding global epidemic of diabetes.

Diabetes mellitus as a risk factor for gastrointestinal cancers among postmenopausal women

OBJECTIVES

While diabetes has been linked to several cancers in the gastrointestinal (GI) tract, findings have been mixed for sites other than colorectal and liver cancer. We used the Women's Health Initiative (WHI) data and conducted a comprehensive assessment of associations between diabetes and GI malignancy (esophagus, stomach, liver, biliary, pancreas, colon, and rectal).

METHODS

A total of 145,765 postmenopausal women aged 50-79 enrolled in the WHI were followed for a mean 10.3 years. Cox proportional hazard regression models were used to estimate hazard ratios (HRs) and 95 % confidence intervals (CIs) for the association between GI cancers and diagnosed diabetes, including its duration and treatment.

RESULTS

Diabetes at enrollment was associated with increased risk of liver (HR = 2.97; 95 % CI, 1.66-5.32), pancreatic (HR = 1.62; 95 % CI, 1.15-2.30), colon (HR = 1.38; 95 % CI, 1.14-1.66), and rectal (HR = 1.87, 95 % CI: 1.22-2.85) cancer. Diabetes severity, assessed by duration or need for pharmacotherapy, appeared to have stronger links to risk of liver, pancreatic, and rectal cancer, but not colon cancer. There was no statistically significant association of diabetes with biliary, esophageal, and stomach cancers.

CONCLUSION

Type 2 diabetes is associated with a significantly increased risk of cancers of the liver, pancreas, colon, and rectum in postmenopausal women. The suggestion that diabetes severity further increases these cancer risks requires future studies.

Diabetes mellitus is associated with increased mortality in patients receiving curative therapy for hepatocellular carcinoma

BACKGROUND

Diabetes mellitus (DM) is closely associated with hepatocarcinogenesis. This study explores the prognostic impact of DM in patients who received curative therapy for localized hepatocellular carcinoma (HCC).

METHODS

Patients who had been diagnosed with stage I or II HCC in 2003 and 2004 and received surgical resection or local ablation therapy were identified from the population-based Taiwan National Cancer Registry. Data pertaining to DM and other comorbidities were retrieved from the Taiwan National Health Insurance database. Liver cancer-specific survival (LCS), liver disease-related survival (LDS) and overall survival (OS) rates were compared between patients with and without DM. The presence of other comorbidities and tumor status were adjusted using multivariate analysis.

RESULTS

A total of 931 patients who fulfilled the study criteria were analyzed; 185 (20%) of them had DM (type 1 or type 2). The LCS, LDS, and OS rates were significantly worse for patients with DM than patients without DM (all p < .001). After adjusting for age, sex, tumor stage, treatment, and the presence of other comorbidities, DM remained an independent predictor of poorer LCS (hazard ratio [HR] = 1.57; p < .001), LDS (HR = 1.70; p < .001), and OS (HR = 1.69; p < .001). The associations between DM and mortality were consistent among subgroups, irrespective of tumor size, stage, treatment modality, and liver cirrhosis.

CONCLUSIONS

DM is an independent factor for poorer prognosis in patients who received curative therapy for localized HCC.

Diabetes and cancer I: risk, survival, and implications for screening

Type 2 diabetes mellitus (DM) and cancer are common diseases that are frequently diagnosed in the same individual. An association between the two conditions has long been postulated. Here, we review the epidemiological evidence for increased risk of cancer, decreased cancer survival, and decreased rates of cancer screening in diabetic patients. The risk for several cancers, including cancers of the pancreas, liver, colorectum, breast, urinary tract, and endometrium, is increased in patients with DM. In a pooled risk analysis weighting published meta-analytic relative risk (RR) for individual cancer by differences in their incidence rates, we found a population RR of 0.97 (95 % CI, 0.75-1.25) in men and 1.29 (95 % CI, 1.16-1.44) in women. All meta-analyses showed an increased relative risk for cancer in diabetic men, except studies of prostate cancer, in which a protective effect was observed. The relationship between diabetes and cancer appears to be complex, and at present, a clear temporal relationship between the two conditions cannot be defined. DM also impacts negatively on cancer-related survival outcomes and cancer screening rates. The overwhelming evidence for lower cancer screening rates, increased incidence of certain cancers, and poorer prognosis after cancer diagnosis in diabetic patients dictates a need for improved cancer care in diabetic individuals through improved screening measures, development of risk assessment tools, and consideration of cancer prevention strategies in diabetic patients. Part two of this review focuses on the biological and pharmacological mechanisms that may account for the association between DM and cancer.

Systematic review and meta-analysis of insulin therapy and risk of cancer

Recent epidemiological studies suggest that treatment with insulin may promote cancer growth. The present systematic review and meta-analysis of published observational studies was conducted to assess the risk of cancer during treatment with insulin. A search of online database through January 2011 was performed and examined the reference lists of pertinent articles, limited to observational studies in humans. Pooled relative risks (RRs) and 95% confidence intervals (CIs) were calculated with a random-effects model. Fifteen studies (five case-control and ten cohort studies) were included, with 562,043 participants and 14,085 cases of cancer. Insulin treatment was associated with an increased risk of overall cancer [summary RR (95% CI)=1.39 (1.14, 1.70)]. Summary RR (9% CI) for case-control studies was 1.83 (0.99, 3.38), whereas RR for cohort studies was 1.28 (1.03, 1.59). These results were consistent between studies conducted in the USA and in Europe. For studies that included combined type 1 and 2 diabetes, the summary estimate was stronger than studies including only type 2 diabetes mellitus. The association between insulin treatment and cancer was stronger for pancreatic cancer [summary RR (95% CI)=4.78 (3.12, 7.32)] than for colorectal cancer [1.50 (1.08, 2.08)]. Insulin treatment was not associated with breast, prostate, and hepatocelluar cancer, and their effect estimates were not statistically significant. Our findings support an association between insulin use and increased risk of overall, pancreatic, and colorectal cancer.

Survival advantage observed with the use of metformin in patients with type II diabetes and colorectal cancer

BACKGROUND

Patients with type II diabetes mellitus (DM) have an increased risk of adenomatous colorectal (CRC) polyps and CRC cancer. The use of the anti-hyperglycemic agent metformin is associated with a reduced incidence of cancer-related deaths.

METHODS

We retrospectively evaluated the medical records of 4758 patients seen at a single institution and determined that 424 patients were identified by their physicians as having type II DM and CRC cancer. Data were subsequently acquired determining the subject's age, body mass index (BMI), and disease date of diagnosis, stage, site of cancer, treatment, and survival.

RESULTS

Patients with type II DM and CRC cancer treated with metformin as one of their diabetic medications had a survival of 76.9 months (95% CI=61.4-102.4) as compared with 56.9 months in those patients not treated with metformin (95% CI=44.8-68.8), P=0.048. By using a multivariable Cox regression model adjusted for age, sex, race, BMI, and initial stage of disease, we demonstrated that type II diabetic patients treated with metformin had a 30% improvement in overall survival (OS) when compared with diabetic patients treated with other diabetic agents.

CONCLUSION

Colorectal cancer patients with DM treated with metformin as part of their diabetic therapy appear to have a superior OS.

Insulin resistance is associated with a higher risk of hepatocellular carcinoma in cirrhotic HIV/HCV-co-infected patients: results from ANRS CO13 HEPAVIH

BACKGROUND & AIMS

Compared to HCV-mono-infected patients, hepatocellular carcinoma (HCC) occurs at younger age in HIV/HCV-co-infected patients, is markedly more advanced at diagnosis, is less amenable to curative treatment, and has a more severe outcome. The aim of this study was to identify factors predictive of HCC occurrence in a large cohort of HIV/HCV-co-infected patients with cirrhosis.

METHODS

This study involved 244 HIV/HCV-co-infected patients included in the ANRS CO13 HEPAVIH cohort, who had HCV-related cirrhosis (clinically or histologically proven cirrhosis, or liver stiffness ≥12.5 kPa) and no signs of HCC at baseline. Cox proportional hazards models were used to identify factors associated with HCC occurrence.

RESULTS

During a median follow-up of 2.6 (IQR, 1.8-3.5) years, 21 patients (8.6%) developed HCC. Diagnosis of HCC was based on histology in 5 patients (24%) and non-invasive criteria in 16 patients (76%). In univariate analyses, the following factors were related to HCC occurrence: age, previous cirrhosis decompensation, a HOMA value >3.8 (patients with treated diabetes were excluded from the HOMA calculation), a lower platelet count, a lower prothrombin level, and higher alpha-fetoprotein levels. The HOMA value was >3.8 at baseline in 66.7% of patients who developed HCC and in 35.3% of the remaining patients (p=0.016). In multivariate analysis, age over 50 years (adjusted RR 3.2, 95% CI 1.2-9.0; p=0.02) and a HOMA value >3.8 (adjusted RR 3.4, 95% CI 1.1-10.3; p=0.03) remained significantly associated with HCC occurrence.

CONCLUSIONS

As in HCV-mono-infected patients with HCV-related cirrhosis, insulin resistance appears to play a key role in HCC occurrence in HCV/HIV-co-infected patients with cirrhosis. This finding calls for specific screening strategies for patients with a particularly high risk of developing HCC.

Metformin use is associated with better survival of diabetic patients with pancreatic cancer

PURPOSE

Accumulating evidence suggests that metformin has antitumor activity. The aim of this study was to determine whether metformin use has a survival benefit in patients with pancreatic cancer.

EXPERIMENTAL DESIGN

We conducted a retrospective study of patients with diabetes and pancreatic cancer treated at The University of Texas MD Anderson Cancer Center (Houston, TX). Information on diabetes history, including treatment modalities and clinical outcome of pancreatic cancer, was collected using personal interviews and medical record review. Survival analysis was carried out using a Kaplan-Meier plot, log-rank test, and Cox proportional hazards regression models.

RESULTS

Among the 302 patients identified, there were no significant differences in demographic or major clinical characteristics between the patients who had received metformin (n = 117) and those who had not (n = 185). The 2-year survival rate was 30.1% for the metformin group and 15.4% for the non-metformin group (P = 0.004; χ(2) test). The median overall survival time was 15.2 months for the metformin group, and 11.1 months for the non-metformin group (P = 0.004, log-rank test). Metformin users had a 32% lower risk of death; the HR (95% confidence interval) was 0.68 (0.52-0.89) in a univariate model (P = 0.004), 0.64 (0.48-0.86) after adjusting for other clinical predictors (P = 0.003), and 0.62 (0.44-0.87) after excluding insulin users (P = 0.006). Metformin use was significantly associated with longer survival in patients with nonmetastatic disease only.

CONCLUSIONS

Our finding that metformin use was associated with improved outcome of patients with diabetes and pancreatic cancer should be confirmed in independent studies. Future research should prospectively evaluate metformin as a supplemental therapy in this population.

Cancer risk in diabetic patients treated with metformin: a systematic review and meta-analysis

BACKGROUND

A growing body of evidence has suggested that metformin potentially reduces the risk of cancer. Our objective was to enhance the precision of estimates of the effect of metformin on the risk of any-site and site-specific cancers in patients with diabetes.

METHODS/PRINCIPAL FINDINGS

We performed a search of MEDLINE, EMBASE, ISI Web of Science, Cochrane Library, and ClinicalTrials.gov for pertinent articles published as of October 12, 2011, and included them in a systematic review and meta-analysis. We calculated pooled risk ratios (RRs) for overall cancer mortality and cancer incidence. Of the 21,195 diabetic patients reported in 6 studies (4 cohort studies, 2 RCTs), 991 (4.5%) cases of death from cancer were reported. A total of 11,117 (5.3%) cases of incident cancer at any site were reported among 210,892 patients in 10 studies (2 RCTs, 6 cohort studies, 2 case-control studies). The risks of cancer among metformin users were significantly lower than those among non-metformin users: the pooled RRs (95% confidence interval) were 0.66 (0.49-0.88) for cancer mortality, 0.67 (0.53-0.85) for all-cancer incidence, 0.68 (0.53-0.88) for colorectal cancer (n = 6), 0.20 (0.07-0.59) for hepatocellular cancer (n = 4), 0.67 (0.45-0.99) for lung cancer (n = 3).

CONCLUSION/SIGNIFICANCE

The use of metformin in diabetic patients was associated with significantly lower risks of cancer mortality and incidence. However, this analysis is mainly based on observational studies and our findings underscore the more need for long-term RCTs to confirm this potential benefit for individuals with diabetes.

Diabetes mellitus and risk of hepatocellular carcinoma: a systematic review and meta-analysis

Studies of diabetes and hepatocellular carcinoma (HCC) yielded inconsistent findings. This meta-analysis was conducted to examine the association between diabetes and risk of HCC. Studies were identified by searching PUBMED and MEDLINE database up to February 2011. Pooled risk estimates were calculated using the random-effects model. Potential sources of heterogeneity were explored by subgroup analyses. A total of 17 case-control studies and 32 cohort studies were included in the meta-analysis. The combined risk estimate of all studies showed a statistically significant increased risk of HCC prevalence among diabetic individuals (RR = 2.31, 95% CI: 1.87-2.84). The pooled risk estimate of 17 case-control studies (OR = 2.40, 95% CI: 1.85-3.11) was slightly higher than that from 25 cohort studies (RR = 2.23, 95% CI: 1.68-2.96). Metformin treatment was potentially protective. On the contrary, long duration of diabetes and sulfonylureas or insulin treatment possibly increase HCC risk. Also meta-analysis of 7 cohort studies found a statistically significant increased risk of HCC mortality (RR = 2.43, 95% CI: 1.66-3.55) for individuals with (versus without) diabetes. This meta-analysis shows that diabetes is associated with moderately increased risk of HCC prevalence, as well as HCC mortality. Considering the rapidly increasing prevalence of diabetes mellitus, the study underlines the need for cancer prevention in diabetic individuals. Further investigation is needed to focus on the potential mechanism for the pathogenesis of HCC and the link between HCC and different types, severity, treatment and duration of diabetes.

Risk of hepatocellular carcinoma in diabetic patients and risk reduction associated with anti-diabetic therapy: a population-based cohort study

OBJECTIVES

Using population-based representative insurance claims data, the risk of developing hepatocellular carcinoma (HCC) among diabetes mellitus (DM) patients, as well as whether DM medications alter the risk of developing HCC were investigated.

METHODS

From the Taiwan National Health Insurance Research Database, 19,349 newly diagnosed DM patients 20 years and older and 77,396 comparison subjects without DM were identified from claims from 2000 to 2005. The incidences of HCC at the end of 2008 and the risks associated with hepatitis B and hepatitis C were determined. Whether metformin and thiazolidinediones reduce the risk of developing HCC was also measured.

RESULTS

The incidence of HCC was twice higher in the DM group compared with the non-DM group (21.0 vs. 10.4 per 10,000 person-years), with an adjusted hazard ratio (HR) of 1.73 (95% confidence interval (CI)=1.47-2.03) using multivariable Cox proportional hazard regression. Male sex, cirrhosis, hepatitis B, and hepatitis C were significant independent factors that predict HCC, with HRs of 2.32, 8.65, 2.52, and 5.61, respectively. In the stratified analysis, the HR increased to 72.4 (95% CI=42.9-122) among patients with DM, cirrhosis, and hepatitis C. HCC risk reduction was greater for diabetics taking metformin than those taking thiazolidinediones (51 vs. 44% reduction).

CONCLUSIONS

Comorbidity with cirrhosis and/or hepatitis appears to be associated with an extremely increased risk of developing HCC among DM patients. These high-risk patients should be closely monitored for HCC. The use of metformin or thiazolidinediones may reduce the risk of developing HCC.

Lower risk of cancer in patients on metformin in comparison with those on sulfonylurea derivatives: results from a large population-based follow-up study

OBJECTIVE

Numerous studies have suggested a decreased risk of cancer in patients with diabetes on metformin. Because different comparison groups were used, the effect magnitude is difficult to estimate. Therefore, the objective of this study was to further analyze whether, and to what extent, use of metformin is associated with a decreased risk of cancer in a cohort of incident users of metformin compared with users of sulfonylurea derivatives.

RESEARCH DESIGN AND METHODS

Data for this study were obtained from dispensing records from community pharmacies individually linked to hospital discharge records from 2.5 million individuals in the Netherlands. The association between the risk of cancer in those using metformin compared with those using sulfonylurea derivatives was analyzed using Cox proportional hazard models with cumulative duration of drug use as a time-varying determinant.

RESULTS

Use of metformin was associated with a lower risk of cancer in general (hazard ratio 0.90 [95% CI 0.88-0.91]) compared with use of sulfonylurea derivatives. When specific cancers were used as end points, similar estimates were found. Dosage-response relations were identified for users of metformin but not for users of sulfonylurea derivatives.

CONCLUSIONS

In our study, cumulative exposure to metformin was associated with a lower risk of specific cancers and cancer in general, compared with cumulative exposure to sulfonylurea derivatives. However, whether this should indeed be seen as a decreased risk of cancer for the use of metformin or as an increased risk of cancer for the use sulfonylurea derivatives remains to be elucidated.

Hepatocellular carcinoma in non-alcoholic steatohepatitis: Growing evidence of an epidemic?

The incidence of hepatocellular carcinoma in non-viral-related chronic liver disease has gradually increased in Japan. Obesity and diabetes mellitus type 2 have been established as a significant risk factor for hepatocellular carcinoma (HCC) by epidemiologic observations and experimental studies. The risks of these factors for HCC are likely conferred by two factors: the increased risk for development of non-alcoholic steatohepatitis (NASH) and the carcinogenic potential of themselves. Hepatocellular carcinoma in NASH is difficult to evaluate because histological diagnosis is required for diagnosis of NASH, which can lead selection bias. Furthermore, end-stage NASH is in effect "burned-out" NASH, for which the diagnosis of NASH cannot be made any more. At all events, previous studies on the etiology of Japanese HCC showed that non-alcoholic fatty liver disease accounts for 1-5% of all HCC (male predominant, median age 72 years). They have high prevalences of obesity and/or diabetes mellitus type 2 and 10-75% of the HCC arose from non-cirrhotic livers. HCC in NASH may be of multicentric origin, similar to HCC based on viral hepatitis. Regular screening for HCC is extremely important especially in cirrhotic NASH patients and recurrence should be warned. In western and Asian countries, the prevalence of non-alcoholic fatty liver disease in the general population is increasing dramatically. Therefore, there is an urgent need to elucidate pathogenesis and clinical features of HCC in NASH. In this review we summarize current concepts for HCC in NASH.

Risk of cancer in patients on insulin glargine and other insulin analogues in comparison with those on human insulin: results from a large population-based follow-up study

AIMS/HYPOTHESIS

Several publications suggest an association between certain types of insulin and cancer, but with conflicting results. We investigated whether insulin glargine (A21Gly,B31Arg,B32Arg human insulin) is associated with an increased risk of cancer in a large population-based cohort study.

METHODS

Data for this study were obtained from dispensing records from community pharmacies individually linked to hospital discharge records from 2.5 million individuals in the Netherlands. In a cohort of incident users of insulin, the association between insulin glargine and other insulin analogues, respectively, and cancer was analysed in comparison with human insulin using Cox proportional hazard models with cumulative duration of drug use as a time-varying determinant. The first hospital admission with a primary diagnosis of cancer was considered as the main outcome; secondary analyses were performed with specific cancers as outcomes.

RESULTS

Of the 19,337 incident insulin users enrolled, 878 developed cancer. Use of insulin glargine was associated with a lower risk of malignancies in general in comparison with human insulin (HR 0.75, 95% CI 0.71, 0.80). In contrast, an increased risk was found for breast cancer (HR 1.58, 95% CI 1.22, 2.05). Dose-response relationships could not be identified.

CONCLUSION/INTERPRETATION

Users of insulin glargine and users of other insulin analogues had a lower risk of cancer in general than those using human insulin. Both associations might be a consequence of residual confounding, lack of adherence or competing risk. However, as in previous studies, we demonstrated an increased risk of breast cancer in users of insulin glargine in comparison with users of human insulin.

Type 2 diabetes and hepatocellular carcinoma: a case-control study in patients with chronic hepatitis B

Type 2 diabetes has been suggested as an independent risk factor for the development of hepatocellular carcinoma (HCC). However, the role of Type 2 diabetes on the development of HCC in the presence of chronic hepatitis B (CHB) remains inconclusive. We conducted this hospital-based case-control study to evaluate the roles of Type 2 diabetes in HCC development in patients with CHB. From January 2004 to December 2008, a total of 6,275 eligible consecutive patients with chronic hepatitis B virus (HBV) infection were recruited. A total of 1,105 of them were patients with HBV-related HCC and 5,170 patients were CHB but without HCC. We used multivariate logistic regression models to investigate the association between Type 2 diabetes and HCC risk. The prevalence of Type 2 diabetes is higher among HCC patients without cirrhosis than among those with cirrhosis (12.1% vs. 6.7%, p=0.003). Type 2 diabetes was associated with a significantly high risk of HCC in female patients after adjusting for age, family history of HCC, city of residence, hepatitis B e antigen and cirrhosis with an odds ratio (95% confidence interval, CI) of 1.9 (1.1-3.4). Restricted analyses among female patients without cirrhosis indicated that Type 2 diabetes was strongly associated with HCC risk with adjusted odds ratio (95% CI) of 5.6 (2.2-14.1). In conclusion, Type 2 diabetes is independently associated with the increased risk of HCC in female CHB patients. Female CHB patients with Type 2 diabetes are of a high HCC risk population and should be considered for HCC close surveillance program.

Metformin as an antitumor agent in cancer prevention and treatment

Recent epidemiological investigations conducted in diabetic cohorts and cancer patients have found that metformin users have lower risks for cancer than those using insulin or insulin secretagogues. Studies conducted in various animal tumor models and cancer cell lines have demonstrated that metformin prevents tumor development or inhibits cell proliferation. In addition, a recent clinical trial has shown that short-term use of metformin reduces aberrant crypt foci (ACF) formation in non-diabetic patients with ACF. The antitumor activity of metformin may be mediated through its regulatory effect on hormonal, metabolic, and immune functions. Metformin achieves glycemic control by reducing hepatic glucose production and increasing the muscle intake of glucose, thus lowering levels of circulating glucose and, consequently, insulin. The major molecular targets of metformin are the liver kinase B1 (LKB1)-AMP-activated protein kinase (AMPK) signaling and mammalian target of rapamycin (mTOR) pathways, which are central in the regulation of cellular energy homeostasis and play a crucial role in the control of cell division and cell proliferation. Metformin has been shown to improve endothelial function, decrease inflammatory activity, and regulate immune function. Increasing experimental evidence provides a strong biological rationale for metformin as an antitumor and chemopreventive agent. Metformin is being tested as an adjuvant cancer therapy in clinical settings, and metformin is recommended for all cases of Type 2 diabetes without contraindications. As described in this review, the chemopreventive value of metformin is not restricted to diabetic or obese individuals.

Metformin: a new option in cancer treatment

Metformin is a biguanine, the most widely used antidiabetic drug for the treatment of type 2 diabetes. Some studies suggest that metformin decreases the incidence of cancer and cancer-related mortality in diabetic patients. Metformin activates the AMP-activated protein kinase (AMPK) pathway, a major sensor of the energy status of the cell and an inhibitor of mammalian target of rapamycin (mTOR) catalytic activity, inducing a decrease in blood glucose by decreasing hepatic gluconeogenesis and stimulating glucose uptake in the muscle. Some preclinical data supports the inhibition of tumour cancer cell growth associated with mTOR inhibition and a decrease in phosphorylation of S6K, rpS6 and 4E-BP1. Here we have summarised some of the preclinical data and data of many clinical trials that are exploring the true value of metformin for cancer patients, mainly breast and prostate cancer.

Insulin therapy in diabetes and cancer risk: current understanding and implications for future study: proceedings from a meeting of a European Insulin Safety Consensus Panel, convened and sponsored by Novo Nordisk, held Tuesday October 5, 2010 at The Radisson Edwardian Heathrow Hotel, Hayes, Middlesex, UK

INTRODUCTION

Interest in the possibility of certain insulin treatments having the potential to modify cancer development and prognosis was reawakened in 2009, following publication of several epidemiological studies addressing this issue. This interest extends to how diabetes itself and cancer might be linked, and makes desirable an exchange of expert views and knowledge to enhance understanding in this subject among those treating diabetes and cancer, or those developing diabetes therapies.

METHODS

A European meeting was convened with participants invited based on known relevant interests in endocrinology, oncology, epidemiology, and insulin analog design and investigation. Experts in these fields were invited to present on relevant topics, with open discussions held after each presentation.

RESULTS

Concern over the potential mitogenic properties of certain insulin analogs has arisen from some (but not all) epidemiological studies, although confounding factors render interpretation controversial. Future epidemiological studies are likely to strengthen confidence in drawing conclusions. Meanwhile, pharmacological studies, and a consideration of cancer pathophysiology, implicate increased insulin-like growth factor-1 receptor affinity, and/or deranged insulin receptor interaction/signaling properties as possible a priori causes for concern with some insulin analogs. Again, interpretation of the body of pharmacological evidence is confounded by the array of test systems and methodologies used, and by studies frequently succumbing to methodological pitfalls. Reassuringly, most available insulin analogs do not differ in their receptor interaction response profile to human insulin, and for those that do there are reasons to question any potential clinical relevance. Nevertheless, it is desirable that new experimental models are devised that can better determine the likely clinical consequences of any variance in receptor response profile versus human insulin.

CONCLUSION

More data are required to increase our understanding of this issue. To facilitate and disseminate such understanding, close cooperation and communication between diabetologists, epidemiologists, oncologists, and insulin engineers will be essential.

Diabetes and risk of tumors: oncologic considerations

Type 2 diabetes mellitus and malignant tumors are frequent diseases worldwide. The incidence of these two diseases is growing continuously and causes serious health care problem. Population based epidemiologic studies show that the coexistence of type 2 diabetes and malignant tumors is more frequent than expected by the age-corrected incidence and prevalence of each disease. Epidemiologic studies and meta-analyses show that type 2 diabetes increases the risk and tumor specific mortality of certain cancers. The overlapping risk factors of the diseases suggest a relationship between type 2 diabetes and malignant tumors, with a significant role of obesity as a major risk factor. In the pathophysiology of type 2 diabetes there are several biological processes, which may explain the higher cancer risk in type 2 diabetes. In vitro experiments, and in vivo animal studies show that the mitotic effect of hyperinsulinemia plays an important role in the relationship of cancer and type 2 diabetes mellitus. Recent studies show that the different treatment modalities, antidiabetic drugs and their combinations used for the treatment of type 2 diabetes can modify cancer risk. The majority of the data show that metformin therapy decreases, while insulin secretagog drugs slightly increase the risk of certain types of cancers in type 2 diabetes. Metformin can decrease cell proliferation and induce apoptosis in certain cancer cell lines. Endogenous and exogenous (therapy induced) hyperinsulinemia may be mitogenic and may increase the risk of cancer in type 2 diabetes. Human studies showed that the analogue insulin glargin increases the risk of certain cancers. As a result of conceptual weaknesses in study design, data collection, and statistical methods the results of these studies are questionable. According to present knowledge, obtaining and maintaining optimal metabolic target values with the appropriate choice of treatment modality is the aim of treatment in type 2 diabetes. Presently, study results showing elevated mitogenic potential with some antidiabetic treatment modalities are not taken into account, when considering the choice of antidiabetic treatment in type 2 diabetic patients. In the care of patients with increased cancer risk, oncologic considerations should be taken into account. Well designed, prospective, clinical studies would be necessary to demonstrate the possible correlation between treatment modalities of type 2 diabetes and change of cancer risk in type 2 diabetes mellitus. Orv. Hetil., 2011, 152, 1144–1155.

Cancer risk in type 2 diabetes mellitus: metabolic links and therapeutic considerations

Type 2 diabetes mellitus (DM2) is increasing in incidence, creating worldwide public health concerns and impacting morbidity and mortality rates. An increasing number of studies have demonstrated shared associations between DM2 and malignancy, including key clinical, biochemical, and metabolic commonalities. This paper will attempt to explore the relationship between the various types of cancer and diabetes, the common metabolic pathways underlying cancer development, and the potential impact of various antidiabetes therapies on cancer risk.

Liver fibrogenesis and metabolic factors

Mechanisms of liver fibrosis are complex and varied. Among them, metabolic factors are particularly important in the development of fibrosis associated with nonalcoholic steatohepatitis (NASH). These factors are some of the "multiple parallel hits" responsible for liver damage during NASH. Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome. Major profibrogenic protagonists, such as hepatic stellate cells and Kupffer cells, are activated by insulin resistance, apoptosis and local inflammation. Relations between steatosis, insulin resistance and fibrosis are complex. Initially, simple steatosis may be a way to store deleterious free fatty acid in neutral triglycerides. If the lipid storage threshold is exceeded, steatosis may become associated with lipotoxicity. Similarly, interindividual variations of adipose tissue expandability might explain various phenotypes, ranging from "metabolically obese patients with normal weight" to "metabolically normal morbidly obese patients". The metabolic abnormalities in subcutaneous and visceral adipose tissue are insulin resistance and low-grade inflammation, which are associated with increased release of free fatty acid flux and changes in adipocytokines production such as leptin, adiponectin and interleukin 6. The nuclear transcription factor peroxisome proliferator-activated receptor gamma (PPARγ) and the endocannabinoid system might have important roles in liver fibrogenesis and are potential therapeutic targets. Finally, with the development of new molecular tools, gut microbiota has been recently identified for its pleiotropic functions, including metabolism regulation. Better knowledge of these mechanisms should lead to new strategies for the treatment of metabolic factors that play a key role in liver injuries.

Insulin resistance and chronic liver disease

Increased insulin resistance is frequently associated with chronic liver disease and is a pathophysiological feature of hepatogenous diabetes. Distinctive factors including hepatic parenchymal cell damage, portal-systemic shunting and hepatitis C virus are responsible for the development of hepatogenous insulin resistance/diabetes. Although it remains unclear whether insulin secretion from pancreatic beta cells is impaired as it is in type 2 diabetes, retinopathic and cardiovascular risk is low and major causes of death in cirrhotic patients with diabetes are liver failure, hepatocellular carcinoma and gastrointestinal hemorrhage. Hemoglobin A1c is an inaccurate marker for the assessment and management of hepatogenous diabetes. Moreover, exogenous insulin or sulfonylureas may be harmful because these agents may promote hepatocarcinogenesis. Thus, pathogenesis, cause of death, assessment and therapeutic strategy for hepatogenous insulin resistance/diabetes differ from those for lifestyle-related type 2 diabetes. In this article, we review features of insulin resistance in relationship to chronic liver disease. We also discuss the impact of anti-diabetic agents on interferon treatment and hepatocarcinogenesis.

Diabetes and cancer

Diabetes and cancer are common conditions, and their co-diagnosis in the same individual is not infrequent. A link between the two conditions has been postulated for almost 80 years, but only in the past decade has significant epidemiological evidence been amassed to suggest that diabetes and cancer are associated, and the link appears causal. Hyperinsulinaemia, adipocytokines, growth factors and epigenetic changes may be implicated in the pathogenesis of cancer amongst patients with diabetes, and recently, diabetes therapies have also been implicated. There is reasonable circumstantial evidence that metformin may decrease the risk of cancer amongst diabetic patients. Much more research is required to elucidate the link between diabetes and cancer, particularly the potential link with diabetes treatments.

[Hepatitis C virus infection and hepatocarcinogenesis]

It is evidenced that both HBV and HCV infections may cause chronic hepatitis, liver cirrhosis and hepatocellular carcinoma (HCC). HCV is considered as an oncogen virus. The mechanism of carcinogenesis in case of the two distinct viruses shows a number of common and different features. HCC usually develops in stage of liver cirrhosis caused by chronic inflammation of many years or decades. In contrast to HBC, HCV will not be incorporated into the genome of hepatocytes. It induces throughout different mechanisms the development of cancer cells, which will proliferate out of control. Before the discovery of HCV, the connection of non-A non-B (NANB) hepatitis and liver cancer has yet been observed. The subsequent epidemiological studies confirmed this association. A number of publications prove that HCC may develop without cirrhosis in HCV infected patients. The exact mechanism is not known, but data indicate that some proteins of the virus may induce oncogenic process. Differences were found in HCV core gene between HCC patients with and without cirrhosis. It is postulated that the virus evolves its oncogenic effect via endoplasmic and oxidative stress, further on by activation of different oncogenic signal pathways. Recent publications indicate the role of virus induced insulin resistance. Besides the virus determined factors, the host reaction, the deficient tumor cell eliminating capacity may also have a role in the development of liver carcinoma. Monitoring of HCV infected patients for HCC is an important clinical issue. Most relevant is the regular ultrasound cheek up. Serum alpha fetoprotein level is elevated only in a smaller proportion of the patients. The treatment protocol of HCV induced HCC does not differ from the others developed in non-HCV liver diseases.

Metformin and cancer risk in diabetic patients: a systematic review and meta-analysis

Metformin, an insulin-lowering agent, has been associated with decreased cancer risk in epidemiologic studies in diabetic patients. We performed a comprehensive literature search and meta-analysis of epidemiologic studies to assess the effect of metformin on cancer incidence and mortality in diabetic patients, using Pubmed, ISI Web of Science, Embase, and the Cochrane library until May 2009, with no language or time restrictions. Independent reports with sufficient information to allow risk estimation of cancer risk/mortality and a measure of uncertainty were reviewed and cross-checked independently by three investigators. Eleven studies were selected for relevance in terms of intervention, population studied, independence, and reporting of cancer incidence or mortality data, reporting 4,042 cancer events and 529 cancer deaths. A 31% reduction in overall summary relative risk (0.69; 95% confidence interval, 0.61-0.79) was found in subjects taking metformin compared with other antidiabetic drugs. The inverse association was significant for pancreatic and hepatocellular cancer, and nonsignificant for colon, breast, and prostate cancer. A trend to a dose-response relationship was noted. Metformin is associated with a decreased risk of cancer incidence compared with other treatments among diabetic patients. Given the retrospective nature of most studies and the possibility that the control treatments increase risk, phase II trials are needed before large cancer prevention trials are launched.