Metformin Use in Adolescents: Old and New Therapeutic Perspectives

Metformin (1,1-dimethylbiguanide) is the most widely used drug to treat type 2 diabetes, and is one of only two oral antidiabetic drugs on the World Health Organization (WHO) list of essential medicines [1]. Its history can be traced back to the use of Galega officinalis as a herbal medicine in medieval Europe. Its name derives from gale (milk) and ega (to bring on), as Galega has been used as a galactogogue in small domestic animals (hence the name “Goat’s rue”). Studies in the late 1800s indicated that Galega officinalis was rich in guanidine and in 1918 guanidine was shown to possess hypoglycaemic activity in animals. Jean Sterne was the first to investigate dimethylbiguanide (Metformin) for clinical development and proposed the name ‘Glucophage’ (glucose eater) and published his results in 1957 [2-4].


Introduction
Metformin (1,1-dimethylbiguanide) is the most widely used drug to treat type 2 diabetes, and is one of only two oral antidiabetic drugs on the World Health Organization (WHO) list of essential medicines [1]. Its history can be traced back to the use of Galega officinalis as a herbal medicine in medieval Europe. Its name derives from gale (milk) and ega (to bring on), as Galega has been used as a galactogogue in small domestic animals (hence the name "Goat's rue"). Studies in the late 1800s indicated that Galega officinalis was rich in guanidine and in 1918 guanidine was shown to possess hypoglycaemic activity in animals. Jean Sterne was the first to investigate dimethylbiguanide (Metformin) for clinical development and proposed the name 'Glucophage' (glucose eater) and published his results in 1957 [2][3][4].
Metformin is the most widely prescribed drug to treat hyperglycemia in individuals with T2DM and is recommended, in conjunction with lifestyle modification (diet, weight control and physical activity), as a first line oral therapy in the recent guidelines of the American Diabetes Association and European Association of the Study of Diabetes. It is effective anti-hyperglycaemic agent that inhibits hepatic glucose production and increases peripheral glucose uptake. Metformin also exerts beneficial effects on circulating lipids and exhibits cardio-protective features in obese patients. Clinical trials suggest that Metformin, that is effective in treating T2DM, may also have therapeutic potential in other conditions in which insulin resistance constitutes part of the pathogenesis, including obesity, prediabetes, polycystic ovary disease, non-alcoholics fatty liver and premature pubarche (Figure 1). Epidemiological studies have shown a decrease in cancer incidence in Metformin-treated patients, suggesting a potential application of the drug as an anti-cancer agent [5].

Mechanism of Action
Although prescribed and used extensively since the end of the precise molecular (or biochemical) mechanism/s of action remain incompletely understood. It acts by countering insulin resistance, particularly in liver and skeletal muscle. It suppresses hepatic gluconeogenesis, increases peripheral insulin sensitivity in insulin sensitive tissues such as muscle and adipose tissue, and enhances peripheral glucose utilization [6][7][8][9]. However, the main effect of Metformin appears to be decreasing hepatic glucose production through a mild inhibition of the mitochondrial respiratory-chain complex 1. This transient decrease in cellular energy status promotes activation of adenosine monophosphate-activated protein (AMPK), a well-known cellular energetic sensor. AMPK is a protein kinase ubiquitously expressed in mammalian tissues and involved in regulating energy balance. Activation of AMPK stimulates adenosine triphosphate (ATP)-producing catabolic pathways, while inhibiting ATP-consuming anabolic pathways, thereby, maintaining cellular energy stores. In skeletal muscle, activation of AMPK increases glucose uptake and lipid oxidation. In adipose tissue, activation of AMPK reduces both lipolysis and lipogenesis [6][7][8][9]. Metformin regulates glucose transporter 4 (GLUT4) translocation through AMPactivated Protein Kinase (AMPK)-mediated Cbl/CAP Signaling. It enhances insulin signaling in insulin-dependent and -independent pathways [10]. In the liver, activation of AMPK inhibits gluconeogenesis and lipid synthesis but increases lipid oxidation. The activated AMPK decreases flux of free fatty acids and inhibits lipolysis, which may indirectly improve insulin sensitivity through reduced lipotoxicity (reduces hepatic lipogenesis) and exert an indirect effect on hepatic insulin sensitivity to control hepatic glucose output. In the heart, Metformin increases fatty acids uptake and oxidation, and increases glucose uptake and glycolysis [9][10][11][12][13][14]. Metformin can also antagonize the action of glucagon, thus reducing fasting glucose levels [15]. In summary, activation of AMPK in skeletal muscle, liver and adipose tissue decreases circulating glucose, lipids, reduces fat accumulation and enhances insulin sensitivity.
Additional action of Metformin action is through induction of a profound shift in the faecal microbial community profile in diabetic mice and it has also been proposed that this may contribute to its mode of action possibly through an effect on Glucagon-like peptide-1 (GLP-1) secretion [16,17]. Moreover, Metformin enhances the expression of the genes encoding the receptors for both GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) in mouse islets and also increases the effects of GIP and GLP-1 on insulin secretion from beta cells. These incretin-sensitising effects of Metformin appear to be mediated by a peroxisome proliferator-activated receptor α-dependent pathway, as opposed to the more commonly ascribed pathway of Metformin action involving AMP-activated protein kinase [18].
The protective effect on the cardiovascular system cannot be fully explained by its blood glucose-lowering properties. These effects may be partly mediated via beneficial effects on circulating markers of endothelial function (vascular cell adhesion molecule-1 [VCAM-1], E-selectin), fibrinolysis (plasminogen activator inhibitor-1 [PAI-1]) and chronic inflammation (C-reactive protein [CRP]) [19,20].

Pharmacological Properties of Metformin
Metformin has a half-life of around five hours and undergoes renal excretion with 90% being eliminated within 24 hours. It can be prescribed as 500 mg or 850 mg tablets. In adults , it can be started at the 500 mg dose and increased in weekly increments until the maximum tolerated dose is achieved, normally 2 g/day [21,22].
The intestinal absorption of Metformin may be primarily mediated by plasma membrane monoamine transporter (PMAT/SLC29A4), which is expressed on the luminal side of the enterocytes. Metformin has an oral bioavailability of 50-60% under fasting conditions, and is absorbed slowly. Peak plasma concentrations (C max ) are reached within one to three hours of taking immediate-release Metformin and four to eight hours with extended-release formulations. Steady state is usually reached in one or two days. Food decreases the extent of and slightly delays the absorption of Metformin, as shown by approximately a 40% lower mean peak plasma concentration. The plasma protein binding of Metformin is negligible. It should be taken with food to reduce the potential for gastrointestinal side effects. Metformin is undetectable in blood plasma within 24 hours of a single oral dose [21,22]. After administration of a single oral Metformin HCl 500 mg tablet with food, geometric mean Metformin Cmax and AUC did not differ between adolescents with T2DM (12 to 16 years of age) and gender-and weightmatched healthy adults (20 to 45 years of age) [23].

Side-effects and Contraindications of Metformin
Gastrointestinal upsets are the main complain associated with Metformin use. However the main side effect of alarm is its association with lactic acidosis particularly in the setting of renal and cardiac impairment. Lactic acidosis associated with Metformin is a rare condition. No patient in the UKPDS study developed lactic acidosis. A systematic review of the risk of lactic acidosis with Metformin found no cases of fatal or non-fatal lactic acidosis in 274 comparative trials and cohort studies, and estimated that the upper limit of the true incidence of lactic acidosis per 100,000 patient years was 5.1 with Metformin and 5.8 without. Most cases of Metformin-associated lactic acidosis documented in the literature happen during periods of tissue hypoxia (myocardial infarction, acute left ventricular failure or septicaemia). The most common symptoms following overdose appear to include vomiting, diarrhea, abdominal pain, tachycardia, drowsiness, and, rarely, hypoglycemia [24]. This gut irritating effect is believed to be mediated through inhibition of serotonin reuptake transporter (SERT) -mediated intestinal reuptake of serotonin resulting in increased intestinal motility and water retention [25].
Although 90% is renally excreted, accumulation is rare in the Metformin enhances insulin signaling in insulin-dependent andindependent pathways.

Metformin
Stimulates AMPK Activation Activates Insulin Signalling

Decreases Lipogenesis Increases Fatty acid oxidation Increases basal glucose uptake
Increases insulindependent glucose uptake Decreased Insulin Resistance   [26][27][28]. Therefore, Metformin should not be given to patients with severe renal impairment, hepatic disease, cardiac or respiratory insufficiency, or who are receiving radiographic contrast materials. Metformin should be temporarily discontinued during a gastrointestinal illness. Hypoglycemia is very uncommon with Metformin monotherapy but has been reported in combination regimens, likely due to Metformin potentiating other therapeutic agents [29].
Long-term use of metformin has been associated with increased homocysteine levels and malabsorption of vitamin B12. Malabsorption of vitamin B12 occurs with metformin in 30% of diabetic subjects. The earliest manifestations are numbness and paresthesias in the feet, which, unless the vitamin B12 deficiency is corrected, can be followed by weakness, ataxia, sphincter disturbance, and changes in mental status. B12 deficiency -associated macrocytic anemia, is often preceded by the development of neuropathy. While the anemia of vitamin B12 deficiency is reversible, the progress of the neuropathy is only arrested and not reversed with initiation of vitamin B12 therapy [30].

Type 2 Diabetes Mellitus (T2DM)
Obesity has dramatically increased in prevalence world-wide among children and adolescents, accompanied by the appearance and increasing prevalence of type 2 diabetes mellitus (T2DM) [31]. Depending on geographic locations, T2DM accounted for 8-45% of new cases of childhood diabetes [32].
In the treatment of T2 DM in adolescents, Metformin is still the preferred first-line treatment to AAP clinical practice guidelines 2013 [33]. Metformin should be initiated for adolescents who present with mild hyperglycemia (random venous or plasma blood glucose concentrations <250 mg/dL) and HbA1c less than 9% at the time of diagnosis with a concomitant initiation of lifestyle modification program, including nutrition and physical activity [33].
Metformin has proved to be effective and safe with multiple metabolic and cardiovascular benefits. Metformin was approved in Canada in 1972, but did not receive approval by the U.S. Food and Drug Administration (FDA) for T2DMuntil 1994. Glucophage was the first branded formulation of Metformin to be marketed in the United States, beginning on 1995. It has been approved by the Food and Drug Administration (FDA) for children with T2DM aged 10 years and older [34].
The International Society of Pediatric Diabetes (ISPAD) recommended Metformin as the first drug to be used in children with T2DM because of its advantages over sulfonylureas. Metformin has lower risk of developing hypoglycemia, decreases or stabilizes the weight and decreases LDL-C and triglyceride level [35].
However recent data from the TODAY study (Treatment Options for T2DM in Adolescents and Youth) have showed some discouraging results because 52% of adolescents with recent-onset T2DM treated with Metformin alone manifested treatment failure within few years after diagnosis, implying that most youth with T2DM will require multiple oral agents or insulin therapy shortly after diagnosis [36].

Obesity, insulin resistance and prediabetes
Rates of childhood overweight and obesity have nearly tripled in the U.S. and western countries over the last 30 years. Concomitant with the rise in prevalence of childhood obesity there has been a corresponding increase in the incidence of cardiovascular risk factors, such as insulin resistance, prediabetes or impaired glucose tolerance (IGT), T2DM, hypertension, hyperlipidemia and non-alcoholic fatty liver disease (NAFLD) [34,37].
Lifestyle intervention is recommended as the primary treatment for childhood obesity. However, the long-term outcomes of lifestyle interventions for childhood obesity carried out in a clinical-practice setting have varied widely. Low rate of success in many trials promoted an interest in pharmacological interventions and bariatric surgery to prevent diabetes among obese children and adolescents [37].
According to many studies the major effect of Metformin may be through inhibition of appetite probably by increasing the levels of GLP-1 and by interacting with signaling of other hormones or cytokines (such as ghrelin, leptin and insulin) [33][34][35]. Reduction of excessive weight gain has a favorable effect on blood pressure, glycemic control and lipid metabolism [34,[38][39][40].
Pediatric randomized, controlled trial studies have shown improvement in BMI, fasting serum glucose, fasting insulin, homeostasis model assessment-estimated insulin resistance (HOMA-IR) and lipid profile in patients on Metformin therapy for exogenous obesity associated with insulin resistance [41,42]. A systemic review identified 14 randomized controlled trials (RCTs) of Metformin use in non-diabetic obese children and adolescent (aged <18 year) [39]. These RCTs involved a total of 946 children with mean ages from 10 to 16 years. Some included data on glycemic control and most of them involved some sort of lifestyle intervention in addition to the drug with variable follow-up periods. The overall analysis showed a small but significant net body mass index (BMI) reduction of 1.16 kg/m 2 attributable to the drug. Subgroup analysis showed a greater effect for those with a higher BMI at baseline and in younger patients [43].
The 'lifestyle' interventions, which varied greatly between the studies, produced significant BMI reductions in most, and the added effect of Metformin was relatively small. In addition, the effect of Metformin was more apparent in those studies that lasted only 6 months compared to those that continued for a year or more, suggesting a decline in effectiveness over time. Certain ethnic groups and those patients with insulin resistance appeared to have a better benefit with the Metformin use [45][46][47][48][49].
The AACE suggests Metformin to be considered for younger patients who are at moderate to high risk for developing DM; for patients with additional CVD risk factors including hypertension, dyslipidemia, or polycystic ovarian syndrome; for patients with a family history of DM in a first-degree relative; and/or for patients who are obese [50].
In conclusion, Metformin offers significant potential to intervene to reduce or reverse the metabolic and endocrine changes associated with obesity during puberty. However, it appears that publication bias towards trials with positive outcomes has made Metformin appear more effective than it is. Although it is a valuable and useful drug for obese adolescents with insulin resistance but certainly it is not the answer to the obesity epidemic. Larger, long-term studies across different populations are needed to establish the role of Metformin as therapy for obesity and cardio-metabolic risk in young people.

Type 1 diabetes (T1DM) with insulin resistance
Insulin resistance of puberty is well documented in both non diabetic and diabetic adolescents. During puberty increased body fat and BMI correlate strongly with insulin resistance [51,52]. In adolescents with T1DM, it likely plays a role in complicating glycemic control and potentially increasing cardiovascular disease (CVD) risk [53].
In the Diabetes Control and Complications Trial (DCCT), adolescents achieved HbA1c levels that were on average 1% higher than in adults in both the conventional and intensive treatment groups, despite receiving more insulin (units per kilogram body weight) and having increased weight gain. This triad of high HbA1c, high insulin dosage, and weight gain suggests that the insulin administered was less effective in maintaining glycemic control (i.e., insulin resistance) in the adolescent cohort [54,55]. It is observed that although insulin dosages are often increased to overcome the resistance to insulin, the metabolic control often deteriorates during the later stages of pubertal development [56].
The addition of Metformin to insulin therapy in an attempt to improve insulin sensitivity, promote weight control, and reduce insulin dose requirements in patients with T1DM has been assessed in systematic reviews. One systematic review identified nine studies, including both adolescents and adults. The studies compared Metformin versus placebo or another comparator in parallel or crossover design for at least 1 week. Metformin use was associated with reduction in insulin-dose requirement (reductions in total daily insulin of 5.7-10.1 units/day), HbA1c (reductions of 0.6%-0.9%), weight (range of weight loss, 1.7-6.0 kg), and total cholesterol (reduction of 11.6-15.8 mg/dL). Formal estimates of combined effects were possible from five studies which found a significant reduction in insulin dose of 6.6 units/day [57].
Another systematic review compared metformin added to insulin vs insulin therapy alone. In 60 patients the authors found a reduction in HbA1c values when Metformin was added to insulin. One of the studies also showed a 10% decrease in insulin dosage among those taking Metformin. Hypoglycemia and gastrointestinal disturbances were among the most commonly occurring adverse effects of combination therapy [58].
A double blind placebo controlled study was conducted to assess the effects of Metformin on metabolic parameters when added to insulin therapy in 74 pubertal adolescents (ages: 13-20 yr) with T1DM [59]. Participants were randomized to receive either Metformin or placebo for 6 months. Compared to placebo group, Metformin caused significant decrease in total daily insulin dose, BMI z-score and waist circumference at 3 and 6 months compared to baseline, even among normal-weight participants. In the placebo group, total insulin dose and systolic blood pressure increased significantly at 3 months and total insulin dose increased significantly at 6 months. No significant change was observed in HbA1c at any time point between Metformin and placebo groups or within either group [59].
The American Association of Clinical Endocrinologists (AACE) recommended the addition of Metformin and/or insulin in children or adolescents with T2DM when glycemic targets are not achievable with lifestyle measures alone [55].
In conclusion, Metformin is expected to help those overweight adolescence with T1DM who require large doses of insulin, and/or continue to have uncontrolled HbA1c (> 8%) values despite adherence to insulin. However, patients should be made aware that hypoglycemia may become more likely once Metformin is added to their insulin regimen [60].

Non-alcoholic fatty liver disease (NAFLD)
NAFLD is recognized as the most common cause of liver disease in obese children and adolescents. NAFLD includes a wide spectrum of histologic abnormalities ranging from hepatic steatosis to nonalcoholic steato-hepatitis (NASH) that may progressto cirrhosis, and subsequent end stage liver disease and hepatocellular carcinoma [61][62][63].
The first-line treatment of NAFLD is currently based on diet and lifestyle modifications. Most of the published studies in NAFLD population have shown that gradual weight loss (5-10%), calorierestricted diet, and regular physical exercise lead to a decrease in the incidence of metabolic syndrome, improvement in liver enzyme profile, and resolution of hepatic steatosis [64,65]. A pharmacological treatment in patients with NAFLD is not universally accepted yet. However, given that insulin resistance plays a key role in the pathogenesis of NAFLD, many studies have evaluated the use of insulin sensitizers (Metformin and Thiazolidinediones) as a possible treatment for this disease [66]. The potential role of Metformin has also been examined in pediatric patients with NAFLD. Results in pediatric population were similar to those of adults and supported the beneficial effects of Metformin on biochemistry liver profile [65][66][67]. Schwimmer et al. studied 10 obese children and adolescents (8-17 years) with biopsy-proven NASH and elevated alanine aminotransferase (ALT) level). The participant ingested Metformin (1 g/day) for a period of 24 weeks. Metformin caused a significant improvement in alanine aminotransferase (ALT) with a mean change of −86 U/L and normalization in 40% of patients, although weight loss was not achieved. Furthermore, Metformin was effective in reducing liver fat in 90% of subjects as assessed with magnetic resonance spectroscopy [65]. Nadeau et al. randomized fifty obese and insulin-resistant adolescents to receive lifestyle recommendations plus Metformin (850 mg twice a day for 6 months) or placebo. Treatment with Metformin resulted in significant decrease in serum aminotransferases level, liver fat, and increased insulin sensitivity compared with untreated or placebo-treated group [67]. Six open-label trials have evaluated the liver histology modification together with serum aminotransferase levels and insulin resistance markers' amelioration in NAFLD patients treated with Metformin (dose ranging from 1.4 g/day to 2.0 g/day and treatment duration varying from 24 to 48 weeks) alone or in association with other drugs. All these studies reported an improvement in the indices of insulin resistance: five studies reported a reduction in liver function test values and one reported a non-significant increase of these values. In terms of histological improvement, only three trials showed significant differences in inflammation, steatosis, and fibrosis after treatment with Metformin [68][69][70][71][72][73].
A study evaluated the efficacy of the addiction of low dose of Metformin (500 mg twice a day) to dietary treatment (1300 kcal) in 50 obese and nondiabetic patients. Metformin plus dietary therapy was associated with an improvement or even disappearance of hepatic steatosis similar to what observed with diet treatment alone. Metformin treatment was also associated with increased insulin sensitivity and reduced fasting glucose than diet alone [74]. On the other hand, a randomized multicenter placebo controlled trial called the TONIC (Treatment of Nonalcoholic Liver Disease in Children) in which 173 children and adolescents with NAFLD were treated with Metformin (1 g/day) for 96 weeks did not find Metformin superior to placebo in attaining a sustained reduction in ALT levels or significant improvements in histological features [75].
In conclusion, although no drug is currently available as specific treatment for NAFLD, the available evidences clearly show a pivotal role of Metformin in improving metabolic alterations associated with NAFLD. Therefore, Metformin, because of its metabolic effects and its safety profile, remains a promising drug in NAFLD therapy, especially in patients that meet the diagnostic criteria of metabolic syndrome

Polycystic Ovary Syndrome (PCOs)
PCOs is the most common cause of menstrual dysfunction and hyperandrogenism in adolescents [76]. Sultan and Paris recommended that the adolescent girl meet four of the five following criteria: oligoor amenorrhea >2 years after menarche, clinical hyperandrogenism, biochemical hyperandrogenism, insulin resistance or hyperinsulinemia, and polycystic ovaries on ultrasound [77]. Metabolic dysfunction constitutes an important risk associated with PCOs, and it can manifest at an early age. One-third of adolescents with PCOs meet criteria for the metabolic syndrome including (obesity, dyslipidemia, hypertension, and glucose intolerance) compared with approximately 5% of adolescents from the general population [78,79].
One study compared girls with an average age of 12 years who had PCOS to a group of obese, non-hyper-androgenic girls who were matched for age, percent body fat, and abdominal fat. Girls with PCOs were found to have an approximate 50% reduction in peripheral tissue insulin sensitivity compared with controls, and they also exhibited evidence of hepatic insulin resistance and compensatory hyperinsulinemia [80]. A cross-sectional community-based study showed that Obese girls with PCOS were more hirsute, hypertensive, and had significantly higher mean insulin and 2 h post 75 g glucose levels compared with non-obese PCOS [81]. Therefore, using Metformin for PCOS is attractive because this medication is known to improve these variables among adults with PCOS.
Metformin, through peripheral insulin-sensitizing effects, has been shown to exert several beneficial effects in trials of adult women with PCOs when used "off-label" to treat or prevent several clinical problems associated with PCOS including oligomenorrhea, hirsutism, infertility, obesity and glucose abnormalities [82].
A number of studies have demonstrated its efficacy in adolescents with PCOs, but they were short-term studies of 3-6 months in duration and had a limited number of participants [83,84]. One study has compared pre-and post-intervention outcomes of Metformin among 15 adolescents with PCOs. Following 3 months of treatment, glucose tolerance testing and free testosterone levels improved. Metformin suppressed levels of androstenedione and 17-hydroxyprogesterone after an ACTH stimulation test, and authors called for randomized, placebo-controlled trials of Metformin for adolescents with PCOS to confirm their findings [85].
Endocrine society experts recommended that lifestyle management be considered first-line therapy for women with PCOS at increased metabolic risk. They suggest the use of Metformin in women with PCOS who have T2DM or IGT who fail lifestyle modification and for women with PCOS with menstrual irregularity who cannot take or do not tolerate hormonal contraceptives (HCs). In addition it can be used as an adjuvant therapy for infertility to prevent ovarian hyper stimulation syndrome (OHSS) in women with PCOS undergoing in vitro fertilization. They disagree with the use of Metformin for management of hirsutism or acne [86].
Currently, Metformin appears to offer some benefit to adolescents with PCOs, but greater evidence of benefit is required to encourage its wide use by family physicians even if the goals of treatment may evolve with the patient's age.

Premature pubarche
Data indicate that girls with premature pubarche may not have a benign outcome and it may be associated with the metabolic syndrome and this may precede the development of clinical ovarian androgen excess in adolescence [87]. Ibanez et al, showed that 45 percent of postpubertal girls diagnosed with premature pubarche during childhood have an increased incidence of functional ovarian hyperandrogenism, with hirsutism, menstrual disturbances and elevated androgen level [82]. Data suggest a link between the triad of hyperinsulinemia, premature pubarche, and ovarian hyper-androgenism. Hyperinsulinemia is directly related to the degree of androgen excess. The early recognition of girls at risk of developing hyperinsulinaemic androgen excess might enable prevention in childhood [88,89]. In adolescents with premature pubarche, intervention with Metformin, as an insulin sensitizing agent, either as mono-therapy or in combination with the anti-androgen flutamide at low doses, appeared to have some beneficial effects on abdominal adiposity, androgen levels and indices of insulin resistance [90].
Girls born with low birth weight (LBW) and precocious pubarche are more insulin resistant with evidence of increased cardiovascular risk and have an increased incidence of a polycystic ovarian phenotype in young adulthood. Early Meformin therapy for 5 years proved valuable in delaying menarche, augmenting height and reducing total, visceral, and hepatic adiposity and lowering circulating levels of androgens and leptin in these girls compared to late therapy [91,92].

The anti-cancer effect of metformin
Metformin activates AMPK, which directly and indirectly reduces mammalian target of rapamycin (mTOR) complex 1 levels, playing a key role in controlling cell growth, proliferation, and metabolism [93,94]. Many epidemiological, observational and laboratory data suggest an anticancer effect of Metformin in hepatocellular carcinoma, cancer breast and colorectal cancer and others. While others did not find significant anti-cancer effect of using Metformin. Up till now there is no consistent epidemiological evidence in clinical DM trial to support that Metformin is better than other hypoglycemic agent in lowering the cancer incidence. Several early-stage clinical trials are currently under way to investigate metformin's impact on cancer incidence, including colorectal, prostate, endometrial, and breast cancer [95].