SynthesisPloS one2013
Metformin therapy and risk of cancer in patients with type 2 diabetes: systematic review.
Synthesis in PloS one, 2013. The graph read 7 numbers from its abstract, feeding 2 cells of the map, but none could be read as for or against, so it casts no vote. It also reports 7 associations that do not count as treatment evidence, such as OR 0.56 (0.36 to 0.86) for adverse events & safety. Cited by 222 papers, 13 of them syntheses that pooled it.
What it found
Each row is one number read from the abstract, on the scale the paper reported it, with its interval. Left of the dashed line favours the treatment, right favours the comparator. Under each row is the sentence it came from. New to these charts? A ten-minute tutorial.
Read, but not usablea number the graph found but could not read as for or against
In observational studies there was a significant association of exposure to metformin with the risk of cancer death [6 studies, 24,410 patients, OR:0.65, 95%CI: 0.53-0.80], all malignancies [18 studies, 561,836 patients, OR:0.73, 95%CI: 0.61-0.88], liver [8 studies, 312,742 patients, OR:0.34; 95%CI: 0.19-0.60] colorectal [12 studies, 871,365 patients, OR:0.83, 95%CI: 0.74-0.92], pancreas [9 studies, 847,248 patients, OR:0.56, 95%CI: 0.36-0.86], stomach [2 studies, 100701 patients, OR:0.83, 95%CI: 0.76-0.91], and esophagus cancer [2 studies, 100694 patients, OR:0.90, 95%CI: 0.83-0.98].
In observational studies there was a significant association of exposure to metformin with the risk of cancer death [6 studies, 24,410 patients, OR:0.65, 95%CI: 0.53-0.80], all malignancies [18 studies, 561,836 patients, OR:0.73, 95%CI: 0.61-0.88], liver [8 studies, 312,742 patients, OR:0.34; 95%CI: 0.19-0.60] colorectal [12 studies, 871,365 patients, OR:0.83, 95%CI: 0.74-0.92], pancreas [9 studies, 847,248 patients, OR:0.56, 95%CI: 0.36-0.86], stomach [2 studies, 100701 patients, OR:0.83, 95%CI: 0.76-0.91], and esophagus cancer [2 studies, 100694 patients, OR:0.90, 95%CI: 0.83-0.98].
In observational studies there was a significant association of exposure to metformin with the risk of cancer death [6 studies, 24,410 patients, OR:0.65, 95%CI: 0.53-0.80], all malignancies [18 studies, 561,836 patients, OR:0.73, 95%CI: 0.61-0.88], liver [8 studies, 312,742 patients, OR:0.34; 95%CI: 0.19-0.60] colorectal [12 studies, 871,365 patients, OR:0.83, 95%CI: 0.74-0.92], pancreas [9 studies, 847,248 patients, OR:0.56, 95%CI: 0.36-0.86], stomach [2 studies, 100701 patients, OR:0.83, 95%CI: 0.76-0.91], and esophagus cancer [2 studies, 100694 patients, OR:0.90, 95%CI: 0.83-0.98].
In observational studies there was a significant association of exposure to metformin with the risk of cancer death [6 studies, 24,410 patients, OR:0.65, 95%CI: 0.53-0.80], all malignancies [18 studies, 561,836 patients, OR:0.73, 95%CI: 0.61-0.88], liver [8 studies, 312,742 patients, OR:0.34; 95%CI: 0.19-0.60] colorectal [12 studies, 871,365 patients, OR:0.83, 95%CI: 0.74-0.92], pancreas [9 studies, 847,248 patients, OR:0.56, 95%CI: 0.36-0.86], stomach [2 studies, 100701 patients, OR:0.83, 95%CI: 0.76-0.91], and esophagus cancer [2 studies, 100694 patients, OR:0.90, 95%CI: 0.83-0.98].
In observational studies there was a significant association of exposure to metformin with the risk of cancer death [6 studies, 24,410 patients, OR:0.65, 95%CI: 0.53-0.80], all malignancies [18 studies, 561,836 patients, OR:0.73, 95%CI: 0.61-0.88], liver [8 studies, 312,742 patients, OR:0.34; 95%CI: 0.19-0.60] colorectal [12 studies, 871,365 patients, OR:0.83, 95%CI: 0.74-0.92], pancreas [9 studies, 847,248 patients, OR:0.56, 95%CI: 0.36-0.86], stomach [2 studies, 100701 patients, OR:0.83, 95%CI: 0.76-0.91], and esophagus cancer [2 studies, 100694 patients, OR:0.90, 95%CI: 0.83-0.98].
In observational studies there was a significant association of exposure to metformin with the risk of cancer death [6 studies, 24,410 patients, OR:0.65, 95%CI: 0.53-0.80], all malignancies [18 studies, 561,836 patients, OR:0.73, 95%CI: 0.61-0.88], liver [8 studies, 312,742 patients, OR:0.34; 95%CI: 0.19-0.60] colorectal [12 studies, 871,365 patients, OR:0.83, 95%CI: 0.74-0.92], pancreas [9 studies, 847,248 patients, OR:0.56, 95%CI: 0.36-0.86], stomach [2 studies, 100701 patients, OR:0.83, 95%CI: 0.76-0.91], and esophagus cancer [2 studies, 100694 patients, OR:0.90, 95%CI: 0.83-0.98].
In observational studies there was a significant association of exposure to metformin with the risk of cancer death [6 studies, 24,410 patients, OR:0.65, 95%CI: 0.53-0.80], all malignancies [18 studies, 561,836 patients, OR:0.73, 95%CI: 0.61-0.88], liver [8 studies, 312,742 patients, OR:0.34; 95%CI: 0.19-0.60] colorectal [12 studies, 871,365 patients, OR:0.83, 95%CI: 0.74-0.92], pancreas [9 studies, 847,248 patients, OR:0.56, 95%CI: 0.36-0.86], stomach [2 studies, 100701 patients, OR:0.83, 95%CI: 0.76-0.91], and esophagus cancer [2 studies, 100694 patients, OR:0.90, 95%CI: 0.83-0.98].
clause the extractor read what became the number
Where it lands on the map
Rows are treatments, columns are outcomes. The coloured squares are the cells this paper feeds, coloured by the vote it casts there. Click one to jump to what this paper adds to it.
What it adds to each cell
For every cell the paper feeds: the belief in the claim with and without this paper, and this paper's estimate drawn against every other readable study in the cell. The ringed dot is this paper.
Metformin×adverse events & safety
No readable resultOpen on the map →What to test next →22 readable studies in this cell: 9 favour the treatment, 8 find no difference, 5 favour the comparator.
This paper's own estimate is on a different scale from the rest of the cell, so it is not drawn here.
Metformin×pharmacokinetics & dosing
No readable resultOpen on the map →What to test next →2 readable studies in this cell: 0 favour the treatment, 2 find no difference, 0 favour the comparator.
This paper's own estimate is on a different scale from the rest of the cell, so it is not drawn here.
The trial behind it
Trials whose registry record cites this paper, or whose number appears in the abstract. A trial that started after this paper was published is citing it as background, not reporting it.
Neither the registry nor the abstract names a trial number. If this is a trial report, that itself is worth knowing.
Who cites it
222 citing papers in PubMed, 13 syntheses or guidelines pooled it, 425 citations in OpenAlex.
- Metformin: A Dual-Role Player in Cancer Treatment and Prevention: A Comprehensive Systematic Review and Meta-Analysis.Medicina (Kaunas, Lithuania) · 2025Pooled it
- Association of metformin use with risk and survival outcome of esophageal cancer in patients with diabetes: A systematic review and meta-analysis.PloS one · 2025 · on this mapPooled it
- Impact of metformin on melanoma: a meta-analysis and systematic review.Frontiers in oncology · 2024Pooled it
- Metformin Use on Incidence and Oncologic Outcomes of Bladder Cancer Patients With T2DM: An Updated Meta-Analysis.Frontiers in pharmacology · 2022Pooled it
- Medication use and risk of proximal colon cancer: a systematic review of prospective studies with narrative synthesis and meta-analysis.Cancer causes & control : CCC · 2021Pooled it
- The Potential Effect of Metformin on Cancer: An Umbrella Review.Frontiers in endocrinology · 2019Pooled it
- Pioglitazone and bladder cancer risk: a systematic review and meta-analysis.Cancer medicine · 2018Pooled it
- Metformin, Asian ethnicity and risk of prostate cancer in type 2 diabetes: a systematic review and meta-analysis.BMC cancer · 2018 · on this mapPooled it
- Metformin and cancer in type 2 diabetes: a systematic review and comprehensive bias evaluation.International journal of epidemiology · 2017Pooled it
- Metformin therapy and risk of colorectal adenomas and colorectal cancer in type 2 diabetes mellitus patients: A systematic review and meta-analysis.Oncotarget · 2017 · on this mapPooled it
- Systematic Review with Network Meta-Analysis: Antidiabetic Medication and Risk of Hepatocellular Carcinoma.Scientific reports · 2016Pooled it
- Pharmacologic Therapy of Diabetes and Overall Cancer Risk and Mortality: A Meta-Analysis of 265 Studies.Scientific reports · 2015 · on this mapPooled it
- Impact of metformin on clinical outcomes among men with prostate cancer: a systematic review and meta-analysis.Prostate cancer and prostatic diseases · 2015Pooled it
- Effects of metformin on transcriptomic and metabolomic profiles in breast cancer survivors enrolled in the randomized placebo-controlled MetBreCS trial.Scientific reports · 2025Trial
- Impact of metformin use on the recurrence of hepatocellular carcinoma after initial liver resection in diabetic patients.PloS one · 2021Trial
- Effectiveness of Metformin in Preventing Colorectal Cancer Among Japanese Patients With Type 2 Diabetes: A Target Trial Emulation.Pharmacoepidemiology and drug safety · 2026Article
- Metformin in gastrointestinal cancers and inflammatory bowel disease: Unraveling its mechanisms and therapeutic applications.iScience · 2026Review
- Article
- Close multilevel links between metabolic dysfunction-associated steatotic liver disease and type 2 diabetes mellitus.Metabolism open · 2025Review
- Alteration of metabolic activity regulates mitochondrial temperature in diagnosis in HepG2 hepatocellular carcinoma cells.Scientific reports · 2025Article
162 more citing papers are in PubMed but not listed here.
Corrections and comments
PubMed lists nothing against this paper. Absence here is not a guarantee, only a check that was made.
Authors and funding
6 authors at 3 institutions in 2 countries.
Funding
No grant is acknowledged in the PubMed record.
Abstract
The marked sentences are the ones the graph read a number from.
aims/hypothesisDiabetes treatments were related with either an increased or reduced risk of cancer. There is ongoing debate about a potential protective action of metformin. To summarize evidence on the association between metformin and risk of cancer and cancer mortality in patients with diabetes.
methodsDATA SOURCE: MEDLINE and EMBASE (January 1966-April 2012). We selected randomized studies comparing metformin and other hypoglycaemic agents and observational studies exploring the association between exposure to metformin and cancer. Outcomes were cancer mortality, all malignancies and site-specific cancers.
resultsOf 25307 citations identified, 12 randomized controlled trials (21,595 patients) and 41 observational studies (1,029,389 patients) met the inclusion criteria. In observational studies there was a significant association of exposure to metformin with the risk of cancer death [6 studies, 24,410 patients, OR:0.65, 95%CI: 0.53-0.80], all malignancies [18 studies, 561,836 patients, OR:0.73, 95%CI: 0.61-0.88], liver [8 studies, 312,742 patients, OR:0.34; 95%CI: 0.19-0.60] colorectal [12 studies, 871,365 patients, OR:0.83, 95%CI: 0.74-0.92], pancreas [9 studies, 847,248 patients, OR:0.56, 95%CI: 0.36-0.86], stomach [2 studies, 100701 patients, OR:0.83, 95%CI: 0.76-0.91], and esophagus cancer [2 studies, 100694 patients, OR:0.90, 95%CI: 0.83-0.98]. No significant difference of risk was observed in randomized trials. Metformin was not associated with the risk of: breast cancer, lung cancer, ovarian cancer, uterus cancer, prostate cancer, bladder cancer, kidney cancer, and melanoma. CONCLUSIONS/
interpretationResults suggest that Metformin might be associated with a significant reduction in the risk of cancer and cancer-related mortality. Randomized trials specifically designed to evaluate the efficacy of metformin as an anticancer agent are warranted.
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What Socratic holds
Registered trials
Read under generation 80e0d062 · epoch 390. Bibliography from PubMed, PubMed Central and OpenAlex; grants from NIH RePORTER; trial links from ClinicalTrials.gov; estimates, votes and beliefs from the Socratic graph.