Evidence map›Paper›PMID 28031313›Full record

SynthesisInternational journal of epidemiology2017

Metformin and cancer in type 2 diabetes: a systematic review and comprehensive bias evaluation.

Ruth E Farmer, Deborah Ford, Harriet J Forbes, Nishi Chaturvedi, Richard Kaplan, Liam Smeeth, Krishnan Bhaskaran

Erratum issuedFull text readMeta-AnalysisSystematic Review
PubMed Full text at PMC Publisher
In one paragraph

Synthesis in International journal of epidemiology, 2017. The graph could read no effect estimate from its abstract, so it casts no vote on the map. An erratum has been issued. Cited by 26 papers, 2 of them syntheses that pooled it.

0numbers the graph read from it
0cells of the map it votes in
26citing papers in PubMed, 2 pooled it
–field-weighted citation impact
1 · What the graph read from 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.

The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.

2 · The registry

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.

3 · Its place in the literature

Who cites it

26 citing papers in PubMed, 2 syntheses or guidelines pooled it.

  1. Pooled it
  2. American Association of Clinical Endocrinology Clinical Practice Guideline: Developing a Diabetes Mellitus Comprehensive Care Plan-2022 Update.Endocrine practice : official journal of the American College of Endocrinology and the American Association of Clinical Endocrinologists · 2022
    Guideline
  3. Article
  4. Review
  5. Article
  6. Review
  7. Article
  8. Metformin: A Dual-Role Player in Cancer Treatment and Prevention.International journal of molecular sciences · 2024
    Review
  9. Review
  10. Review
  11. Review
  12. Article
  13. Article
  14. Article
  15. Observational
  16. Article
  17. Review
  18. Review
  19. Article
  20. Article
4 · The record

Corrections and comments

5 · Who and what money

Authors and funding

7 authors.

Ruth E FarmerDepartment of Non-communicable Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, UK.
Deborah FordMRC Clinical Trials Unit at UCL, London, UK and.
Harriet J ForbesDepartment of Non-communicable Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, UK.
Nishi ChaturvediInstitute of Cardiovascular Science, University College London, London, UK.
Richard KaplanMRC Clinical Trials Unit at UCL, London, UK and.
Liam SmeethDepartment of Non-communicable Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, UK.
Krishnan BhaskaranDepartment of Non-communicable Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, UK.

Funding

Medical Research Council MC_EX_G0800814Medical Research Council MC_EX_UU_G0800814Medical Research Council MC_UU_12023/21Medical Research Council MC_UU_12023/25Medical Research Council MC_UU_12023/28Medical Research Council MR/K006584/1Wellcome Trust 098504/Z/12/ZWellcome Trust 107731/Z/15/Z
6 · The paper itself

Abstract

Background: Existing observational studies provide conflicting evidence for the causal effect of metformin use on cancer risk in patients with type-2 diabetes, and there are concerns about bias affecting a number of studies. Methods: MEDLINE was used to identify observational studies investigating the association between metformin and overall or site-specific cancer in people with type-2 diabetes. A systematic data extraction and bias assessment was conducted, in which risk of eight bias domains (outcome, exposure, control selection, baseline confounding, time-dependent confounding, immortal time, missing data, censoring methods) were assessed against pre-defined criteria, and rated as unlikely, low, medium or high. Results: Of 46 studies identified, 21 assessed the effect of metformin on all cancer. Reported relative risks ranged from 0.23 to 1.22, with 12/21 reporting a statistically significant protective effect and none a harmful effect. The range of estimates was similar for site-specific cancers; 3/46 studies were rated as low or unlikely risk of bias in all domains. Two of these had results consistent with no effect of metformin; one observed a moderate protective effect overall, but presented further analyses that the authors concluded were inconsistent with causality. However, 28/46 studies were at risk from bias through exposure definition, 22 through insufficient baseline adjustment and 35 from possible time-dependent confounding. Conclusions: Observational studies on metformin and cancer varied in design, and the majority were at risk of a range of biases. The studies least likely to be affected by bias did not support a causal effect of metformin on cancer risk.

Indexed as

BiasDiabetes Mellitus, Type 2HumansHypoglycemic AgentsMetforminNeoplasmsObservational Studies as TopicHypoglycemic AgentsMetforminbiascancercausalityconfoundingdiabetesPharmacoepidemiology

Identifiers

PMID28031313
PMCPMC5837266

What Socratic holds

Textfull text, public
LicenceCC BY
Read underepoch 390

Registered trials

None linked

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.