ArticleJournal of general internal medicine2019
Metformin and Reduced Risk of Cancer in the Hong Kong Diabetes Registry: Real Effect or Immortal Time Bias?
Article in Journal of general internal medicine, 2019. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 2 papers.
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.
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
2 citing papers in PubMed, 7 citations in OpenAlex.
- Cancer Biology and Prevention in Diabetes.Cells · 2020Review
- Rising Mortality Rate of Cervical Cancer in Younger Women in Urban China.Journal of general internal medicine · 2020Article
Corrections and comments
PubMed lists nothing against this paper. Absence here is not a guarantee, only a check that was made.
Authors and funding
1 author at 1 institution in 1 country.
Funding
No grant is acknowledged in the PubMed record.
Abstract
backgroundWhether metformin reduces cancer risk has been hotly debated. One common opinion is that the observed beneficial effects of metformin are the consequence of immortal time bias.
objectiveTo examine whether the observed beneficial effects of metformin on cancer risk are the consequence of immortal time bias.
designRetrospective cohort study.
participantsA cohort of 3485 patients who started metformin before or at enrollment, 1226 patients who initiated metformin after enrollment, and an unexposed group of 1392 patients who never used metformin. MAIN MEASURES: Metformin users were categorized into 11 groups in terms of length of time between metformin initiation and enrollment. The percent changes in immortal person-time were calculated for each group.
resultsAs the groups of current metformin users (n = 3485) were added sequentially to the metformin group with potential immortal time bias (n = 1226), the proportion of immortal person-time decreased gradually by 74%. As the immortal time decreased, the association between metformin and cancer risk remained statistically significant (uncorrected hazard ratio 0.54, 95% confidence interval 0.42-0.69, P < 0.0001).
conclusionThe change in the association between metformin and cancer is small compared with the changes in the proportion of immortal time, suggesting that immortal time bias does not account for the observed beneficial effect of metformin on cancer risk. Further studies are warranted to confirm this finding in other cohort studies.
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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 OpenQuestion graph.