Cohort studyindependent cross-checkabstract checked★ key study I-INS-125 in-depth review
Glargine and breast cancer in older US women
Similar Breast Cancer Risk in Women Older Than 65 Years Initiating Glargine, Detemir, and NPH Insulins.
Overview
Bradley MC et al.. Diabetes Care 2020 · PMID 32075848 · DOI 10.2337/dc19-0614
Among more than 300,000 women starting insulin, glargine users did not have more breast cancer, even with longer use or higher doses.
Does the study support the specific claim? No · Methodological quality: high
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Compare breast cancer by insulin type.
- How was the study done?
Medicare new-user cohort.
- How many people, animals or samples were studied?
317,559 women >=65.
- What was actually found?
HR 0.97 vs NPH; no dose or duration effect.
- How large was the observed effect?
HR 0.97 (0.88-1.06).
- What do the results mean in everyday life?
Glargine does not appear to raise breast cancer risk.
- What are the study's limitations?
Older women only.
- What does it say about Elawady's specific claim?
Contradicts dose-dependent cancer claim.
- Do the results apply to Germany and Europe?
Applicable.
- What can explicitly not be concluded from this study?
Cannot exclude small effects in younger women.
Scientific in-depth review
1. Full reference
- Authors
- Bradley MC et al.
- Journal
- Diabetes Care
- Year
- 2020
- Identifier
- PMID 32075848 DOI 10.2337/dc19-0614
- Verification
- verified – PubMed efetch 2026-10-26; Crossref 2026-10-26
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
US government (FDA) support (record).
2. Research question
Is glargine initiation associated with breast cancer compared with NPH or detemir?
3. Study design and population
- Study design
- Cohort study – Retrospective new-user cohort (US Medicare)
- Population
Female Medicare beneficiaries >=65 initiating insulin
- Country
USA
- Period
2006-2015, follow-up to 2017
- Sample size
317,559 (glargine 203,159; detemir 67,012; NPH 47,388)
- Inclusion and exclusion criteria
New users
4. Methods and endpoints
- Exposure / intervention
Glargine
- Comparator
NPH; detemir
- Endpoints
Incident breast cancer
- Statistical methods
Weighted Cox models by duration, dose, follow-up
5. Actual results
- Results
Glargine vs NPH HR 0.97 (0.88-1.06); vs detemir 0.98 (0.92-1.05); no increase by duration, follow-up length or cumulative dose; no dose-response.
- Absolute risks
not reported
- Authors' conclusion
Glargine use was not associated with increased breast cancer risk.
6. Strengths
- Very large
- New-user design
- Dose and duration analyses
7. Weaknesses
- Older women only
- Claims data
8. Risk of bias
- Orienting tool
- ROBINS-E
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- low
- Rationale
New-user active-comparator design reduces biases.
9. Assessment of the statistical interpretation
Precise null.
10. Relevance to the specific claim
Large new-user study finding no dose- or duration-dependent breast cancer risk with glargine.
11. Independent contrary findings
12. Transferability to Germany and Europe
Directly applicable; same biology and clinical standards in Europe.
13. Overall methodological judgement
Strong counter-evidence to the breast cancer and dose claims.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | high |
| Risk of bias | low |
| Precision of results | high |
| Directness | direct |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | mixed |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
15. Linked fact checks
- Insulin glargine increases cancer risk in a dose-dependent way (and long-term use increases breast cancer). – Studies contradicting or limiting the claim