Evidence Explainer · Aspirin, mortality & cancer
ASPREE’s cancer signal changed across longer follow-up
The randomized trial found an unexpected cancer-mortality imbalance. Longer follow-up found no difference in overall cancer incidence and no post-trial mortality legacy effect.
Discovery, counterevidence, claim mapping, identifiers, funding, correction state and prose were reviewed before release.
Evidence at a glance
Randomized-period signal plus observational extension
- Study type
- Randomized trial secondary mortality analysis followed by a trial-derived observational extension
- Studied in
- Humans
- Participants / sample
- 19,114 original ASPREE participants; 14,907 cancer-free randomized-phase survivors in the post-trial legacy analysis
- Publication status
- Peer reviewed; no linked correction, retraction or expression of concern identified as of verification
- Outcome type
- All-cause mortality, cancer incidence and cancer-related mortality
- Evidence maturity
- Unexpected randomized-period secondary signal with median 8.6-year combined follow-up
- Conflicts / funding
- Public and institutional support, Bayer-supplied trial product, and author outside relationships disclosed
- Our assessment
- No overall cancer-incidence association; elevated combined cancer mortality did not persist as a post-trial legacy association
Read this first
Three takeaways
- During median 4.7-year randomized follow-up, all-cause mortality was higher with aspirin; cancer-related death was 3.1% versus 2.3%. Investigators called this unexpected and cautioned interpretation.
- Across median 8.6 years combined follow-up, original aspirin assignment was not associated with overall cancer incidence: HR 0.98, 95% CI 0.92–1.05.
- In the post-trial legacy phase, original assignment was not associated with cancer mortality: HR 1.02, 95% CI 0.83–1.25. Assigned aspirin had already stopped.
Keep time periods separate
Randomization does not keep treatment assigned forever
Randomized period
Aspirin or placebo was assigned; mortality was a secondary outcome and cause-specific work included exploratory analyses.
Combined follow-up
Original groups were followed across trial and later years, even though assigned treatment stopped.
Legacy analysis
Post-trial outcomes were compared by original assignment, not by continued randomized exposure.
Different outcomes
Cancer incidence, cancer mortality and all-cause mortality cannot substitute for one another.
The bottom line
ASPREE found an unexpected randomized-period mortality imbalance driven largely by cancer deaths. The 2026 extension found no overall cancer-incidence association and no post-trial cancer-mortality legacy association, so neither a simple cancer-harm nor cancer-prevention claim is justified.
What researchers did
The 2018 analysis classified deaths during the randomized trial. The 2026 cohort study then linked the original ASPREE groups with observational ASPREE-XT follow-up, reporting both combined long-term outcomes and a post-trial-only legacy analysis.
What they found in the trial
All-cause mortality was 12.7 versus 11.1 per 1,000 person-years; HR 1.14, 95% CI 1.01–1.29. Cancer-related death was 3.1% versus 2.3%; HR 1.31, 95% CI 1.10–1.56.
What longer follow-up found
Across median 8.6 years, overall cancer incidence HR was 0.98 (95% CI 0.92–1.05) and cancer mortality HR was 1.15 (1.03–1.29). In post-trial-only analyses, incidence HR was 0.91 (0.82–1.01) and mortality HR 1.02 (0.83–1.25).
How strong is the evidence?
The randomized-period comparison is strong for assigned treatment but mortality was secondary and the cancer pattern unexpected. Combined follow-up preserves original group comparison while adding untreated years; the post-trial phase cannot be read as continued randomized dosing.
What this does not show
The studies do not establish that aspirin broadly causes cancer, prevents cancer, or changes lifespan for every older adult. Cancer incidence is not cancer mortality, and a post-trial null legacy association does not erase the randomized-period signal.
Safety, funding and conflicts
Aspirin’s bleeding risk remains relevant even in a cancer-focused article. ASPREE had public and institutional support; Bayer supplied study product. The 2026 paper lists public grants and several authors’ outside pharmaceutical or board relationships.
Educational boundary
This is not advice to start, continue or stop aspirin for cardiovascular or cancer prevention. Individual decisions require clinical assessment of indication, prior disease, bleeding risk, other medicines and current guidance.
Primary sources
Sources, roles and limits
- ASPREE all-cause mortality analysis
- Identifier
- PMID:30221595 · PMCID:PMC6433466 · DOI:10.1056/NEJMoa1803955 · NCT01038583
- Role
- Randomized-period all-cause and cause-specific mortality support
- Limitation
- Mortality was secondary; specific cause analyses were exploratory and the signal was unexpected.
- ASPREE-XT cancer incidence and mortality follow-up
- Identifier
- PMID:41609798 · DOI:10.1001/jamaoncol.2025.6196
- Role
- Combined and post-trial follow-up support
- Limitation
- Later years followed original groups after assigned treatment stopped.
- ASPREE registry
- Identifier
- NCT01038583
- Role
- Original trial identity and design
- Limitation
- Does not convert observational extension years into randomized exposure.
- ASPREE statistical analysis plan
- Identifier
- PMID:29111960 · DOI:10.1177/1747493017741383
- Role
- Prespecified trial-analysis context
- Limitation
- Does not pre-specify every later extension analysis.
- FDA aspirin facts
- Identifier
- FDA page checked August 3, 2026
- Role
- Current bleeding and medication-decision context
- Limitation
- General safety information is not a cancer-outcome study.
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Disclosures and history
- August 3, 2026 — source discovery and independent verification completed before prose drafting.
- August 3, 2026 — randomized, combined-follow-up, post-trial, incidence, mortality, funding and safety boundaries reviewed.
- Corrections: no linked correction, retraction or expression of concern identified for the featured records as of verification; follow-up and regulator records must be rechecked when this story is updated.