Evidence Summary

Aspirin has one of the largest repurposing evidence bases in oncology.

That evidence spans epidemiology, mechanism research, tissue studies, and now Phase 3 oncology data in a biomarker-defined colorectal-cancer subgroup. Even so, the benefit is not uniform across all cancer settings.

Research Overview

1. Phase 3 prospective trial data now supports aspirin in a biomarker-defined colorectal-cancer subgroup

2. Long-term observational data links aspirin use with lower incidence of several cancers

3. Mechanistic work supports effects on inflammation, metastasis, immunity, and tumour-suppressor signalling

4. Tissue studies suggest aspirin may reduce nodal spread and improve immune infiltration

5. Broad oncology use remains investigational outside selected subgroups

Clinical Application Status

Approved status: Approved for pain, inflammation, and cardiovascular use, not as an approved cancer drug.

Clinical use: Used experimentally in repurposed-drug and investigational oncology settings.

Evidence strength: Strongest in PIK3CA-mutated colorectal cancer. More limited in other tumour types.

Key Advantages

1. Low cost and wide availability

2. Multi-pathway action across inflammation, platelet biology, immunity, and signalling

3. Long medical history outside oncology

4. Biomarker-guided potential in colorectal cancer

5. Combination interest with chemotherapy and immunotherapy

Key Considerations

1. Bleeding risk is real — especially in older adults and higher-risk patients

2. Age matters — benefit is not universal across all populations

3. Biomarker selection matters — especially PIK3CA status

4. Duration matters — some benefits appear over long-term use

5. It is not standard of care in most oncology settings

Bottom line

Aspirin is no longer just an epidemiological curiosity in oncology. It now has meaningful Phase 3 support in a molecularly defined colorectal-cancer subgroup.

Outside that setting, the evidence remains promising but not yet practice-changing.

Key References

• Elwood P et al. (2021). Aspirin and cancer survival: a systematic review and meta-analyses of 118 observational studies (~20% reduction in cancer mortality across 18 cancer types). ecancer 15:1258. https://doi.org/10.3332/ecancer.2021.1258[^1][^2]

• Cuzick J et al. (2024). Aspirin and cancer treatment: systematic reviews and meta-analyses of evidence for and against. British Journal of Cancer 130:1–15. https://doi.org/10.1038/s41416-023-02506-5[^3][^4]

• Li Y et al. (2025). Effect of aspirin use on cancer incidence and mortality: a meta-analysis. Public Health 248:105924. https://pubmed.ncbi.nlm.nih.gov/40865396/[^5]

• Li K et al. (2025). Long-term use of low-dose aspirin for cancer prevention (population study: 538,147 aspirin users, SHR 0.92 for cancer risk; SHR 0.80 for cancer mortality). Cancer Medicine 14(1). https://pmc.ncbi.nlm.nih.gov/articles/PMC12008822/[^6]

• Drew DA et al. (2021). Evaluation of Aspirin Use With Cancer Incidence and Survival (PLCO trial cohort, 139,896 participants). JAMA Network Open 4(1):e2033622. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2775219[^7]

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