# 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

<br>

* 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\[^1\]\[^2\]](https://doi.org/10.3332/ecancer.2021.1258\[%5E1]\[%5E2])
* 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\[^3\]\[^4\]](https://doi.org/10.1038/s41416-023-02506-5\[%5E3]\[%5E4])
* 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/\[^5\]](https://pubmed.ncbi.nlm.nih.gov/40865396/\[%5E5])
* 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/\[^6\]](https://pmc.ncbi.nlm.nih.gov/articles/PMC12008822/\[%5E6])
* 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\[^7\]](https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2775219\[%5E7])

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