# Aspirin

Source: https://onco.cc/drugs/aspirin/  
OnCo record `aspirin` (Treatment). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Aspirin is not a cancer drug but sits in cancer care in two places: low doses prevent clots in polycythaemia vera and essential thrombocythaemia, and long-term use lowers colorectal cancer in people with Lynch syndrome, while a trial in the healthy elderly found no benefit and possible harm.

## Summary

In the myeloproliferative neoplasms, low-dose aspirin is given to almost everyone with polycythaemia vera and to low-risk and high-risk essential thrombocythaemia, because activated platelets cause both the microvascular symptoms (erythromelalgia, headache) and the arterial clots that drive mortality; the ECLAP trial in polycythaemia vera showed fewer combined cardiovascular events with aspirin. In prevention, the CAPP2 trial in Lynch syndrome found that 600 mg of aspirin a day for at least two years roughly halved colorectal cancers over the following decade, and long-term follow-up of cardiovascular trials suggested fewer colorectal cancer deaths. Against that, ASPREE, a trial in healthy adults over 70, found more cancer deaths on aspirin than placebo, so aspirin is not recommended for cancer prevention in older people without a specific indication. The Add-Aspirin trial is testing aspirin after treatment for breast, colorectal, gastro-oesophageal and prostate cancer. Its harms are bleeding, especially in the gut, and it must be avoided in essential thrombocythaemia with acquired von Willebrand deficiency.

## Fields

- Kind: Treatment
- Status: established
- Last checked: 2026-09-16
- Also known as: Acetylsalicylic acid; Low-dose aspirin
- Tags: mpn; prevention
- Modality: Antiplatelet and anti-inflammatory small molecule (cyclo-oxygenase inhibitor), used in cancer for thrombosis prevention and studied for chemoprevention
- Mechanism: Irreversibly blocks cyclo-oxygenase 1 in platelets, stopping thromboxane production and platelet clumping; at higher doses also blocks cyclo-oxygenase 2 and prostaglandin-driven inflammation, the proposed route to its effect on colorectal cancer.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Aspirin
- CAPP2 long-term follow-up, Lancet 2020: https://doi.org/10.1016/S0140-6736(20)30366-4
- ASPREE cancer outcomes, JNCI 2021: https://doi.org/10.1093/jnci/djaa114
- Add-Aspirin trial: https://www.addaspirintrial.org/

## Connected records

- cancers: [Colorectal cancer](https://onco.cc/cancers/colorectal/), [Essential thrombocythaemia (ET)](https://onco.cc/cancers/essential-thrombocythaemia/), [Mismatch-repair deficient (MSI-high) colorectal cancer](https://onco.cc/cancers/msi-high-colorectal/), [Polycythaemia vera (PV)](https://onco.cc/cancers/polycythaemia-vera/), [Primary myelofibrosis](https://onco.cc/cancers/primary-myelofibrosis/)
- key papers: [CAPP2: two years of aspirin cuts bowel cancer in Lynch syndrome by more than a third over 10 years](https://onco.cc/key-papers/paper-capp2-aspirin-lynch-lancet-2020/), [Effect of Aspirin on Cancer Incidence and Mortality in Older Adults](https://onco.cc/key-papers/paper-mcneil-j-natl-cancer-inst/)
- trials: [A Phase IIa Randomized, Double-Blinded Clinical Trial of Naproxen or Aspirin for Cancer Immune Interception in Lynch Syndrome](https://onco.cc/trials/nct05411718/), [A Trial of Aspirin on Recurrence and Survival in Colon Cancer Patients](https://onco.cc/trials/nct02301286/), [Add-Aspirin](https://onco.cc/trials/add-aspirin/), [ALASCCA](https://onco.cc/trials/alascca/), [Aspirin in Colorectal Cancer Liver Metastases](https://onco.cc/trials/nct03326791/), [ASPIRIN Trial Belgium](https://onco.cc/trials/nct03464305/), [ASPREE (ASPirin in Reducing Events in the Elderly)](https://onco.cc/trials/aspree/), [Assessment of Direct Biomarkers of Aspirin Action to Develop a Precision Chemoprevention Therapy of Colorectal Cancer](https://onco.cc/trials/nct03957902/), [CAPP2](https://onco.cc/trials/capp2/), [Combination Immunotherapy Treatment for Locally Advanced Unresectable or Metastatic, PD-L1 Negative (CPS<10), gBRCA Negative, Triple Negative Breast Cancer Incl](https://onco.cc/trials/nct07762703/), [Dexamethasone, Aspirin, and Diethylstilbestrol in Treating Patients With Locally Advanced or Metastatic Prostate Cancer](https://onco.cc/trials/nct00316927/), [Finding the Best Dose of Aspirin to Prevent Lynch Syndrome Cancers](https://onco.cc/trials/nct02497820/), [Hormone Therapy With or Without Docetaxel And Estramustine in Treating Patients With Prostate Cancer That is Locally Advanced or At High Risk of Relapse](https://onco.cc/trials/nct00055731/), [Perioperative Platelet Inhibition With Acetylsalicylic Acid in Patients With Resectable Tumors of the Pancreatic Head](https://onco.cc/trials/nct05637567/), [PT-1 (Primary Thrombocythaemia 1)](https://onco.cc/trials/pt-1/), [Regorafenib With Low-dose Chemotherapies and Aspirin Followed by Standard Chemotherapies in Metastatic Colorectal Cancer](https://onco.cc/trials/nct05462613/)
- people: [John Burn](https://onco.cc/people/john-burn/)
- terms: [Erythromelalgia](https://onco.cc/terms/erythromelalgia/), [IPSET-thrombosis score (essential thrombocythaemia)](https://onco.cc/terms/ipset-thrombosis/), [Microenvironment and inflammation: tumours as wounds that do not heal](https://onco.cc/terms/microenvironment-inflammation-theory/)

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