# 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/), [Polycythaemia vera (PV)](https://onco.cc/cancers/polycythaemia-vera/)
- terms: [Erythromelalgia](https://onco.cc/terms/erythromelalgia/)

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JSON: https://onco.cc/api/v1/entities/aspirin.json