Low-Dose Aspirin for Lynch Syndrome: Lancet | July 2026

Introduction:

Aspirin is one of the few interventions proven to reduce colorectal and other Lynch syndrome–associated cancers. The earlier CaPP2 trial established 600 mg daily aspirin as an effective chemopreventive strategy, but concerns regarding long-term toxicity and bleeding have limited its widespread use. The CaPP3 trial evaluated whether lower aspirin doses could provide comparable cancer protection with improved safety.

Why was this study needed?:

. The optimal aspirin dose for cancer prevention in Lynch syndrome remains uncertain.

. High-dose aspirin is associated with increased gastrointestinal toxicity and bleeding.

. Lower doses may improve long-term adherence if efficacy is maintained.

. Robust randomized evidence comparing different aspirin doses was lacking.

Results:

In this multicenter randomized trial involving nearly 1,900 individuals with Lynch syndrome, the 100 mg aspirin dose demonstrated cancer prevention outcomes broadly comparable to the 600 mg dose in the intention-to-treat analysis, although formal non-inferiority criteria were not fully met across all predefined analyses. The 300 mg dose did not demonstrate non-inferiority. Importantly, adverse events increased with higher aspirin doses, and serious bleeding events were least frequent with the 100 mg regimen. Overall, the lower-dose strategy appeared to retain much of the chemopreventive benefit while offering a more favorable safety profile.

Clinical Impact:

These findings support a shift toward lower-dose aspirin for cancer prevention in individuals with Lynch syndrome. Although the statistical threshold for non-inferiority was not formally achieved, the similar cancer outcomes and substantially lower bleeding risk with 100 mg daily make it an attractive option for long-term chemoprevention. Ongoing follow-up will clarify whether these findings remain consistent over a longer duration.

Bottom Line:

Low-dose (100 mg) aspirin demonstrated cancer prevention outcomes comparable to high-dose aspirin with fewer bleeding complications, supporting its consideration as the preferred long-term chemopreventive strategy for patients with Lynch syndrome while awaiting longer-term follow-up.