Surprise findings from a landmark trial suggest that aspirin might accelerate the rate of progression of advanced malignancies in elderly people, researchers say.

The team conducted a post-hoc analysis of data from the ASPirin in Reducing Events in the Elderly (ASPREE) trial in which more than 19,000 people aged over 70 in Australia and the US were randomised to 100mg enteric-coated aspirin daily or placebo.

No significant difference was found between the trial arms for incidence of cancer overall, or for haematological or solid cancers, reported Professor John McNeil, of the Walter and Eliza Hall Institute of Medical Research in Melbourne, and colleagues.

But the risk of incident cancer that had already metastasised was 19% higher in the aspirin arm and the risk of a cancer being diagnosed at stage 4 was 22% higher, the investigators wrote in the Journal of the National Cancer Institute.