Colorectal and lung cancer patients who were taking low-dose aspirin in the year prior to diagnosis tended to have lower tumor extent and fewer metastatic disease, according to new study results. For these cancers, researchers believe the benefit of aspirin use appears to be during both early and late cancer progression.

In analyzing data from Swedish cancer and prescription drug registries, researchers found 20-40% fewer colon, lung and breast cancer patients who had taken aspirin had tumors that spread to other areas of the body than those who had not taken aspirin.

Tumors on average were smaller and less advanced among aspirin users with colon and lung cancer, but not those with breast or prostate cancer, something the researchers were unable to explain. Senior author Yudi Pawitan, of the department of medical epidemiology and biostatistics at the Karolinska Institutet in Stockholm, Sweden noted the difference might be due to the fact that breast and prostate cancers often have more hormonal factors involved.

Still, the authors noted that their finding doesn’t mean everyone should be taking aspirin to ward off advanced cancer, noting that regular use of aspirin is linked with an increased chance of gastrointestinal bleeds. “Because it has side effects, it would be difficult if not impossible to prescribe aspirin to all people,” said Pawitan.