Researchers found that among patients with the mutations, those who regularly took aspirin lived longer than those who didn't. Aspirin seemed to make no difference in patients who did not have the mutations.
About one-sixth of all colon cancer patients have the mutated gene and might be helped by aspirin.
Doctors say the findings must be confirmed before aspirin can be recommended for treating the disease, but earlier research also suggests it may help fight cancer.
The study is in this week's New England Journal of Medicine.