They looked at nearly 1,300 people with colorectal cancer who'd been followed for an average of 12 years. All the patients in the study had surgery for colon cancer and many also had chemotherapy.

Among the 549 participants who used aspirin regularly after their diagnosis, 81 died from colorectal cancer (about 15 percent). In contrast, among the 730 people who didn't use aspirin, 141 died of the disease (about 19 percent).

Taking into account other cancer risk factors, such as family history, the researchers calculated aspirin's overall benefit: a 29 percent reduction in risk of cancer death.

"It's exciting that an inexpensive, commonly used medication may be of benefit among this group of patients who are worried about having their cancer recur," Chan said.

About one-third of the tumors could be tested for Cox-2. Aspirin helped only those patients whose tumors tested positive for the enzyme. That makes sense, Chan said, because aspirin blocks the enzyme, which is thought to play a role in cancer's spread.

If aspirin becomes the standard of care in colon cancer, testing for Cox-2 may become routine, Neugut said. That wouldn't add much to costs, he said, because tumor tissue already is tested and a Cox-2 test could be easily added.