Chalk up another potential benefit to taking aspirin. A new lab study has found that a daily dose of aspirin was effective at blocking breast tumor growth.

The findings, to be published in the appear in the July issue of the journal Laboratory Investigation, add to previous studies that have found aspirin can help prevent colon, gastrointestinal, prostate, and other cancers.

Lead researcher Sushanta Banerjee, M.D., research director of the Cancer Research Unit at the Kansas City Veterans Affairs Medical Center, said the new findings — based on studies of mice — suggest aspirin appears to block the growth and development of cancer stem cells that can chemotherapy or other cancer treatment. Such residual cells go dormant until conditions in the body are more favorable for them to again reproduce.

"In cancer, when you treat the patient, initially the tumor will hopefully shrink," said Dr. Banerjee. "The problem comes five or 10 years down the road when the disease relapses. When they reappear they can be very aggressive, nasty tumors."

But the VA research found aspirin alters the molecular signature in breast cancer cells enough so that they wouldn't reawaken and spread. Not only did the research show that exposure to aspirin dramatically increased the rate of cell death, it also left the surviving tumor cells unable to grow.

"We found aspirin caused these residual cancer cells to lose their self-renewal properties," said Dr. Banerjee. "Basically, they couldn't grow or reproduce. So there are two parts here. We could give aspirin after chemotherapy to prevent relapse and keep the pressure on, which we saw was effective in both the laboratory and the mouse model, and we could use it preventatively."

Experts suggest patients consult a doctor before starting a daily aspirin regimen because it can thin the blood and increase the risk of gastrointestinal bleeding.

"Of course there is a risk," noted Dr. Banerjee, "But you have to weigh that against the risks of cancer. It's true this is relatively new and we don't know all the side effects yet, but this was a very low dose."