Taking aspirin does not improve breast cancer patients' outcomes, according to a study that challenges previous research.

Investigators looked at more than 1,000 breast cancer patients and found that aspirin use was associated with worse outcomes and a lower chance of survival, United Press International reported.

"Past studies have found that aspirin may hold anti-cancer benefits. However, many of them were preliminary, preclinical, and didn't support a clear mortality benefit. They also didn't look at prior use of aspirin," study author Dr. Julia Tchou, associate professor of surgery, University of Pennsylvania, said in a news release.

"Our data did not support the notion that this century-old pill has protective qualities and down-the-road benefits for breast cancer patients. However, larger patient cohort studies are needed to confirm our results," she added.

Another study found that aspirin's effect on breast density may help diagnosis breast cancer at an earlier stage, UPI reported.

Both studies were presented at the San Antonio Breast Cancer Symposium.