In a study of 40 women at high risk for breast cancer, six months of treatment with Celebrex lowered levels of estrogen receptors -- a marker of cell reproduction that can signal cancer, says Banu Arun, MD, an associate professor in the department of breast medical oncology at the University of Texas M.D. Anderson Cancer Center in Houston.

"This is a preliminary but exciting finding that has not been reported in human studies before," she says.

The development of breast cancer is a multistep process, Arun tells WebMD. Even before there is formation of breast cancer cells, regular breast cells start to reproduce while simultaneously accumulating abnormal proteins.

Celebrex appears to disrupt the process at this early step, she says, thus making it an ideal candidate for prevention.

Currently, tamoxifen is the only drug approved for the prevention of breast cancer in women at high risk of the disease due to family history, faulty genes, or other factors. But tamoxifen carries a risk of side effects, including uterine cancer.

As a result, cancer doctors have been searching for a safer, better drug, Arun says. And animal and lab studies suggested that Celebrex stalls the formation, growth, and spread of new cancer cells.

A member of a class of drugs known as Cox-2 inhibitors, Celebrex works by targeting the Cox-2 enzyme that plays a major role in arthritis and inflammation. Celebrex is also used to prevent precancerous growths in people with a rare form of inherited colon cancer, familial adenomatous polyposis. And previous studies have shown that Celebrex may also help fight prostate cancer