HealthWatch (WFRV) -- For decades, it's been prescribed to help women fight breast cancer from coming back. Now a new study shows staying on the drug longer may not have the effects doctors once believed. Here is a story that could change breast cancer survivors' treatment.

This has been Carol Yancey's routine every morning for four years.

"I had a lumpectomy," Carol Yancey (Breast Cancer Survivor.

Tamoxifen is helping her reduce the risk of breast cancer recurrence. It's normally a five year treatment.

"For the last, oh gosh, couple of decades, I guess, we've been using five years as our standard," said, Dr. C. Kent Osborne, M.D., at the Baylor College of Medicine in Houston, TX.

The belief was the benefit of staying on it longer was outweighed by a woman's risk, of things like uterine cancer and blood clots.

"I think this study goes a long way to show that actually doesn't seem to be the case," Dr. Steven Isakoff, M.D., Ph.D., at the Massachusetts General Hospital Cancer Center in Boston, Mass.

Presented at the recent Breast Cancer Symposium, the Atlas Study involved more than 68 hundred women with E.R. positive Breast cancer, who'd been on Tamoxifen for five years. Some were randomly assigned to stay on the drug for five more years. The results found the women on Tamoxifen for ten years had their risk of recurrence cut by 25 percent. Their risk of dying from breast cancer also went down 29-percent.

"I guess I'm a little bit surprised at the findings," said Dr. Osborne.

But doctors warn extending Tamoxifen isn't right for all patients.

"For someone who has a generally low risk of recurrence, we'll have to weigh the risks and benefits," stated Dr. Isakoff.

Now, the challenge could be spreading the word.

"But I think it will just naturally find its spot in the treatment," explained Dr. Osborne.

If carol's doctor says this will continue to be her daily routine for six more years, instead of one more year.

"I would do it, if it means that this doesn't come back, and I don't have to go through any of that again," stated Yancey.

The Atlas Study found ten years of Tamoxifen does have some side effects, the biggest, being, the risk of endometrial cancer. But because it's generally curable, researchers say that risk is heavily outweighed by the possible benefits of extending the drug treatment.