Now, a new study shows, staying on the drug longer may not have the effects doctors once believed.
Tamoxifen is helping Carol Yancey reduce the risk of breast cancer recurrence. It's normally a five-year treatment.
"I had a lumpectomy," said Yancey.
"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., Baylor College of Medicine.
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," said Steven Isakoff, MD, Ph.D, Massachusetts General Hospital Cancer Center.
Presented at the recent Breast Cancer Symposium, The Atlas Study involved more than 6,800 women with ER-positive breast cancer who had 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 10 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," said Dr. Isakoff.
Now, the challenge could be spreading the word.
"But I think it will just naturally find its spot in the treatment," said Dr. Osborne.
If Yancey'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," said Yancey.
The Atlas Study found 10 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.
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