August 12 (HealthDay News) -- The risk of relapse can linger for some breast cancer survivors even after completing five years of what doctors call systemic therapy, a new study found.

But, as gloomy as that news sounds, there is a relative bright spot: the risk may not be as dire as many women fear.

"I would like to think these numbers are smaller than women think they are," the study's lead author, Dr. Abenaa Brewster, a medical oncologist at the University of Texas M.D. Anderson Cancer Center in Houston, said.

Most women, she added, "remain terrified they are going to relapse. I think the message for women is, the risk may not be as large as they think."

Brewster's team evaluated 2,838 breast cancer patients whose disease ranged from stage I to III. All had been treated with some form of adjuvant systemic therapy between 1985 and 2001 and had remained disease-free for five years, which is traditionally considered a landmark in cancer survival.

The women had a variety of treatments -- surgery, chemotherapy, radiotherapy or endocrine therapy. Endocrine therapy involves tamoxifen, aromatase inhibitors and a combination of the drugs and is usually given for five years.

About 10 years after the diagnosis, 89 percent of the women remained recurrence-free. And about 80 percent remained recurrence-free 15 years after the diagnosis.

In all, 216 patients developed a recurrence, Brewster said. She found that the risk or recurrence varied by stage and tumor type. Those women with stage I disease had a 7 percent chance of relapse; stage II, 11 percent; and stage III, 13 percent.

Besides the stage of cancer at diagnosis, hormone receptor status affected risk, the study found. "Women who had ER-positive cancer were more likely to have late recurrences than those with ER-negative," Brewster said. This finding held true for premenopausal and postmenopausal women. While 34 ER-negative women had a relapse, 149 ER-positive did.

"Estrogen receptor status is a tumor marker we look at," Brewster said. "We know that those who have ER-positive tumors [have] cancers that are responsive to the effects of estrogen."

While women in the study were taking a variety of hormone therapies, none took five years of aromatase inhibitors, which are now the standard of care for postmenopausal women but weren't when the study began in 1985, Brewster said.

The study findings were published online Aug. 12 in the Journal of the National Cancer Institute.

Dr. Len Lichtenfeld, deputy chief medical officer for the American Cancer Society, said the study findings leave some unanswered questions, such as the best course of action at the five-year mark. But it offers some interesting information, he added.

"The major message is that even though women may have gone through five years of hormonal therapy, they are still at risk of relapse," he said. Another important finding, he added, is that those women with ER-positive tumors seem to be at higher risk than those with ER-negative tumors.

"Basically the jury is out on the potential value of additional treatment strategies once the five years is completed," Lichtenfeld said. "Based on this study, we need to be open to question whether other treatment programs may be appropriate in some of these women after the five-year period is completed."

SOURCES: Abenaa Brewster, M.D., assistant professor of medicine and medical oncologist, University of Texas M.D. Anderson Cancer Center in Houston; Len Lichtenfeld, M.D., deputy chief medical officer, American Cancer Society, Atlanta; Aug. 12, 2008, Journal of the National Cancer Institute