(Ivanhoe Newswire) -- The higher a woman’s estrogen level, the more likely breast cancer will come back, according to new research. The new study reveals that women whose breast cancer came back had almost twice as much estrogen in their blood than women who remained cancer-free.

“While this makes sense, there have been only a few small studies that have looked at the link between sex hormones in the blood and cancer recurrence,” says Cheryl Rock, Ph.D., a professor in the Department of Family and Preventive Medicine at the University of California, San Diego. “This is the largest study to date and the only one to have included women taking agents such as tamoxifen to reduce estrogen’s effect on cancer growth.”
 

For the study, researchers used data from a larger study on dietary intervention for breast cancer. Study authors matched 153 participants whose cancer had recurred to 153 participants who remained cancer-free. The pairs were alike in terms of tumor type, body size, age, ethnicity and treatments used. All of these participants had their blood tested at the beginning of the study, when they were all cancer-free. Two-thirds of the participants were using tamoxifen.

Researchers report higher levels of estradiol concentrations significantly predicted cancer recurrence. Estradiol is a steroid hormone and the primary human estrogen. Women whose cancer returned has more than double the amount of estradiol compared to women who remained cancer-free.

“What the results mean for women who have already been treated for breast cancer is that they should do as much as they can to reduce estrogen in their blood, such as exercising frequently and keeping weight down,” Dr. Rock said. “Taking anti-estrogen drugs like tamoxifen may not completely wipe out the hormone’s effect in women who have high levels of estrogen.”

SOURCE: Cancer Epidemiology, Biomarkers and Prevention, March 2008