Washington, March 6 : Researchers at the University of California, San Diego, have shown that breast cancer recurrence post treatment is associated with high levels of estrogen in the blood.
The team found that women whose breast cancer came back after treatment had almost twice as much estrogen in their blood as compared to women who remained cancer-free.
According to the researchers, their findings suggest that high levels of estrogen lead to an increased risk of cancer recurrence, just as they contribute to the initial development of breast cancer.
"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," study's lead author, Cheryl L. Rock, Ph.D., a professor in the Department of Family and Preventive Medicine at the University of California, San Diego, said.
"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," she added.
Rock said that the results imply that women who have already been treated for breast cancer should do as much as they can to reduce estrogen in their blood, such as exercising frequently and keeping weight down.
"Taking anti-estrogen drugs like tamoxifen may not completely wipe out the hormone's effect in women who have high levels of estrogen," she said.
For the study, the team recruited participants from the larger Women's Healthy Eating and Living Study (WHEL), a dietary intervention trial that followed 3,088 women who had been treated for early stage breast cancer but who were cancer-free at the time they enrolled.
In the current nested case-control study, 153 WHEL participants whose cancer had recurred were matched with 153 participants who remained cancer-free. These pairs were similar in terms of tumour type, body size, age, ethnicity, use of chemotherapy and other variables. Two-thirds of the participants were using tamoxifen, Rock said.
When they enrolled, researchers tested the women's blood for concentrations of the steroid hormones estradiol (the primary human estrogen) and testosterone. They analyzed different forms of estradiol and testosterone in the blood, such as how much was bound to transport proteins (such as to the sex hormone binding globulin, or SHBG) and how much was "free" circulating and able to enter a cell.
Researchers found that higher estradiol concentrations, in all forms, considerably predicted cancer recurrence. Overall, women whose cancer came back had an average total estradiol concentration that was more than double the average for women who remained cancer-free.
Increased levels of testosterone or SHBG levels were not associated with recurrence, contradicting the findings of several previous studies.
Although genetic and metabolic factors likely influence the relationship between circulating sex hormones and risk of breast cancer recurrence, Rock said the study provides solid evidence that higher concentrations of estradiol in the blood contribute to risk for breast cancer recurrence.
The study is published in the March issue of Cancer Epidemiology, Biomarkers and Prevention, a journal of the American Association for Cancer Research.