WEDNESDAY, April 17, 2002 (HealthDayNews) -- Women who have relatively high levels of natural estrogen after menopause are twice as likely to develop breast cancer.
The same may hold true for those with high levels of other sex hormones, including androgens such as testosterone.
That's the sobering news reported in today's Journal of the National Cancer Institute by the International Endogenous Hormones and Breast Cancer Collaborative Group. The group is a panel of physicians and researchers who analyzed data from nine previous breast cancer studies involving some 2,400 women from the United States, Italy, Japan and England.
"There were a number of smaller studies indicating that post-menopausal women with higher estrogen levels were at greater risk for breast cancer. But this analysis pooled all the data from all the studies to demonstrate the increased risk in a fairly large group," says study co-author Joanne F. Dorgan, a researcher at Fox Chase Cancer Center in Philadelphia who was an epidemiologist with the National Cancer Institute when the study was conducted.
It's also the first study to find that testosterone and DHEA are also linked to increased risk of breast cancer, regardless of estrogen levels. DHEA is a hormone that can be converted by the body into estrogen, testosterone, or both.
Breast cancer expert Dr. Clifford Hudis says he's not surprised by the findings, but cautions scientists still don't know the precise role hormones play in breast cancer.
"We still don't know if estrogen is a precipitating factor, causing the cancer to develop, or an exacerbating factor that simply causes a tumor that is already there to grow more rapidly. This study, as good as it is, doesn't answer this question," says Hudis, chief of the Breast Cancer Medical Service at Memorial Sloan-Kettering Cancer Center in New York City.
Indeed, it's possible that estrogen, as well as testosterone, could be indications of other causes that are the true link to the cancer -- including body fat, which has already been cited in numerous studies as a risk factor for breast cancer.
Perhaps not coincidentally, once ovaries stop functioning, as they do after menopause, much of a woman's estrogen supply comes from fat cells -- something Dorgan says her group plans to examine more closely in a subsequent analysis of the data.
In the current study, researchers relied on blood samples taken from each of the women, who ranged in age from 58 to 71. As part of each original study, the samples were tested for levels of sex hormones, including several forms of estrogen, as well as testosterone, DHEA and non-sex hormone binding globulin, a protein that binds to estrogen.
After the blood tests, the women's health profiles were followed for anywhere from two to 12 years.
All totaled, 663 women developed breast cancer. To discover what, if any, role hormones might have played, Dorgan's team compared the results of the women's blood hormone levels to those of the 1,765 cancer-free women in the study.
The result: "Those who had the highest blood levels of sex hormones were at greatest risk for breast cancer -- up to twice the risk of women with lower levels," Dorgan says. Additionally, the higher the estrogen levels, the greater the risk of breast cancer.
Women with the highest levels of non-sex hormone binding globulin also had the lowest risk of breast cancer -- ostensibly because when this compound binds to estrogen it keeps some of the estrogen from reaching breast tissue.
Dorgan adds the link between hormone levels and disease rates was no different for women who developed breast cancer shortly after having their blood tested than it was for those who developed cancer many years later.
"This tells us that high hormone levels were not a pre-clinical indication of breast cancer already at work," Dorgan says.
In addition to the increased breast cancer risk posed by high estrogen levels, Hudis and Dorgan are concerned the cancer was more prevalent in women with high levels of DHEA and testosterone, which is converted to estrogen in breast tissue.
"I think women need to consider the possibility that testosterone therapy, which is increasingly being used for sexual dysfunction in post-menopausal women, may increase their risk of breast cancer," Dorgan says.
The same advice applies to women using hormone replacement therapy (HRT), as well as those using DHEA supplementation, Hudis says.
"I think you have to make educated decisions, and weigh your risks and your benefits when deciding on any hormone therapy," he says.
What To Do: For more information on links between estrogen and breast cancer, visit The Cornell University Program on Breast Cancer. To learn more about breast cancer, check The National Library of Medicine.
