These findings are published the October 21,2011 issue of Breast Cancer Research.
The researchers looked at eight different hormones in women and compared these with risk of breast cancer in post-menopausal women. “We found that for each additional elevated hormone level, the risk of breast cancer increased by 16 percent,” said lead study author Shelley Tworoger, PhD, an associate epidemiologist at BWH and an assistant professor of Medicine at Harvard Medical School.
The highest levels of circulating estrogens (estrone, estradiol, and estrone sulfate), prolactin, and androgens (testosterone, androstenedione, DHEA, and DHEA-sulfate) were individually associated with between 50 percent to two-fold increase in relative breast cancer risk. The number of different hormones elevated above normal further increased risk, so that women with one elevated hormone had an increased risk of 10 percent, compared to women with no elevated hormones, but the risk for women with five or six elevated hormone levels was doubled, and that for women with seven or eight was tripled.
The measured risks were also slightly higher for women that were estrogen-receptor-positive (ER-positive), in which the women with cancer have estrogen receptors present on many of the cancer cells. “This suggests that ER-positive tumors are particularly sensitive to the influences of these hormones,” said Dr. Tworoger.
Researchers used blood samples collected from nurses up to nine years before health information, including their breast cancer status, was recorded. Post-menopausal women who were diagnosed with breast cancer were matched to two controls of a similar age.
“Elevated estrogens had the biggest effect on risk, however, androgens, and prolactin also contribute to increasing risk of breast cancer. These hormones are known to stimulate the growth of breast cancer cells in the lab and, while androgens can be converted to estrogen in the body, these hormones have also been found to stimulate cancer cell growth,” explained Dr. Tworoger. “Our results suggest that models used to assess breast cancer risk could be improved by taking into account multiple sex hormone and growth hormone levels.”
The researchers concluded that gathering additional information about why some women have low (or high) levels of multiple hormones and the interplay between hormones in influencing breast cancer risk has the potential to improve risk assessment and prevention recommendations.