According to the results of a study published in the Journal of the National Cancer Institute, circulating levels of estrogen and testosterone during specific points in the menstrual cycle appear to influence breast cancer risk in premenopausal women.
Many breast cancers are hormone responsive, prompting interest in the relationship between serum levels of hormones such as estrogen and the risk of breast cancer.
While higher levels of circulating estrogens have been linked with an increased risk of breast cancer in postmenopausal women, less is known about the relationship between circulating hormone levels and breast cancer risk in premenopausal women. Studying the link between hormone levels and breast cancer risk can be challenging in premenopausal women because the levels of many hormones fluctuate over the course of the menstrual cycle.
To explore the link premenopausal breast cancer and levels of circulating hormones, researchers evaluated information from the Nurses’ Health Study II. This study enrolled more then 100,000 female nurses who were between the ages of 25 and 42 when the study began in 1989.
Blood samples were collected from more than 18,000 premenopausal study participants. Women were asked to provide two blood samples-one collected during the early (follicular) phase of their menstrual cycle, and one during the later (luteal) phase of their menstrual cycle. The follicular phase of the menstrual cycle starts with the first day of menstrual bleeding, and the luteal phase of the menstrual cycle starts after ovulation.
Among the women who provided blood samples, 197 were diagnosed with breast cancer during follow-up. Hormone levels in the women with breast cancer were compared to hormone levels in a sample of 394 women without breast cancer. The study assessed levels of estrogens (estradiol and estrone); androgens (testosterone and androstenedione); progesterone; and sex hormone-binding globulin.
- Compared to women with the lowest follicular estradiol levels, women with the highest follicular estradiol levels were roughly twice as likely to develop breast cancer. Luteal estradiol levels were not linked with breast cancer risk.
- Over a three-year period, 50 cases of breast cancer developed among women with the highest follicular estradiol levels compared to 30 cases among women with lowest follicular estradiol levels.
- Women with the highest luteal testosterone or androstenedione levels had a more than two-fold increased risk of estrogen receptor-positive and progesterone receptor-positive (ER+/PR+) breast cancer.
- Levels of estrone, progesterone, and sex hormone-binding globulin did not influence breast cancer risk.
The researchers conclude that levels of circulating estrogens and androgens may influence the development of breast cancer in premenopausal women.
Reference: Eliassen AH, Missmer SA, Tworoger SS et al. Endogenous Steroid Hormone Concentrations and Risk of Breast Cancer among Premenopausal Women. Journal of the National Cancer Institute. 2006;98:1406-15.
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