Table 6: Blood estrogen levels and the risk of breast cancer

Introduction: Estrogens are natural hormones produced mainly in the ovaries in premenopausal women, and mainly in fat tissue in postmenopausal women. They are important in sexual development and other body functions.   

Blood estrogen levels, breast cancer risk and menopausal status

Higher levels of estrogen in the blood are linked to an increased risk of breast cancer in postmenopausal women. Researchers are studying a possible link to breast cancer in premenopausal women as well.

Because of the different sources (and different levels) of estrogen in premenopausal and postmenopausal women, it is important to look at studies of estrogen and breast cancer risk by menopausal status.  

Blood estrogen levels and breast cancer risk in postmenopausal women

The studies listed in the table below show higher blood levels of the estrogen called estradiol increase the risk of breast cancer in postmenopausal women.

Blood estrogen and postmenopausal hormones

All of the studies below excluded women who were using postmenopausal hormones at the time of blood collection. Certain postmenopausal hormones might mask the full effect natural blood estrogen levels have on breast cancer risk. By looking only at women who are not taking (or who have never taken) postmenopausal hormones, researchers may see more clearly how blood estrogen levels affect breast cancer risk.  

Blood estrogen levels and breast cancer risk in premenopausal women

Few studies have looked at blood estrogen levels and breast cancer risk in premenopausal women. In the only two large studies to date, findings were mixed.

Studies in premenopausal women are challenging because estrogen levels vary over the menstrual cycle. Estrogen levels are much lower in the early phase (follicular) than the late phase (luteal) of the menstrual cycle.

Learn more about blood estrogen levels and breast cancer risk.

Learn about the strengths and weaknesses of different types of studies.

See how this risk factor compares with other risk factors for breast cancer.

Study selection criteria: Prospective nested case-control studies with at least 75 breast cancer cases, pooled analyses and meta-analyses.

Table note: Relative risks above 1 indicate increased risk. Relative risks below 1 indicate decreased risk.

Risks related to total estradiol levels are shown in this table.  

* Relative risk for estrogen receptor-positive and progesterone receptor-positive (ER+/PR+) breast cancers was 2.8 (2.0-4.0). Relative risk for estrogen and progesterone receptor-negative (ER-/PR-) breast cancers was 1.1 (0.6-2.1).

† Relative risk for ER+ cancers only. Relative risk for ER- breast cancers was 1.65 (0.91-2.98).

‡ High versus low levels of follicular estradiol in women at the same point in their menstrual cycle. Results for luteal estradiol levels were not statistically significant.

§ Relative risk for women with higher levels of free estradiol compared to women with lower levels of free estradiol was 1.75 (1.06-2.89).

|| Relative risk for ER+ cancers only. Authors noted an increase in risk before adjustment for blood testosterone levels.

References  

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Updated 03/12/13