This summary table contains detailed information about research studies. Summary tables offer an informative look at the science behind many breast cancer guidelines and recommendations. However, they should be viewed with some caution. In order to read and interpret research tables successfully, it is important to understand some key concepts. Learn how to read a research table.
Introduction: Androgens (such as testosterone) are natural hormones. They are important in sexual development in both men and women.
In women, androgens are produced in small amounts by the ovaries and the adrenal glands. Similar to higher blood estrogen levels, higher amounts of androgens in the blood may be linked to an increased risk of breast cancer in women.
Of the androgens, testosterone has been the most studied in relation to breast cancer risk.
Studies show higher blood levels of testosterone may increase the risk of breast cancer in postmenopausal women.
Most of the studies below excluded women who were taking menopausal hormone therapy (MHT) at the time of the blood collection.
Certain types of MHT might mask the full effect natural blood testosterone levels have on breast cancer risk. By looking only at women who don't take (or who have never taken) MHT, researchers may see more clearly how blood androgen levels affect breast cancer risk.
A pooled analysis of data from 5 studies found higher levels of blood testosterone increased breast cancer risk in premenopausal women .
Learn more about blood androgen 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: Nested case-control studies, case-control studies and pooled analyses with at least 100 breast cancer cases. Table note: Odds ratios above 1 indicate increased risk. Odds ratios below 1 indicate decreased risk.
Risks related to total testosterone levels (unless noted) are shown in this table. Although free testosterone and/or bioavailable testosterone may also be related to breast cancer risk, few studies have measured these, so data are limited at this time.
Study Population(number of participants)
Risk of Breast Cancer in Women with Higher Testosterone LevelsCompared to Women with Lower Testosterone LevelsOdds Ratio (95% CI)
Nested case-control studies
Nurses' Health Study 
EPIC cohort [3-4]
Women’s Health Initiative Observational Study 
Estrogen receptor-positive cancers: 1.55 (0.92-2.61)†
Estrogen receptor-negative cancers: 0.51 (0.28-0.94)†
NYU Women’s Health Study [6-7]
Nurses' Health Study II 
UK Collaborative Trial of Ovarian Cancer Screening 
Melbourne Collaborative Cohort Study 
Manjer et al. 
ORDET cohort [12-13]
Wang et al. 
Yu et al. 
Sturgeon et al. 
* Relative risk for hormone receptor-positive breast cancers was 1.8 (1.3-2.5). Relative risk for hormone receptor-negative breast cancers was 0.6 (0.3-1.2).
† Results are for blood levels of bioavailable testosterone.
‡ Results are for estradiol blood levels measured in the luteal phase of the menstrual cycle.
§ Results are for testosterone blood levels measured in the luteal phase of the menstrual cycle. For testosterone blood levels as measured in the early follicular stage, the risk was also not significant, RR=0.45 (0.17-1.19).
¶ Results for highest vs. lowest blood testosterone levels. Results for a doubling of testosterone levels were statistically significant, RR=1.18 (1.03-1.35).
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