Background
Breast cancer (BC) is the cancer with the highest incidence and mortality in women worldwide. Observational epidemiological studies suggest a positive association between testosterone, estradiol, dehydroepiandrosterone sulphate (DHEAS) and both pre- and post-menopausal BC. Since previous studies may be prone to bias and confounding, we used a two-sample Mendelian randomization (MR) analysis to investigate this association.
Methods
Genetic instruments for nine sex steroid hormones and sex hormone binding globulin (SHBG) were obtained from genome-wide association studies (GWAS) conducted in the UK Biobank (total testosterone (TT) N:230,454, bioavailable testosterone (BT) N: 188,507 and SHBG N: 189,473), The United Kingdom Household Longitudinal Study (DHEAS N: 9,722), the LIFE-Adult and LIFE-Heart cohorts (estradiol N: 2,607), the LIFE-Heart cohort only (androstenedione N: 711, aldosterone N: 685, progesterone N: 1,259 and 17-hydroxyprogesterone N: 711) and the CORtisol NETwork (CORNET) consortium (cortisol N: 25,314). GWAS summary statistics were also obtained from the Breast Cancer Association Consortium (BCAC) for overall BC risk (N: 122,977 cases and 105,974 controls) and BC mortality (96,661 BC cases and 7,697 BC-specific deaths). Subtype specific analysis were carried out for incidence of estrogen receptor (ER)+ BC, ER- BC, luminal A-like BC, luminal B-like BC, luminal B/HER2-negative-like BC, HER2-enriched-like BC, triple negative BC (TNBC) and BRCA1 mutated TNBC.
Results
Using an inverse-variance weighted (IVW) approach, we found that a standard deviation (SD) increase in TT, BT and estradiol increased the risk of overall BC (OR: 1.14, 95% CI: 1.09-1.21, OR: 1.19, 95% CI: 1.07-1.33 and OR: 1.03, 95% CI: 1.01-1.06, respectively) and ER+ BC (OR: 1.19, 95% CI: 1.12-1.27, OR: 1.25, 95% CI: 1.11-1.40 and OR: 1.06, 95% CI: 1.03-1.09, respectively). A SD increase in DHEAS also increased ER+ BC risk (OR: 1.09, 95% CI: 1.03-1.09). Subtype specific analyses showed similar associations with ER+ expressing subtypes: luminal A-like BC, luminal B-like BC and luminal B/HER2-negative-like BC. A SD increase in cortisol was associated with poor survival after a diagnosis of ER- BC (HR: 2.35, 95% CI: 1.00-5.49).
Discussion/Conclusion
TT, BT, DHEAS and estradiol increase the risk of ER+ type BCs similar to observational studies, but none of these hormone measures are associated with BC survival. We found some evidence that cortisol reduced ER- BC survival. Stronger genetic instruments are required before definitive conclusions can be made about the role of other sex-steroid hormones in breast cancer. Understanding the role of sex steroid hormones in BC risk, particularly subtype-specific risks, highlights the potential importance of attempts to modify and/or monitor hormone levels in order to prevent BC.
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