Depression, Antidepressant Use, and Postmenopausal Breast Cancer Risk.
BACKGROUND
Whether depression and antidepressant (AD) use might influence breast cancer risk is unclear, and these exposures have not been evaluated together in a single, prospective cohort study of breast cancer risk.


METHODS
Among 71,439 postmenopausal women in the Women's Health Initiative Observational Study (WHI-OS), we estimated multivariable-adjusted HRs for the independent and joint effects of depressive symptoms and AD use on breast cancer risk using Cox proportional hazards regression.


RESULTS
When analyzed separately, neither depressive symptoms nor AD use at baseline were associated with a significantly increased risk of total breast cancer (HR = 0.96, 95% CI, 0.85-1.08; HR = 1.04, 95% CI, 0.92-1.20, respectively) or invasive breast cancer (HR = 0.98, 95% CI, 0.86-1.12; HR = 1.00, 95% CI, 0.86-1.16, respectively). Current AD use was associated with a borderline-significant increase of in situ breast cancer (HR = 1.30, 95% CI, 0.99-1.75) after adjustment for depressive symptoms; however, this relationship was attenuated after adjustment for mammographic screening (HR = 1.08, 95% CI, 0.76-1.51). No significant variation in total breast cancer risk was observed when the separate and joint effects of depressive symptoms and AD use were explored (P for interaction = 0.14).


CONCLUSION
We found no evidence that either depression or AD use influences breast cancer risk. An elevated risk of in situ disease among AD users could not be ruled out, though is likely due to increased screening in this subgroup.


IMPACT
Given the high prevalence of these exposures, these results may provide reassurance to the millions of women who are depressed and/or use ADs each year.