Null association between tamoxifen use and dementia in Danish breast cancer patients.

BACKGROUND Concerns have been raised about the risk of dementia associated with antiestrogen adjuvant therapy in breast cancer, but study results have been inconsistent. We examined whether tamoxifen or other endocrine therapy was associated with dementia risk in a large population of patients with breast cancer. METHODS We used Danish nationwide medical registries to identify patients with breast cancer diagnosed between 1990 and 2004, use of endocrine therapy, and subsequent diagnoses of dementia. We used Cox regression to estimate the risk of dementia among patients who received five years of tamoxifen or other endocrine therapies. RESULTS The study included 16,419 patients with breast cancer. In this cohort, 37% were unexposed to endocrine therapy, 9% had five years of tamoxifen therapy, and 54% had other endocrine regimens, some of them containing tamoxifen for less than five years with subsequent aromatase inhibitor therapy. Tamoxifen therapy was associated with a near-null risk of dementia [HR, 1.4; 95% confidence interval (CI), 1.0-1.9], and a null association was observed after death was taken into account as a competing risk (sub-HR, 1.0; 95% CI, 0.76-1.4). CONCLUSIONS No clinically relevant association between use of tamoxifen or other endocrine therapy and risk of dementia was observed. IMPACT Our result contradicts earlier research findings suggesting tamoxifen and other endocrine therapies increase the risk of dementia in breast cancer patients.