In contrast to the antiestrogen effects of tamoxifen in breast tissue, tamoxifen exerts estrogenic agonist action, showing neuroprotective function against amyloid-β.39 Aromatase inhibitors reduce the peripheral levels of estrogen but increase estrogen levels in specific brain regions.40 In addition, upstream precursors of estrogen, such as testosterone and androstenedione, are increased by aromatase inhibitors and may benefit cognitive function.41 Previous epidemiologic studies also support the use of tamoxifen and aromatase inhibitors to be associated with a lower risk of AD.7,42. This evidence concerns the gene CYP19A1 and Alzheimer disease.