Effects of hormonal therapy on cognitive functioning in breast cancer patients: a review of the literature.

(Pre)clinical research suggests that estrogens play a role in brain- and cognitive functioning. It is, among others, hypothesized that estrogens have a beneficial effect on neurotransmitters that are involved in cognitive processes, protect the brain by exerting anti-inflammatory actions after ischemic injury, promote survival of brain cells, and increase cerebral blood flow and glucose transport into the brain. Neuropsychological studies suggest that natural changes in estrogen levels are associated with (small) changes in cognitive functioning, for example during the menstrual cycle. In estrogen substitution studies, however, contradicting results are found, suggesting that substitution can have both beneficial and detrimental effects on cognitive functioning. Hormonal therapy for breast carcinoma lowers estrogen levels or blocks the growth-promoting effects of estrogens. The neuropsychological studies conducted so far give, though they vary highly in design, measures and participants, some indications for effects on cognition: ovariectomy, treatment with LHRH analogues, anastrozole and tamoxifen seem to be associated with (small) negative effects on some tests. It is unclear whether those effects are reversible, and whether time on therapy is associated with the seriousness of the effects. Raloxifene, currently under study for breast cancer prevention, does not seem to have detrimental effects on cognitive functioning. For the aromatase inhibitors letrozole and exemestane no data are available yet. Because the role of hormonal therapy in breast cancer treatment is increasing, the medical grounds for prescribing are expanding and physicians can make a choice from a broad spectrum of hormonal treatments, potential effects on cognitive functioning should be part of long-term drug safety evaluations.