Cognitive effects of Tamoxifen in pre-menopausal women with breast cancer compared to healthy controls

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The selective estrogen receptor modulator, Tamoxifen (TAM), is one of the most frequently prescribed drugs for the treatment of breast cancer; however, its effects on the cognition of users have not been adequately studied. Although TAM is an effective anti-estrogen that blocks tumour growth in the breast, it could also influence the activity of other target estrogen sites, including the brain. The exact nature of this interaction is unknown.


A cross-sectional design was used to compare cognitive task performance of two treatment groups: 1) women using TAM for the treatment of early breast cancer (n = 23); and 2) age-matched, healthy women not using TAM (n = 23). All participants were pre-menopausal, and recipients of chemotherapy were excluded from the study.


It was found that TAM users scored significantly worse than controls on tasks of immediate and delayed visual memory, verbal fluency, immediate verbal memory, visuo-spatial ability, and processing speed.


Although limited by the lack of baseline data and pre-morbid intelligence measures, the results of this exploratory study suggest that at least in pre-menopausal women, TAM may exert a widespread negative influence on cognitive abilities.

Implications for Cancer Survivors

Larger, randomized, prospective trials are required to confirm these results; however, TAM use in pre-menopausal breast cancer may be associated with cognitive difficulties. Knowledge and understanding of these complications will be important for professionals in communicating both the benefits and risks of TAM use in breast cancer survivors.

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