Effects of tamoxifen and exemestane on cognitive function in postmenopausal patients with breast cancer

Background: Cognitive effects of tamoxifen have been described. We augment data from a previous short-term (ST) follow-up study with long-term (LT) data to evaluate ST and LT cognitive effects of tamoxifen followed by exemestane and exemestane in breast cancer patients. 

Methods: Patients from the Tamoxifen and Exemestane Adjuvant Multinational trial received 5 years exemestane (exemestane group, n = 114) or 2.5 years tamoxifen followed by 2.5 years exemestane (sequential group, n = 92). Neuropsychological performance was assessed pre-endocrine therapy, after 1 year (ST follow-up) and at 5 years (LT follow-up). A control group of healthy participants (n = 120) were assessed with parallel intervals. With random effects modeling we evaluated cognitive changes from baseline to ST and LT follow-up. Statistical tests were 2-sided. 

Results: After controlling for age, intelligence quotient, attrition, menopausal symptoms, anxiety and/or depression, and/or fatigue, the sequential group showed ST and LT decline compared with control participants on verbal memory (effect size [ES] = 0.26, P = .01; ES = 0.34, P = .003) and executive function (ES = 0.27, P = .007; ES = 0.38, P = .002). Compared with the exemestane group, the sequential group demonstrated ST decline on information processing speed (ES = 0.33, P = .01) and executive function (ES = 0.32, P = .01) and LT decline on verbal memory (ES = 0.33, P = .02). The exemestane group showed no cognitive decline compared with control participants. 

Conclusion: Cognitive adverse effects of tamoxifen alone and after switching to exemestane were observed, suggestive of a carryover effect of tamoxifen. Our results underline the need for well-controlled, prospective trials studying cognitive effects of endocrine therapy.