Changes In Cognitive Function In Postmenopausal Women 1 Year After Completing Adjuvant Letrozole Or Tamoxifen In The Breast International Group (Big) 1-98 Trial.

510 Background: Hormonal therapy for breast cancer (BC) may affect cognition. Methods: Post-menopausal women with hormone receptor positive, early-stage BC were randomized to receive either: A) tamoxifen for 5 years; B) letrozole for 5 years; C) tamoxifen for 2 years followed by letrozole for 3 years; or D) letrozole for 2 years followed by tamoxifen for 3 years, as adjuvant endocrine treatment. During the fifth year of trial treatment, objective cognitive function (speed of psychomotor function, visual attention, working and verbal memory, learning) was evaluated by computerized tests. The difference in the composite score for patients taking letrozole (B+C; N= 65) versus tamoxifen (A+D; N = 55) at the time of testing was the primary comparison. Scores for each domain were standardized according to age-specific norms. Two-way ANOVA controlling for language was used to test the effect of treatment on cognitive function. Self-reported subjective cognitive function, psychological distress, fatigue and quality of life were also assessed. Results: Patient characteristics were balanced between groups. Both groups performed below age norms on most domains. The group taking letrozole had better overall cognitive function than the tamoxifen group (difference in mean composite scores = 0.278, p = 0.038, 95% CI: 0.015–0.540) and outperformed patients on tamoxifen for all domains (n.s.). Comparison of monotherapy arms A versus B supported better cognitive function among letrozole patients. Subjective cognitive function, psychological distress, fatigue, and quality of life did not differ between groups. Conclusions: Although letrozole results in lower circulating estrogen levels than tamoxifen, in this study BC patients taking adjuvant letrozole during the fifth year of treatment had better cognitive functioning than those taking tamoxifen. [Table: see text]