Association of breast cancer therapy with cognitive decline in older women with early breast cancer: Findings from the CLIMB study

Studies investigating the long-term effects of breast cancer treatment on cognition in older breast cancer survivors are lacking, even though intact cognition is a highly valued outcome by the older population. Specifically, concern has been raised about detrimental effects of endocrine therapy (ET) on cognition. Therefore, we aimed to investigate longitudinal cognitive functioning and predictors of cognitive decline in older women treated for breast cancer. We prospectively enrolled Dutch women aged 70 years or older with stage I-III breast cancer in the CLIMB study. The Mini-Mental State Examination (MMSE) was performed at baseline, and 9, 15 and 27 months. Longitudinal trajectories of MMSE scores were analyzed for the minimal clinically important difference (2.3 points) in the whole cohort and in women treated with ET. To compare MMSE scores between patients with impaired and normal cognition and to identify the association between possible predictors and cognitive decline, linear mixed models were estimated. Among the 273 participants, mean age was 75.8 years (standard deviation (SD) 5.2) and 48% received adjuvant ET. Mean MMSE at baseline was 28.24 (SD 1.95). Cognition did not decline over time to clinically important differences in the whole cohort or in women receiving ET. MMSE scores of women with pretreatment cognitive impairments improved over time (significant interaction terms) in the whole cohort and in women receiving ET. Older age, lower education level and impaired mobility were independently associated with cognitive decline, but this decline was not clinically significant. Cognition of older women with early breast cancer did not decline up until two years after treatment initiation, irrespective of endocrine therapy. Our findings might indicate that fear of declining cognition does not justify de-escalation of breast cancer treatment in older patients.