A recent retrospective study was conducted using Surveillance, Epidemiology, and End Results (SEER)-Medicare linked data of women aged 66 years or older who were diagnosed with nonmetastatic breast cancer (BC) between 2008 and 2015. SEER is a Medicare linkage dataset of cancer registries data. Endocrine therapy (ET) users, e.g., those receiving an aromatase inhibitor (AI) only (anastrozole, exemestane, letrozole), selective estrogen receptor modulators (SERMs) only (tamoxifen, toremifene, raloxifene), or an AI and a SERM.
The purpose of this study was to determine the association between ET utilization and dementia, considering multiple potential sources of bias and confounding. The primary outcome was incident all-cause dementia. Secondary analyses examined incident dementia type (e.g., vascular dementia, Alzheimer’s disease, other or unclassified dementias).
The follow-up period started 12 months after the BC diagnosis to avoid immortal time bias or survivorship bias, which occurs when there is a period during which the outcome of interest cannot possibly occur in one of the study groups. To further avoid bias, the study controlled for competing risk biases, including age, race, region, marital status, T stage, N stage, Charlson Comorbidity Index, and the use of radiation therapy, chemotherapy, and/or surgery.
Data from 25,777 women were included in the analysis. The median follow-up period was 32 months. The average age of the 19,128 women in the ET group was 76 years compared with 74 years among the 6,649 women who did not receive ET (P <.001). Women in the ET group were also more likely to be Caucasian, married, have T1 disease, have at least one positive lymph node, and received radiation therapy but did not undergo chemotherapy; these were all significant to P <.001.
Of the 2,869 incident or new cases of dementia, 10.2% occurred in the ET group and 13.9% occurred in the non-ET group. Initial analysis, including unadjusted univariate models, had found a statistically significant difference between the groups for dementia risk (P <.001), but this was attenuated when confounders and competing risk of death were accounted for, leading to no difference between the ET and non-ET user groups (P = .018). Results were similar for all types of dementia, even when propensity score matching was conducted.
The authors cautioned that their findings may not be generalizable to younger women; the study was retrospective; there was limited power to account for risk related to SERMs; smoking was not accounted for; and the study was of relatively short duration.
Nonetheless, this study provides reassurance to pharmacists who counsel older women on ET that therapy will not adversely affect their patients’ cognitive function.
The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.
« Click here to return to Breast Cancer Update.