Hormone-modulating therapy for breast cancer, neurodegenerative disease

Results of a new study point to a link between exposure to tamoxifen and aromatase inhibitors and reduced diagnoses of neurodegenerative diseases, particularly Alzheimer’s disease, in women with breast cancer. The findings were published in JAMA Network Open.

Methods
For the retrospective analysis, the researchers used the Humana claims data set from January 1, 2007 to March 31, 2017. The data set contains claims from private payer and Medicare insurance data sets from across the United States, but primarily in the southeast. 

The authors identified information from nearly 58,000 women with breast cancer aged 45 or older. All had been actively enrolled in Human claims records for 6 months before and at least 3 years after their diagnoses. 

To determine the association between hormone-modulating therapy and diagnosis of neurodegenerative disease, a survival analysis was conducted. A propensity score approach was used to minimize measured and umeasured selection bias.

Findings
Of the women included in the analysis, 31.3% received hormone-modulating therapies versus 68.7% who did not. In the propensity score-matched population, exposure to the therapies was associated with a decrease in the number of women who were diagnosed with neurodegenerative disease. (2,229 of 17,878 p12.5%] versus 2,559 pf 17,878 [14.3%]; relative risk [RR] 0.89; 95% CI, 0.87-0.93; P< .001). Similar results were seen for Alzheimer’s disease (AD) (877 or 17,878 [4.9%] versus 1,068 of 17,878 [6.0%]; RR 0.82; 95% CI, 0.70-0.90; P< .001) and dementia (1,826 of 17,878 [10.4%] versus 2,116 or 17,878 [11.8%]; RR 0.88; 95% CI 0.83-0.93; P< .001). 

Conversely, incidence of amyotrophic lateral sclerosis appeared to be increased in women who were exposed to hormone-modulating therapies. No significant associations were seen between the drugs and incidence of multiple sclerosis and Parkinson’s disease.

The number needed to treat was 62.51 for all neurodegenerative diseases, 93.61 for AD and 69.56 for dementia.   

Conclusions
The authors said that the finding in AD “points to a potential specific biological mechanism associated with estrogen loss in the brain in the pathophysiology of AD. Alternatively, the results from the propensity score-matched populations could be due to a stronger association of cerebrovascular and respiratory disease with non-AD dementia. 

Based on their results, the researchers believe that counseling of women on selection of treatment for breast cancer “should include a careful discussion of the risks and benefits of each treatment option that may be associated with a reduced risk of neurodegenerative disease.”