The results from the newly published study by Ravishankar Jayadevappa et al  are in line with previous studies in which use of androgen deprivation therapy (ADT) by men with prostate cancer was associated with a subsequent diagnosis of Alzheimer’s disease.
However, almost all previous studies and the current one have analyzed the association between Alzheimer´s dementia and ADT in men with prostate cancer using those unexposed to ADT as reference. To make this comparison the studies needed to be adjusted for selections mechanisms (confounding), since younger and healthier men will receive curative treatment and older and sicker men will be treated with ADT. And if not all the confounders could be adjusted for; this could explain the finding that men on ADT have a higher risk of Alzheimer´s dementia.
By contrast, in a previous study where men on ADT were instead compared with age-matched men without prostate cancer, there was no increased risk of Alzheimer´s dementia .
All observational studies are prone to unmeasured confounding. A randomized trial can completely exclude confounding, but such a study will never take place to answer the question about ADT and risk of Alzheimer´s dementia. So, we must wait for the results from more observational studies before finding an answer to this question.
- Jayadevappa R, Chhatre S, Malkowicz SB, et al. Association between androgen deprivation therapy use and diagnosis of dementia in men with prostate cancer. JAMA Network Open 2019; 2: e196562
- Robinson D, Garmo H, Van Hemelrijck M, et al. Androgen deprivation therapy for prostate cancer and risk of dementia. BJU Int 2019; doi:10.1111/bju.14666