So far, it appears to be a degenerative process with manifold causes still to be elucidated. Perhaps in ~50 years, there will be a wider corpus of knowledge and treatments to attack more of them.

Of note: Cancer and Alzheimer’s disease inverse relationship: an age-associated diverging derailment of shared pathways Molecular Psychiatry vol. 26, pp. 280–295 (2021)

https://www.nature.com/articles/s41380-020-0760-2