Glioblastomas are generally the only really common type of brain cancer precisely because your neurons aren't proliferating in adulthood, which is very much a good thing.

That's why I mentioned you should always be wary of anything that purports to increase neurogenesis, as even if it does, that can lead to significantly increased probabilities of cancer development. And brain cancer specifically, is one of if not the most difficult types of cancer to treat, with extremely limited survival outlooks.