Try searching for "brain cancer" on Amazon US. Then click on the Books category. The results actually make sense. If you leave the filter on all, it will rank

Try searching for "brain cancer" on Amazon US. Then click on the Books category. The results actually make sense. If you leave the filter on all, it will rank by the most popular items, and I can't imagine "brain cancer" being a common search term. Because the medical term for it is "brain tumor" and if you search the medical term you'll actually end up with book results that make sense. This seems to be much ado about nothing.