For pretty much any A and B, you can create a perspective from which A is like B. The interesting question is "in which cases does this perspective give useful

For pretty much any A and B, you can create a perspective from which A is like B. The interesting question is "in which cases does this perspective give useful insights or solutions?" For treating a single animal, it's almost certainly useful to view it as a cancer. (Most drugs toxic to it will also be pretty toxic to the host, suppressing angiogenesis is helpful, etc.) From an epidemiology perspective, it probably behaves and spreads most like a bacterial infection. (Simple cell life cycle, limited environmental persistence, etc.) Parasites typically have a much more complex life cycle than these cells, and are much easier to target with drugs that won't harm the host. So... maybe there's a use case where thinking of it as a parasite is useful, but it's not immediately obvious to me.