Cancer also works as intended: it kills the host.

Cancer has no such intention. Like any other organism, it competes for resources with those around it, and survives if it is effective enough at that to do so. Given that it often best characterized by the genetic mutations it has developed relative to the host (thus, it may differ from you genetically significantly more than an identical twin), I believe it is entirely fair to call it a separate organism. An 'extremely effective cancer' (as terrible as this sounds), would survive without regard to the state of the host, as Tasmanian Devil Facial Tumor Disease, which is contagious (transmissible by bite), emerged from a single original host, and has been around for quite a while.

Proof WordPerfect is Cancer!!

I'm an OEM, I want to put WordPerfect on my computer, WordPerfect sued me. WaaHaa.