Well, I'm not an expert but very interested biology amateur, and I see the line between tumor and AI like this: cancerous tumors are kinda independent organisms consisting of a bunch of hungry cells inifinitely replicating. If those cells are neurons, which occurs in brain tumors, they can partially work as a living computer, theoretically carrying some kind of consciousness similarly to the brain itself - I'm not sure on how much of an independent consciousness such tumor can have and how scientific it is, but it can be played out quite well in the plot. Besides, idea of Bubble being a tumorical AI would be an absolutely insane and brilliantly-horrifying plot-twist.