Yes, some interesting distinctions are born of attributing symptoms to devil spirits. Someone is said to be "possessed of" such and such spirit. Another is "under the influence of" a devil spirit (this was some how not quite as bad, but still a problem). Later, I remember when Don Wierwille died of cancer, the Craiggers wading in on this topic. He brought up the "spirit of infirmity" is as a devil spirit cause of physical disease. There might not have even been sinfulness on the part of the afflicted. It was an attack of the adversary. (Also, smoking too, maybe.)
I think cancer as devil spirit is a logical conclusion if you have first accepted the illogical premise that all life is spirit. We were taught that spirit was either spirit of God, a spirit of the devil, or the spirit of man (aka soul life). It's pretty easy to see this has big gaps as WW pointed out. What about fungus, plants, microbes, etc? In as much as cancer has "life of it's own", which category does it belong in? God is supposed to be all good so not Him. Obviously not a man, so that just leaves devil spirits.
But then as you point out, if cancer is a devil spirit affliction, what does that even mean? Is it in your mind (that was how it was supposed to work right?) or is it in your body at some level? The more you try to explain it, the farther off the rails you have to go.
In short, no, cancer is not caused by devil spirits.