As someone who has lost loved ones to Cancer (not Ebola yet but anything can happen) it’s a poor choice of words however like the equally incendiary uses of the word rape it is valid within the English language.
It is common to talk of concrete cancer being the fast deterioration of badly constructed concrete structures or to refer to a blot on the landscape as a canker (same root as cancer). The word itself stems from the side growing nature of tumors (moving like a crab) which is why the star sign of the crab is also called Cancer.
So it comes down to personal choice are pylons a cankerous rape of the countryside?
Perhaps.
Perhaps the shock value of using the word in such a mundane context reduces the currency of language.
Personally I’m not in a mad rush to be offended but I can see how on a bad day someone dealing with the disease and the fallout from it would be justifiably offended.
It’s your words.