Non-mother kitten nursing and feline mammary cancer

Question
We recently adopted a kitten (Sylvester) and it has been nursing on our other cat (Katherine - 4 years old and not its mother).  Sylvester always seems to nurse in the same place, and now this teet is swollen on Katherine.  The nursing seems to have stopped (mostly), but the teet is still swollen (not red anymore) and soft.  Is this normal and will the swelling subside, or should I take Katherine to the vet?  I don't want to ignore possible cancer but don't want to overreact.  Thanks!

Answer
I would suspect an infection first before cancer.  If there is still milk in the teat, you can just try warm compresses on the area and keep the kitten away from her.  If you are unable to get milk out of the teat and it is still swollen, then I would take her to the vet.