It's not an emergency, but you need to have your veterinarian examine it very soon. Then the veterinarian can tell you whether it needs to be surgically removed or what. I recommend if anything is removed, you have the veterinarian send it for a pathology report. It's best to know for sure what it was, in case another one pops up again.
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Kathy Diamond Davis, author, "Therapy Dogs: Training Your Dog to Reach Others," 2nd edition, and the free Canine Behavior Series articles at http://www.veterinarypartner.com/Content.plx?P=SRC&S=1&SourceID=47