[tickle me emo]

Ok guys, yesterday we welcomed rocco to our home, you can see him in the my babies thread of the my yorkie section of the page. anyways, everything was fine and dandy and just this morning i was playing around with him, and just rubbing him and i noticed a small lump on his back. Its not something we noticed in any of the visits to the breeders house before actually getitng him. he seems healthy and has had all the shots needed so far,. my question is, is this lump something i should be worried about?, we're taking him to the vet first time tomorrow, cause thats as soon as we can,...but any advice? should we call the breeder,...or anything.

thanks