Sorry to hear your dog has a worrying lump. I am a vet nurse (on mat leave) and in a rural area so we mainly see large dogs. 90% of our surgeries are lumpectomy's. Very few actually come back from pathology with bad results. And if the vet cuts enough good tissue away from around the lump then that can be the only treatment needed. Also the majority of lumps we see are just fatty tissue that has hardened. I hope this is the case with your boy. I know this is not info that will help, I just thought it would give you some hopeful thoughts.