Did the vet do a fine needle aspiration? They're not 100% accurate, but it can usually tell you if it is cancerous or not.
In your first post, you stated that the lump has grown. A lump that grows is not usually a good sign.
Last year, my chihuahua had a lump on her leg. The vet said it didn't look like anything to worry about and to bring her back if it grows. A year later it tripled in size. The vet suggested we remove it and get a biopsy. The lump turned and out to be cancer. Because of it's size and it's location, they were not able to remove it cleanly, so it has a high chance of growing back. Now, my poor dog is going through chemotherapy. If we would've removed it when it was small, she probably wouldn't have to get chemo now.